How many of y'all are using iron pistons?

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Model T Ford Forum: Forum 2013: How many of y'all are using iron pistons?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Monday, April 15, 2013 - 12:48 pm:

Just another random thread here. I'm just curious to know how many are still using the ol' iron pistons?

I say this because last weekend, I finally installed new piston rings on the iron pistons in my '24 Touring, so they are on my mind.

It had been needing them for a while. It was constantly burning oil and making nice clouds of blue smoke, plus fouling spark plugs, making the cylinders a mess, etc,. With the new rings installed, I started her up and guess what? No smoke! How nice is that?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ed Baudoux on Monday, April 15, 2013 - 12:55 pm:

Currently overhauling Dad's '27 Fordor. Nice straight bores, stock iron pistons. It is going back together with N.O.S. piston rings on the stock pistons.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Just a little South West . on Monday, April 15, 2013 - 12:59 pm:

everyone that l know who use cast iron pistons swear by them for added momentum ( reciprocal mass or something like that )better torque than alumin.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dexter Doucet on Monday, April 15, 2013 - 01:09 pm:

Yep on a 15 roadster with a worn motor. Burns oil too but doesn't always smoke. This car currently see's very little use.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Monday, April 15, 2013 - 01:13 pm:

Both of my cars still have the iron pistons. One of them needs to have new rings installed. I set the clearance on the rods last year but I should have done the rings then too. I don't have a problem with the iron pistons but if a person is going to do a major on their engine they would be dollars ahead going to a slight bore to straighten any taper in the cylinder and correct roundness too. Then put in the aluminum pistons and new rings.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john kuehn on Monday, April 15, 2013 - 01:34 pm:

I had 2 sets of .003-.005 oversize rings for use with standard pistons in worn standard bore engines.
They were in a storage bldg that had a bad roof and they were ruined.
Now I wish I had them for the engine I am planning to build up from good parts for a fun around the farm car.
I have a good block thats standard but has minor wear.
I have a nice set of cast iron standard pistons and they will be used for sure. I guess I will buy a set of standard rings to use on them.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan B on Monday, April 15, 2013 - 01:53 pm:

Is there anything else?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Monday, April 15, 2013 - 01:53 pm:

i purchased a 20 speedster with domed iron pistons. Im not taking it apart till she throws a rod! haha


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike on Monday, April 15, 2013 - 01:55 pm:

For the average T owner wouldn't aluminum pistons be better in the long run regarding less strain on the crank (as these cranks get older, isn't a question of "when" rather than "if" they will fail?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jared Buckert on Monday, April 15, 2013 - 05:06 pm:

I think aluminum pistons would be better for an old crank, but if you've bought a new reproduction crank maybe it would be better to have the extra rotating mass of the iron pistons. I bet this would be a good question for the Tulsa T club guys. They seem to have all the performance information.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Monday, April 15, 2013 - 09:50 pm:

I can not see that Iron pistons are extra rotating mass, they do not rotate, the reciprocate, meaning they have to change directions four times for every power stroke. It would seem to me that less mass would be easier to change directions.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Aaron Griffey, Hayward Ca. on Monday, April 15, 2013 - 10:48 pm:

If heavy pistons or iron pistons were better they would be still using them in today's cars.
with the T engine limited to around 1600 RPM it was not too important.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Monday, April 15, 2013 - 10:59 pm:

Semantics.......I think Jared meant inertia.....but never mind.
My '20 coupe (not any more...... ;) ) has cast iron pistons.
It's among the smoothest running engines I have ever seen.
My '19 touring has aluminum pistons and there is a pronounced difference.......not necessarily for the better.
Upon the new owner driving "my" coupe last week the first thing he said >>> "Holy crap that thing runs smooth"...... :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Monday, April 15, 2013 - 11:19 pm:

Semantics or not, inertia is going to work against you with heavy reciprocating parts, as the pistons change direction twice each for every rotation of the crank.
Best
Gus


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jared Buckert on Monday, April 15, 2013 - 11:58 pm:

Craig, thank you. That's what I was trying to say. I guess I need to brush up on my physics terminology.

But as you force one piston down by the combustion of the air/fuel mixture wouldn't the inertia of that piston be transferred via rotation of the crankshaft to another piston moving upward in its respective cylinder? Or am I just over-thinking the transfer of kinetic energy in the system? I'm not a physics major, so I could easily be wrong.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Just a little South West . on Tuesday, April 16, 2013 - 12:19 am:

I think its all about the difference in getting up that hill, from what l have been told and seen, a cast iron piston engine seems ( l'll use that word sparingly - l have HC Domed alumin )to have more pulling power " due" to the additional weight rotating with in it...
I am not a physics major either.... but l see what l see... when l werae my glasffres.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Tuesday, April 16, 2013 - 12:23 am:

David - Sort of like a heavier, or bigger diameter flywheel, huh?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Tuesday, April 16, 2013 - 12:25 am:

Yeah, me and Jared might both be a bit lacking on our knowledge of "fizzicks", right Jared?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Tuesday, April 16, 2013 - 06:29 am:

2 of 3 "T"s with CI pistons. Sweet running and very happy at 29-32 MPH.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Andre Valkenaers on Tuesday, April 16, 2013 - 07:06 am:

Hello,

I even reused the old rusty once that came out of the rusty engine and put new rings on it. Just replaced one that was cracked.
Engine is running well and with a lot of power.

Andre
Belgium





Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Tuesday, April 16, 2013 - 07:16 am:

Heavier reciprocating parts equal less power. It's a fact.

A piston accelerates to speed each time it changes direction. The amount of force required to accelerate a lighter object to any given speed is less than that required to accelerate any heavier object.

If you believe your engine with cast iron pistons is more powerful you are mistaken.


Top of pagePrevious messageNext messageBottom of page Link to this message  By don ellis on Tuesday, April 16, 2013 - 07:51 am:

This is what I found in my 11. The fit was good so I left them. 31 OS


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Tuesday, April 16, 2013 - 07:52 am:

Royce, first part, that is so wrong,
second is right when chasing rev's and
third is a problem in your believes.
Low revving, high torque diesels use cast iron pistons, marine, truck, tractor, stationary, you name it, Cat, Cummins, Detroit, Perkins, Volvo, all the Jap lines and the list go's on.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Tuesday, April 16, 2013 - 08:04 am:

Kerry,

You are quite the man if you can prove that Sir Isaac Newton - and I - are wrong.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Tuesday, April 16, 2013 - 08:27 am:

Royce, I don't have to, the auto industry can, just a quote from Mazda alone is, Using forged steel instead of cast iron pistons, which means fuel economy and "torque" will diminish by about 3 to 5%


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Rutherford on Tuesday, April 16, 2013 - 09:06 am:

Not to stir things up, but it depends on what is meant by "power". For best peak HP, lightweight parts would be best since revs are important. (A formula 1 car would be the best example of this). For best torque, heavy parts are good but you won't get the revs. (Diesel motors, farm machinery, etc).

I'm just talking "in general", not Model T specific.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, April 16, 2013 - 09:44 am:

I think like all things, this might not be as simple as it seems. I think in a way both Royce and Kerry are correct. I will try to explain.

Imagine the piston travelling in a no power situation - which it does every time it travels from BDC to TDC and from TDC to BDC on the intake stroke. The crank imparts energy to the piston through the rod. As the piston overcomes inertia it draws power from the system. This requires a great deal of power at first for two reasons. One, the piston is at a dead stop and two, the rod angularity is such that the leverage is at the maximum disadvantage. At some point in time the piston will have more momentum than the power needed to move it so it will begin to impart power back into the system. According to the second law of thermodynamics you will always have a net loss of power with this system.

But, on the power stroke, things are different. A heavier piston can actually make the system more efficient.

The power imparted into the piston is the result of combustion pressure. Combustion pressure is at its maximum shortly after TDC and rapidly dissipates in a more or less logarithmic fashion. Therefore the pressure is greatest when the rod angularity is near its point of maximum disadvantage. You have a bunch of power when it does you the least good. As with the idle strokes, there will be a point when the momentum of the piston will be greater than the power needed to move it either by the crank or the combustion pressure. It is possible that this could be when the rod angularity is at or near the point of maximum advantage (around 90 degrees after TDC).

Here is another way to look at it. The combustion pressure essentially "shoves" the piston. It does not push it along steadily with equal power from top to bottom. If you shove something with more mass it will have more inertia to do work later, and in the case of a piston later is better because of the mechanical advantage you have from the better leverage of the rod angle.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Tuesday, April 16, 2013 - 10:01 am:

Tom, the flaw with the shove imparting power to a heavy piston does not take into account that the shove happens when the piston is moving slower because of the arc of the crankshaft, it has to accelerate until it reaches the halfway point in the stroke. where it will start to slow. A heavier reciprocating part will accelerate slower and decelerate slower due to inertia, resulting is an engine that will not run as smooth as one with lighter reciprocating parts.
Another problem with heavy parts in the T engine is that all pistons change direction at the same time, with 6 or 8 cylinder engines, the crank shaft has pistons at every point in the stroke, and as a piston changes direction, several others help it with their inertia of movement.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mack Cole ---- Earth on Tuesday, April 16, 2013 - 10:12 am:

Cast iron worked for 15 million cars.Does that not say something?
If I have the option while repairing a engine,it will have cast pistons.Ford designed and built the model T with cast pistons.Are we that much smarter than Ford?
And by the way,it would be a challenge to find a T that runs better than Don Ellis's 1911.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Tuesday, April 16, 2013 - 10:17 am:

Mack,
I do not challenge cast iron pistons as a working design, but I will argue that they are not a benefit to the engine because of inertia but the opposite. I was not aware that Ford did not use aluminum pistons until newer designs though, when did Ford start using aluminum pistons, and if they were no benefit, why would he use a more expensive metal?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, April 16, 2013 - 10:18 am:

A. G. B., I didn't say it would be smoother, I was trying to show how it might produce more torque. The piston is "banking" energy from the shove. A heavier piston is a bigger "bank" than a lighter piston.

No doubt all things being equal a four cylinder motor with lighter pistons will run smoother than one with heavier pistons.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Tuesday, April 16, 2013 - 10:34 am:

OK Tom, I can see your point, bit I think for that to be true, the bulk of the power of the combustion must be produced just before the midrange of the stroke, and to me a 1/4 turn out of two revolutions seems a small bank.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Tuesday, April 16, 2013 - 03:08 pm:

I really enjoy reading y'all's posts, but the main purpose of this thread was just to see who is still running iron pistons, not their advantages or disadvantages!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jared Buckert on Tuesday, April 16, 2013 - 05:13 pm:

Cameron, From what I see here there are a lot of people still running the iron pistons. Sorry for the thread drift. But I think there's some good talking points here. I think the only way to put this debate to bed for good is to build two identical cars, except one has aluminum pistons and the other has iron, and put them on a dyno. Otherwise we are simply arguing theoretically. It is an interesting debate, though. I feel like there's learning going on here.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Tuesday, April 16, 2013 - 05:32 pm:

If I had a good running Model T engine with iron pistons I would use them, and re-ring them if needed. If I pulled that same engine out to grind the crank and re-babbitt I would use aluminum pistons.

One thing about the iron pistons, the bottom ring drops below the bottom of the cylinder. The oil ring must be one piece. Sears in the 1960's sold a set of rings with a 3 piece oil ring which can pop out and crack a piston. You can guess how I found this out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Killecut on Tuesday, April 16, 2013 - 05:59 pm:

I still have cast irons in a couple of my cars. One is my 20 Touring, with many many miles on it. This is the smoothest running "T" I own. It's fast on the flat, but dead on hills. It has the standard Model T gearing. My original 13 still has the cast iron pistons. These earlier cast irons are heavier than the later cast irons. The 13 goes down the road as you would normally expect. On hills, its a bear. It out performs the 20 and the 20 has a Rusckstell in it. On hills, it also out performs my other T's that have aluminum pistons. So, opinions are opinions, and all I am pointing out is the performance of these two cars.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Borland. Bathurst. NSW. Australia. on Tuesday, April 16, 2013 - 06:59 pm:

Iron in the '23, Iron in the '26 waiting to be awakened up in the not too distant future. If the '26 runs OK it will get new rings and live again.

Peter


Top of pagePrevious messageNext messageBottom of page Link to this message  By mike_black on Tuesday, April 16, 2013 - 08:35 pm:

Ted,
When I tore apart my TT in 1977, about an inch of one of those 3-piece rings had popped out and been running for years squeezed between the piston and cyl wall. Cylinder wall looked like a half gallon of ice cream after the first scoop is removed. I found another 25 block that was in great shape and was still standard size. I had a NOS set of std cast iron piston, so, I used them when I put it back together. Still runs great. I have alum pistons in my speedsters--(along with downdraft carbs, distributors and no magnets on the flywheels.)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Schrope - Upland, IN on Tuesday, April 16, 2013 - 11:10 pm:

What's the difference in weight between the cast iron and aluminum? I've never weighed them, but have heard that there isn't as much difference as you'd think. I'll bet Tom knows.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Tuesday, April 16, 2013 - 11:29 pm:

When did this turn into a debate about POWER?
Can't ANYTHING around here stay on track?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Matthew David Maiers on Tuesday, April 16, 2013 - 11:46 pm:

no.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Tuesday, April 16, 2013 - 11:55 pm:

There is no increase in power using cast iron pistons. There is no testing required, the test has already been competed. If folks got more power out of an engine with cast iron pistons, then all Montana 500 racers would run cast iron pistons. Some have ran cast iron but there is no real power advantage.

The difference in weight is:
CAST IRON
bare 810 gram
rings 125
pin 117
-----------
Total... 1052 gram

ALUMINUM
bare 586
rings 69
pin114
----------
Total... 770 gram

The real advantage of aluminum pistons is the lighter weight and the reduced load on the rods and crank bearings. Give two engine, one with CI and one with AL and increase the the speed till they self destruct, the CI piston engine will blow first. Model T engines seem to be pretty resistant to rod failure due to over speed but that was not the case with many early cast iron piston engines. Aluminum pistons really reduces the chance of shaking hands with a rod sticking out the side of a block.

Here is a link to the last time this was discussed:
http://www.mtfca.com/discus/messages/50893/79442.html?1232560406

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep NZ on Wednesday, April 17, 2013 - 03:19 am:

Cast iron pistons have picked up momentum after most of the combustion is over. This they can impart to the crank and other pistons when there is no longer force being applied from the combustion cycle. This also helps the piston in the cylinder next to them compress the gasses as the added momentum would overcome the force of the gas being compressed. However, The cast iron pistons in theory are taking the extra energy they helped save during compression cycle to make them reciprocate. The moment this occurs would be shorter in time frame than the moment from combustion-to-combustion of an alloy piston engine. If you look at the geometry of piston height relative to the crankshaft centre the total piston centre of gravity in a 4 cylinder would move ever so slightly so one would expect to see the lighter alloy pistons as smoother. i lack the knowledge of every weight of all pieces of a model T but it appears the shift of total piston weight relative to crankshaft centre is not that much for the total of reciprocating weight.
In short, For the slow model T this would give the cast iron the illusion of being smoother but at the expense of RPM.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Wednesday, April 17, 2013 - 06:26 am:

Would any increase in "banked" energy in the heavier CI piston on the power stroke be negated by the extra force required to move the other 3 heavier CI pistons compared to 4 AL pistons?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Schrope - Upland, IN on Wednesday, April 17, 2013 - 09:11 am:

Does anyone have a graph of the pressure inside the combustion chamber during the 180 degrees of the power stroke? That would interest me.

Debate??? I don't see any. I do see intelligent discussion and learning.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Wednesday, April 17, 2013 - 09:28 am:

If heavy reciprocating parts are an advantage, then why have reciprocating parts been reduced in weight at the expense of more costly materials? If heavy reciprocating parts did improve performance, they would have made the crankshaft heavier. If I recall correctly, the heavy rods are not readily available from rebuilders, and they will not take them as a core.
Reciprocating parts rob power from the engine, rotating parts rob the engine of quick acceleration, but there is a certain amount of weight required to overcome the weight of reciprocating parts, and that is why the flywheels must be as heavy as they are.
A good example of this is in a hay baler, the plunger is built rather light, as it is a reciprocating part, but it need mass and inertia to cut and compress the hay, so that is done with a very heavy flywheel.

One component that Jim T left out of the weights is the rod, how much lighter is the newer rod? Also, it must be borne in mind that the rod is not all reciprocating weight, the crank end is rotating weight


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Wednesday, April 17, 2013 - 11:09 am:

Just to give a little credit, reciprocating parts make an engine go, whether the pistons are aluminum or iron.

Neither iron nor aluminum have been blessed by the almighty and each have their good and bad points. Likely, still yet, there as many Model T's running iron pistons as there are those with aluminum pistons.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Wednesday, April 17, 2013 - 11:43 am:

Hey Ted,
Your comment caused me to think, there is a designs where there are no reciprocating pistons, that is in the rotary engines, the modern rotary has no pistons, and the classic rotary has pistons that do not move up and down (reciprocate). the pistons in the classic rotary are actually rotating mass and as such work as flywheel weight


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Wednesday, April 17, 2013 - 12:14 pm:

First off, sorry for the thread drift, but that is the nature of discussion. In the words of the philosopher - "drift happens".

Erich asked: "Would any increase in "banked" energy in the heavier CI piston on the power stroke be negated by the extra force required to move the other 3 heavier CI pistons compared to 4 AL pistons?"

I would say "no". The the momentum force is largely (but not completely) returned. Sort of like compressing a spring - when you release it you get most of the compression energy back whether it be a big spring or a small one.

Fred asked: "Does anyone have a graph of the pressure inside the combustion chamber during the 180 degrees of the power stroke? That would interest me."

The graph would not be the same at all speeds as there are several components of pressure dissipation. e.g.

1. Cylinder volume - as the piston moves down the volume of the cylinder increases, which lowers the pressure.

2. Heat dissipation - as the gasses cool, they lose pressure.

3. Leakage.

The first is a function of crankshaft position, the others more or less a function of time. In other words, there will be less heat dissipation relative to any given crank position at higher speeds.

A.G.B. asked: "If heavy reciprocating parts are an advantage, then why have reciprocating parts been reduced in weight at the expense of more costly materials?"

Three reasons that I can think of:
1.Vibration, as discussed earlier.

2.Stress on bearings etc. from added load.

3.There is obviously an ideal balance between the function of imparting combustion force to the crank and kinetic energy storage.

I will try to explain the third point with an analogy.

Pretend that you are at a bowling alley. You have three bowling balls. One is made of normal bowling ball material, one is a hollow plastic ball about the size of a normal bowling ball, but just weighs a few ounces. The third is about the size of a normal bowling ball but is made of osmium and weighs over a hundred pounds. Assume that all three balls have the same rolling friction. Across the foul line you have tied a big rubber band that is perhaps made out of an inner tube. If you stretch the rubber band to given point, say three feet and release it, it will impart a certain like amount of energy every time.

If you were to pull back the rubber band and shoot the hollow plastic ball down the alley, it would initially have a great deal of velocity, but would have little effect as far as knocking down pins.

If you were to pull back the rubber band and shoot the normal bowling ball down the alley, it would initially have a less velocity, but would have good effect as far as knocking down pins.

If you were to pull back the rubber band and shoot the osmium ball down the alley, it would initially have very little velocity, and may not even have enough stored power to make it down the alley.

In this analogy:

The rubber band = combustion pressure

The velocity of the ball = energy imparted to the crankshaft by the piston.

Pin action = the energy stored by the piston to do work later.

As you can see, there is a compromise between the two needs and obviously an ideal mass for the piston to have - which will change depending on the speed of the motor and possibly other factors.

By the way, I have had a few top five finishes in the Montana 500 with cast-iron pistons in the past.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Wednesday, April 17, 2013 - 12:44 pm:

Hey Tom
I like your analogy, but I still have a problem with any mass imparting energy to another mass when both come to a dead stop at the same time. It is the inertia of the stopped pistons that I believe will rob the engine of power, and in the T all of the pistons are stopped at the same time. the maximum stored energy in the power piston comes at a time when all of the pistons are slowing down. My argument would not be as strong in any engine with more than 4 cylinders,


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Wednesday, April 17, 2013 - 01:05 pm:

Vibration in the engine should not be effected by the weight of the pistons. In the whole engine, two pistons are going in one direction and the other two are going in exactly the opposite direction canceling out any effect out side the engine. The load on the rods and bearings is greater with heavier pistons.

When looking at just one piston or the whole engine, it come down to the law of conservation of energy. You can not create energy of destroy it. With a heavier piston it takes more energy to get the piston moving from a dead stop but the exact power it takes to get it moving is returned to get it stopped again. Again, the load on the rods and bearings is greater with heavier pistons but energy is conserved in either case.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Wednesday, April 17, 2013 - 01:13 pm:

A.G.B. said: "the maximum stored energy in the power piston comes at a time when all of the pistons are slowing down."

I don't understand what you are saying here. Could you please rephrase?

Jim said: "In the whole engine, two pistons are going in one direction and the other two are going in exactly the opposite direction canceling out any effect out side the engine."

Not true. The pistons travel at a different speed in the top half of the bore than in the bottom half due to rod angularity. The force therefore is not offset.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth from NC on Wednesday, April 17, 2013 - 01:47 pm:

"The pistons travel at a different speed in the top half of the bore than in the bottom half due to rod angularity. The force therefore is not offset."

Not saying you're wrong, but I'm not wrapping my brain around that statement. I get that the piston travels at different speeds - faster in the middle than towards either end. But if the end of the rod that is connected to the crankshaft travels in essentially a perfect circle, I don't see how the piston travels faster on one half of the stroke.

On a clock face if 12 is TDC and 6 is BDC, facing the engine 9 is the passenger side and 3 is the driver's side. Going clockwise, from 7:30 to 10:30 you get the most verticle speed and verticle travel, from 10:30 to 1:30 you have a lot of lateral travel but very little change in height, then basically the exact same thing happens from 1:30 to 4:30 and 4:30 to 7:30 respectively. How is it then that the pistons don't offset one another when they are on opposite ends of the clock? The only way you'd get that effect is if the travel of the rod end was eccentric with the pointy part of the egg towards TDC.

If this were the case, if the travel of the rod end was eccentric, no amount of balancing would be able to fix the vibration that would cause. You can balance the engine because having the pistons all weigh almost exactly the same gives you the most perfect offset (along with balancing the rotating portions). At least that is how it all works in my brain, if that's wrong I'm open to having it set straight. Anybody see what I'm saying?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Wednesday, April 17, 2013 - 02:22 pm:

Seth, the pistons do indeed travel faster on the first 90 degrees of rotation. Maybe I can explain it a little better so you can get your head around it.

Imagine a motor with a 4" stroke. The mid point of the piston would be 2" down. Imagine the piston at the top of the bore. With the rod hanging down, the rod hole would be 2" above the center line (main bearing line) of the crankshaft. Now, turn the crank 90 degrees. Push the piston down 2". At this point the rod hole will be in line with the crank center line if the rod was allowed to hang straight down. You can see that in order to connect the rod to the crank pin you would have to pull the piston down a bit to accommodate the rod angle.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth from NC on Wednesday, April 17, 2013 - 02:54 pm:

Bingo, light bulb goes on. I'm tracking now. So for the top half by the time the crank travels 90* the piston has actually traveled further than 2 inches. It's really more like almost 2.5 inches. Conversely, on the opposite end of the crank the pistons coming from BDC have only traveled 1.5 inches when the crank hits 90*. So where all 4 pistons are level, with the crank at 90*, they all line up about 2.5 inches deep in that 4" stroke.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Stewart -Calif. on Wednesday, April 17, 2013 - 02:59 pm:

Still using the iron pistons that came on my T Runabout. The T was assembled on 12/13/1913 so I think they will make it to 100 years old. She runs good and terrorizes the neighborhood weekly. A little smokey though.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Wednesday, April 17, 2013 - 03:09 pm:

Tom,
Your explanation is one of the most irritating things I have read in this post, I have thought of 10 ways to prove you wrong, but unfortunately none of them work because you are right.
My comment about maximum storage of kinetic power of the piston come when the piston is slowing down is because I believe (perhaps wrongly) that the greatest thrust from combustion happens in the first half of the downward stroke, and as the crank end of the rod passes the 90 degree mark, it has to slow down.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Rutherford on Wednesday, April 17, 2013 - 06:41 pm:

I'm surprised no-one has mentioned the reason I always heard for the use of aluminum pistons. - heat dissipation. The way I understood things, AL pistons don't get the hot spots that iron pistons do, especially when compression and RPMs go up. I always heard this was fully realized when Bentley race cars in the '20's could run an entire endurance race at an even pace burning little oil with high compression. Anyone seen the old films of car races from the teens? Notice how smokey those cars are? Better understanding of metallurgy changed that.

If anyone else is into motorcycles, Kevin Cameron has written a lot about engine development and how cars, 'cycles, wartime and airplanes all forwarded technology.

Again, on a T driven on the street, I don't know how much of this matters. Use what ya got.

My 2 cents...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ed Baudoux on Wednesday, April 17, 2013 - 07:25 pm:

On the subject of heat. GM's variable displacement system shuts down cylinders based on engine load. Many customers are experiencing oil consumption at relatively low mileage. It seems the off-duty cylinders cool off, shrinking the pistons. The 5w30 oil does not help things.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Wednesday, April 17, 2013 - 08:13 pm:

Ed, the absence of compression on the missing power strokes means there is nothing there to push oil back down the pistons too.
I know this from belting up old tractors at the shop to limber them up, check for governor action, any strange noises or whatever else before actually starting.
Invariably they suck oil past the pistons and things can get messy.
Once running the problem goes away.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Schrope - Upland, IN on Wednesday, April 17, 2013 - 08:53 pm:

Ed & Craig
Both interesting. Didn't Cadillac try the dead cylinder thing about 25 years ago or so. IIRC, it didn't work then either. Oh what the car manufacturers have to go through to meet the government requirements.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Wednesday, April 17, 2013 - 09:19 pm:

Tom,
You are correct, the pistons travel at a different speed in the top half of the bore than in the bottom half due to rod angularity. The total force to go from the top to bottom occurs more at the top then the bottom but the average for each 1/2 rotate is equal.

I wonder how much difference that would make. For a horizontally opposed engine the force would be exactly the same. Do horizontally opposed engines have noticeably less vibration? It must not be too big of an issue, otherwise all engines would have migrated to a horizontal opposed configuration.

Jim R,
Interesting point on hot spots in the piston. I think just based on the ability of the piston to handle temperature and lubrication extremes that the cast iron would have an advantage. We have all seen scuffed and even seized aluminum pistons when the going get tough. Cast iron is kind of self lubricating because of the free carbon content.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Wednesday, April 17, 2013 - 09:26 pm:

Hey Jim,
The 4 cylinder opposed engine in my Taylorcraft runs very smooth, much smoother than any inline 4 cylinder engines I have been around, it may be the opposed cylinders, but it is almost like comparing apples to oranges. The dual ignition is probably a factor too.
Best
Gus


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Hycner on Wednesday, April 17, 2013 - 09:38 pm:

Here we go again...
One thing I take away from this forum is the valuable advice from the collective membership. without it I could not have gotten my T running. But sometimes it is tough to decide on what advice to take and do not want to dismiss anyone's thoughts. So I compiled a list of the most common discussions and went with the following.
Pistons:
2 cast iron
2 aluminum, 1 regular the other hi-compression
Bands
1 Kevlar
1 Cotton
1 wood
Oil
1 quart 10/30
1 quart 5/30 synthetic
1 quart straight 30
and a mix of kerosene, marvel mystery oil and a little ATF
Cooling
Water pump and a thermostat under the seat, just in case
Sorry but I just could not resist :-)
And my car runs great.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, April 17, 2013 - 09:39 pm:

I think at the end of the day, cast iron pistons were used for a simple reason,
they lasted longer,
listed as one of the reasons why still used today in lugger type engines.
I have ads for rebuilding engines dating back to the early teens of fitting aluminium alloy pistons, but the down fall was something that Constantine had said the other night about his T when he hit the African roads which of course his photo's showed that they would be no better than the early days of motoring world wide.
He had an air cleaner fitted, 4 spare elements, some only lasting a few miles before having to change, so he ended up ditching the whole set-up.
So we don't have a problem of getting high mileage out of aluminium pistons with today's road conditions do we, but with cast iron able to handle that sort of environment a little longer in the day, Ford and other car builders could at least recommend a engine rebuild after 12000 miles.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Wednesday, April 17, 2013 - 09:41 pm:

Jim what kind of timer? A hybrid mechanical/electronic perhaps? :-)

p.s. I'd recommend 3 aluminums and 1 cast iron. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Wednesday, April 17, 2013 - 10:49 pm:

Hey Jim, You forgot to add some 2 cycle oil to the gas


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Wednesday, April 17, 2013 - 11:46 pm:

The four cylinder horizontally opposed I believe is inherently balanced. The in line four cylinder is inherently unbalanced.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Thursday, April 18, 2013 - 12:54 am:

Some things to think about!

1. In a reciprocating engine the pistons go from zero speed at the top dead center and bottom dead center to the maximum speed when the crank shaft is at 45 degrees to the bore center line.

2. Between top and bottom dead center the pistons accelerate and decelerate.

3. In a 4 cycle engine the piston rod is in compression most of the time – the compression stroke, the power stroke, and the exhaust stroke. It is in tension during the intake stroke.

4. It takes energy to accelerate or decelerate a piston.

5. When the mass (weight) is high it takes more energy to change the speed of a piston than when it is low. (F=M*a)

6. I.e. Light weight parts take less energy (force) to change speed.

7. When switching to lightweight pistons you need to remove some of the crankshaft counter weight to keep things balanced.

8. Aluminum melts at a lower temperature than cast iron. 660 C vs 1200-1540 C

9. A normal Model T doesn’t care about any of this – but when the speed demons show up anything can happen.


As for differences in piston speed during the upper part of the stroke and lower –
The only times they can be different is if the center line of the piston travel (bore) does not pass thru the crankshaft main bearing center line or if there is an offset in the connecting rod at either end.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Thursday, April 18, 2013 - 01:17 am:

Fred said: "1. In a reciprocating engine the pistons go from zero speed at the top dead center and bottom dead center to the maximum speed when the crank shaft is at 45 degrees to the bore center line."

Not true. Maximum speed is somewhere above the middle of the bore due to rod angularity.

and "4. It takes energy to accelerate or decelerate a piston."

True, but all energy is conserved. It is either returned to the system as momentum or dissipated as heat.

and "5. When the mass (weight) is high it takes more energy to change the speed of a piston than when it is low. (F=M*a)"

Your formula is correct, but your statement is not strictly true. It is true for any given rate of acceleration.

and "6. I.e. Light weight parts take less energy (force) to change speed."

same as above.

and "9. A normal Model T doesn’t care about any of this – but when the speed demons show up anything can happen."

T's don't care about anything. Some of the folks that drive them do though.

and "As for differences in piston speed during the upper part of the stroke and lower –
The only times they can be different is if the center line of the piston travel (bore) does not pass thru the crankshaft main bearing center line or if there is an offset in the connecting rod at either end."

Not true, as I explained to Seth above.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Thursday, April 18, 2013 - 01:57 am:

A couple points I have not seen on this thread.
One of the reasons that iron pistons were used early in automobile days was that casting aluminum was still somewhat experimental. Franklin automobiles were built by an early day aluminum casting company. That was why they used so much aluminum and most other companies did not. Some early automobiles are difficult to restore because the aluminum castings were poured too hot or too cold and were too brittle even when new. Many automotive engineers in the early days did not consider aluminum an appropriate material for such a stressful application as a piston.
In later years, they switched to aluminum (slowly as humans usually do) in spite of aluminum's higher initial cost, in part because its total cost is less than cast iron because the casting costs are less, and the machining costs are much less.
Did I adequately answer a couple questions asked above?

As with many things, there are trade-offs. One thing improves this point, worsens that point. The reciprocal motions alone, high rpm versus low rpm, are worthy of a master's thesis in engineering. Even though it was probably already done nearly a hundred years ago.
I read many pages of debate in the pre1900 Horseless Age Magazines on the subject of steel versus iron for cylinder construction. My early gasoline carriage has a steel cylinder, which I thought was odd, till I read the many articles. I read much of six years of Horseless Age Magazine publications. We on this forum have nothing over the early experimenters and engineers debating the advantages of this or that to build a better automobile.

The weight difference between aluminum and iron pistons is not as simple as it would seem.
I, too, weighed them and compared them. The aluminum pistons were heavier. HOWEVER!!! That was thirty years ago. For a while, the only aluminum pistons being made for model Ts were sand cast, not die cast. The skirts were about twice as thick as the iron pistons and the head was about three times as thick! They were heavy! Most pistons made for model Ts since have been a little better(?).
To compare the weights and have it mean anything, you need to do a comparison between a common standard late iron piston and a specific aluminum piston from a verifiable source. At least they are a bit lighter now. That was when I started using cast iron pistons.

Another factor not previously mentioned that reduces the difference between iron and aluminum pistons is weight mitigation through cylinder drag.
Enough said, at least by me. If I were going to write a master's thesis, I would have done it years ago.

Cameron W!
Thank you for this thread, even if it didn't go how you wanted it to. I liked your original question. However, what came about has been very fascinating for me to read.
About two thirds of the model Ts I have had used cast iron pistons. About one third had or have aluminum pistons.
Cars with iron pistons included several that performed very well. A race car I had with iron pistons was driven well over 75mph and passed Rajos and Frontenacs going up hill in spite of the fact it had a Ford iron head. My center-door was twice clocked at 55mph totally stock, gearing and all.
Drive carefully, and enjoy, W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Thursday, April 18, 2013 - 02:03 am:

I agree with Tom's assessment of Fred's comments.

Another way to think about the piston speed being different at the top of the stroke is to do a little trigonometry. If you calculate the piston position when the crank is 90 degrees from TDC you will find that the piston is about 2.3" down from TDC and 1.7" up from BDC. Given that the engine speed us constant, the piston coming down from TDC had to travel faster then the one coming up because because it travels more distance in the same time.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Thursday, April 18, 2013 - 09:13 am:

In the FWIW category here are the weights of Al pistons I purchased in November

New Aluminum Pistons (Lang's) .030 over
----------------------------------------

Weights

Al 576g, 578g, 580g, 582g average = 579g

(Old CI pistons (did not save individual weights) = averaged 1134 g each)

The original CI pistons were almost twice as heavy (1.96 x)


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Thursday, April 18, 2013 - 10:31 am:

Tom,
and "5. When the mass (weight) is high it takes more energy to change the speed of a piston than when it is low. (F=M*a)"

Your formula is correct, but your statement is not strictly true. It is true for any given rate of acceleration.

Remember that each piston accelerates 4 times for every revolution.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, April 18, 2013 - 10:42 am:

Each piston accelerates and decelerates twice for each revolution.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Thursday, April 18, 2013 - 11:04 am:

Royce,
Acceleration is a change in velocity, whether it is speeding up or slowing down, but your point is taken


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Thursday, April 18, 2013 - 11:52 am:

A.G.B. said:"Remember that each piston accelerates 4 times for every revolution."

And your point is?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Thursday, April 18, 2013 - 12:05 pm:

It would seem to me that any difference in performance between iron and aluminum pistons would be pretty minimal.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Thursday, April 18, 2013 - 01:26 pm:

Tom,
I was making sure you were not talking about the acceleration of the car. But I do have a question about this statement' "but your statement is not strictly true. It is true for any given rate of acceleration." It seems to say it is not completely true, only true for any given rate of acceleration, but if it is true for any rate, wouldn't it be true for all rates?
Best
Gus


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, April 18, 2013 - 03:11 pm:

Cameron,

The performance difference is substantial, obvious and in the favor of aluminum pistons. You will have better acceleration, higher top speed, and less vibration with aluminum pistons.

Even more important, regardless of which piston used, is the need to balance both the engine and transmission. The engine components need to be balanced both static and dynamic.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Thursday, April 18, 2013 - 03:24 pm:

Royce,

I'm in charge of keeping 10 Ts running at the museum. The best one for acceleration, performance, and smoothness is the Wreck, which I believe you have seen before. It's unrestored and hadn't run in 65 years. It has far more power than a T should, and runs smooth as silk! And it's running iron pistons! I've had it up to 40 on the runway, and was scared to go any faster, but it had lots of throttle to spare.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James Baker on Thursday, April 18, 2013 - 03:31 pm:

My 22 touring cut-off has the original iron pistons. It runs nice and smooth. It's the only Model T I've ever driven or sat in, so I can't really compare it to another one.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Thursday, April 18, 2013 - 03:53 pm:

A.G.B. asked"but if it is true for any rate, wouldn't it be true for all rates?"

Yes, you and he are correct. Sorry.

Cameron asked: "It would seem to me that any difference in performance between iron and aluminum pistons would be pretty minimal."

All things considered, I think aluminum is better. Especially in the area of vibration and bearing stress. As far as top speed and acceleration, not much difference. I have used cast-iron in the Montana 500 and finished in the top 3 several times with them. When I pulled them out and put in aluminum pistons there wasn't a huge change that I noticed. The first year after I pulled the cast-iron pistons and put in aluminum I came in 4th - same car, same engine, same everything except for the pistons.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve osborne on Thursday, April 18, 2013 - 05:02 pm:

wow, good read, thanks guys.

I'm making things up here so when your done laughing feel free to straighten out my thinking.

Back to the comments about tractors and diesel engines being cast and heavy.

Cast. heavier, more energy to get moving, therefore more energy to slow down, thus torque. Less Rpms, less friction, less heat?

aluminum, lighter, less energy to get moving, less energy to slow down thus less torque? More Rpms, more friction more heat?

If I want a model T to chug along heavy pistons.

If I want a model T to race at high Rpms and perform light pistons?

obviously there is not a great amount of difference from one model t engine to another but from a diesel to a formula one there is one is heavy for torque one is light for high performance. So what do you want your model T to do chug up a hill with little change in speed, or race up a hill while losing speed?

like I said making it up.

oz


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Thursday, April 18, 2013 - 05:45 pm:

Steve, that is the theory. As far as I'm concerned it is just a theory. May be a bunch of hogwash though.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Thursday, April 18, 2013 - 06:32 pm:

My father is a mechanical engineer and designed engines, including top-fuel drag racing engines as well as other racing engines in general for 40 years. I have great respect for his opinions and he posed an interesting point.

In a 4 cylinder, the force of accelerating one piston is exactly equal to the force of another decelerating that is 180 degrees off of the first one. Thus, your net forces are equal, whether using iron or aluminum pistons. You'll see no benefit in performance from using either one. The problem seems to be is that we keep analyzing each cylinder individually, when we really need to look at the engine as a whole. What one piston does, another counteracts it and balances it out.

This, however, does not include harmonic vibrations that are inherently present in 4 cylinder engines, which has nothing to do with the weight of the pistons. The only way to quell those is to use a heavier flywheel, and I think that we can all agree that that is one of the T's strong points!

However, if you use iron pistons, it can put more stress on the babbitt and crankshaft due to the extra weight, but as much as you might think.

Now on an engine such as a V-8, the weight of the pistons must be matched to the counterweights on the crank. It would be a terrible idea to put lighter or heavier weight pistons in it than those that it originally had, as vibration will increase greatly.

Long story short, aluminum pistons will be easier on the crank and babbitt, especially at higher RPMs, just a little bit, but iron pistons won't make any sort of difference in acceleration or torque.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Thursday, April 18, 2013 - 07:16 pm:

Cameron,
About, "..iron pistons won't make any sort of difference in acceleration or torque".
I believe that the power and torque will be unchanged with cast iron but the acceleration or rate of change of engine RPM will be less with the heavier pistons. Kind of like a heavier flywheel, total power will be the same but acceleration will be less. How much difference? I don't know.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Thursday, April 18, 2013 - 09:06 pm:

Jim,

I suppose that there would be slight difference in the engine's acceleration if you're in neutral, but when driving, you won't notice.

It would be less than the difference of having flywheel magnets vs. oil slingers.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, April 18, 2013 - 10:50 pm:

False. You will notice. Aluminum pistons offer a significant performance advantage and will give you a longer lasting engine, ie more miles until the next overhaul.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Friday, April 19, 2013 - 12:04 am:

Royce,

Say what? Forces in a 4 cylinder engine cancel out one another. If you do some simple physics, you can see that for yourself. Aluminum pistons will give you a slightly longer lasting engine, but there is no significant performance advantage whatsoever. Please do the math before you post.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, April 19, 2013 - 07:02 am:

Cameron,

The math is simple. Your understanding of it may be your problem.

Reciprocating weight in any internal combustion engine is lost energy. Any reduction in reciprocating mass (weight) directly reduces the amount of energy needed to rotate the engine whether running or being turned by the flywheel. Reciprocating mass is not imparted to the flywheel, it remains constant because each reciprocating part must start and stop during revolution of the rotating mass.

Did you sleep through grade school physics? This is Newton's first law. Look into it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Friday, April 19, 2013 - 10:56 am:

Cameron,

Royce said: "Reciprocating weight in any internal combustion engine is lost energy."

Not strictly true, as we have been discussing this entire thread. Energy is conserved so whether the energy used to overcome the inertia of the heavier piston is reused to propel the car or wasted as heat is a matter of whether it is dissipated mostly as positive or negative feedback (and how much is lost to friction). I aver that the friction of a heavy or lighter piston is pretty much a wash, so the question comes down to feedback. My theory was that the momentum was reused as mostly positive feedback. I explained above how I thought this could happen. I can't prove that this is so, but it makes sense to me and seems to correlate with my and others real world experiences with cast-iron pistons. Why Royce, whom I believe to be a good guy and quite knowledgeable feels the need to insult you is beyond me.

Also Cameron, you said "Forces in a 4 cylinder engine cancel out one another." It is true that all forces eventually offset, but not at any given moment. This is due to rod angularity as we discussed above. Not that this matters as to your point.


Top of pagePrevious messageNext messageBottom of page Link to this message  By A. Gustaf Bryngelson on Friday, April 19, 2013 - 11:04 am:

Tom,
If all four pistons have to be started from a dead stop at the same moment, I can not see where there is any conserved energy in reciprocating parts, at every 1/2 revolution all reciprocating parts are at a standstill.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Friday, April 19, 2013 - 11:36 am:

A.G.B.,
You are correct that it takes more energy to get all 4 heavier pistons to move from a dead stop but that very same energy (less any friction) is put back into the system when those pistons are stopped and the end of the stroke. It acts just like a flywheel but not nearly as mechanically efficient because it the heavier pistons puts more stress on the rods and crank bearings.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, April 19, 2013 - 11:39 am:

I have not insulted anyone, only offered knowledge Tom. This is elementary school level physics.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Friday, April 19, 2013 - 11:43 am:

Energy is conserved. Not just a good idea, it is the law.

The energy imparted to the piston from combustion (or from the crankshaft) will cause the piston to be in motion. Once in motion, the piston will want to stay in motion. Friction will slow it down, but not all of the energy is dissipated as frictional heat. I postulate that the remaining energy is given back to the crank shaft through the rod as positive feedback since it is in phase with the power stroke. In other words, the crank is not using its energy to try to slow the piston, the piston is using its stored energy (momentum) to try to push the crank.

In more other words, the crank wants to slow down, but the piston's momentum won't let it.

A frictionless motor would continue to turn forever once you set it into motion. Energy is always conserved.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Henry Petrino in Modesto, CA on Friday, April 19, 2013 - 11:47 am:

Tom,

I think you'd also need to eliminate gravity to get a "zero friction" engine to continue to turn forever.....


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, April 19, 2013 - 11:48 am:

If a piston were a projectile shot from a slingshot it would remain in motion until its energy was dissipated.

However, a piston connected to a crankshaft needs to reverse direction every half revolution of the crankshaft. This motion is lost energy. It is the same amount of energy whether the car is running or you are rotating the crank by hand. It neither powers rotation, or transfers to the flywheel. It is energy that is lost.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Friday, April 19, 2013 - 11:52 am:

Royce, in my book "Did you sleep through grade school physics" offers no knowledge. Maybe Cameron wasn't insulted, but I didn't appreciate it.

Royce said: "This is elementary school level physics."

This may be true, but there are several smart guys that see it one way and several smart guys that see it another. One group is probably right and the other wrong. I find it helpful when people show me where I'm wrong and why they think I am wrong. Just telling me I'm wrong is no help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Friday, April 19, 2013 - 11:55 am:

Royce said: "It neither powers rotation, or transfers to the flywheel."

Why not? If the piston is trying to go faster than the crank will let it, why wouldn't it impart its energy into the crank?

Where would its energy go otherwise?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, April 19, 2013 - 11:56 am:

Tom,

I am just trying to help you understand why you are wrong. I am not succeeding.

In any case we know that when we build racing engines, to make the most horsepower we reduce reciprocating weight any way that is within the budget because it increases horsepower.

Reducing rotating mass does not increase horsepower, but it does improve acceleration. In the case of drag racing engines much attention is placed on reduction of both rotating mass and reciprocating mass.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Friday, April 19, 2013 - 12:41 pm:

Royce said:"I am just trying to help you understand why you are wrong. I am not succeeding."

Because you haven't specifically said where you disagree with what I've said.

Royce said:"In any case we know that when we build racing engines, to make the most horsepower we reduce reciprocating weight any way that is within the budget because it increases horsepower."

Does it really, or have you read this somewhere and assume it is true?

Are you sure it isn't done to reduce load on bearings and such? Are you sure it isn't done to increase acceleration? Are you sure that you don't just believe it because you read it somewhere it "seems" right?



While I'm asking questions, I'll repeat a couple I've asked before that you haven't addressed.


If the piston is trying to go faster than the crank will let it, why wouldn't it impart its energy into the crank?

Where would its energy go otherwise?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, April 19, 2013 - 02:51 pm:

Cameron,

I use a dynamometer or a race track to test my engines. But this stuff is not my idea, it is as old as Sir Isaac Newton. A lighter anything takes less force to accelerate or decelerate. This is why when we build racing engines we use the lightest pistons we can afford, the lightest pushrods, the lightest connecting rods, etc.

It is true that lighter pistons or rods exert less pressure on bearings, thus giving greater longevity between overhauls. Less stress on bearings also yields more horsepower.


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep NZ on Friday, April 19, 2013 - 03:07 pm:

i thought i gave a comprehensive explanation of this already? The cast iron pistons may be giving the illusion of smoothness because they are effectively exchanging one form of vibration for another, Illusion would possibly would be eliminated if the crank was twice the diameter.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Friday, April 19, 2013 - 05:23 pm:

Kep are you referring to the post of April 17, 2013 - 03:19 am:?

I'm not sure I understand exactly what you are saying, but this seems wrong to me.

"The cast iron pistons in theory are taking the extra energy they helped save during compression cycle to make them reciprocate."


The one thing no one seems to agree with me on (except perhaps Cameron) is that a reciprocating force can put stored energy back into the system. Pendulums do it all of time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, April 19, 2013 - 05:47 pm:

A piston is not a pendulum. It is not allowed to swing as far as it can until the energy is expended, then swing the other way. Also, a pendulum is a regulator in the clock. It does not store energy at all. The energy is stored in the clock's weight.

That is simply a non analogous comparison Tom.


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Friday, April 19, 2013 - 09:04 pm:

I don't usually get in these discussions but I can say for sure that my old 24 tudor pulled these hills around here better with the cast iron pistons. You won't convince me other wise because I know what I know, none of you were there! Have fun, KB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Friday, April 19, 2013 - 09:53 pm:

First off let me state that I am not a learned man. I have never been to the University, but I believe I understand what I'm talking about and won't back down when I think I'm right. However, I try to keep an open mind and will admit when I'm wrong. I am willing to learn so feel free to correct me.


Royce said:"A piston is not a pendulum."

True enough. I never said that it was. I said that a pendulum was a reciprocating force that put stored energy back into the system. If you had a hypothetical frictionless pendulum and used x amount of energy to get it swinging, it would always have x amount of energy in it. Which dove tails nicely into your second sentence.

"It is not allowed to swing as far as it can until the energy is expended"

When a pendulum stops at the top of its travel, it has not expended all of its energy. Most of the energy (except that lost to friction) is still there. It has just changed from kinetic energy to potential energy. At the bottom of its stroke it is all kinetic and no potential, at all other times it is a mixture of the two.

Then "Also, a pendulum is a regulator in the clock."

It can be. True enough.

Then "It does not store energy at all."

False enough. It stores the energy imparted to it by the escapement for one cycle, then trips the escapement and gets a little boost and so on.

Wow - talk about thread drift!

Then "That is simply a non analogous comparison Tom."

I never said it was a good analogy, although there really are some similar concepts involved.

Here is a thought experiment. Assume that you have two pistons hanging from a string. One piston is cast iron, one aluminum. The cast iron piston has twice the mass of the aluminum piston. Assume there is no friction in the system. Lets say that you apply X number of joules of energy to each piston to get them swinging. Assume that 100% of that energy was transferred to each piston.

Question: Which piston pendulum would have the most energy stored in it?

Royce, I have addressed all of your points. Why won't you answer the questions that I posed above?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Saturday, April 20, 2013 - 12:17 am:

WOW-- I must be missing something here.

If the centerline of the bore goes thru the centerline of the crank and the crank shaft is rotating at a constant speed - the speed of the piston on the first 50% of the stroke and the last 50% of the stroke has to be a mirror image.
The length of the lever arms change (unless someone has figured out how to change the crank throw and piston rod length while things are rotating)

As for piston speed - The distance of the crank to the centerline of the bore increases up to 45 degrees and then decreases due to the angle of the con rod. When the angle is 0 (TDC and BDC) the linear movement of the piston is zero. Then as the angle increases the piston speed is proportional to the angle. The max angle is reached when the crank is at 45 degrees thus the max speed is reached. Long stroke motors have higher piston speeds at the same RPM than short stroke motors because the leaver (crank throw)is longer.



As for mass and acceleration - It takes less energy to accelerate a low mass - One of the first things racers do is put lightened flywheels on their vehicles to enhance acceleration. (it take less energy to keep things spinning that to get it spinning -I.e. acceleration) Most street cars have a relatively heavy flywheel to store energy and dampen vibration. Pistons, connecting rods, crank shafts, flywheels, are all part of the mass that have to accelerated and decelerated. Make them lighter and it takes less energy.



Of course this, degreed mechanical designer with additional credentials in materials might have forgotten a few things over the years.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Saturday, April 20, 2013 - 12:41 am:

Fred, you are missing something.

Quote"If the centerline of the bore goes thru the centerline of the crank and the crank shaft is rotating at a constant speed - the speed of the piston on the first 50% of the stroke and the last 50% of the stroke has to be a mirror image."

It does not and is not. I thought that I explained it really well above. Here is a link that explains it in better detail:

http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm

That makes most of your second paragraph wrong.

Of course it takes less energy to move a small mass than a large one. I think everyone agrees on this.

No offense meant to anyone, but I'm beginning to think it is a mistake to try to talk about this stuff on this forum.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Saturday, April 20, 2013 - 01:22 am:

Tom,
That is a good link if you can get folks to read it. Here is the chart on piston speed:



Fred D., Note that the maximum piston speed is at about 75 degrees ATDC and on average it travels faster on the top end then the bottom end. This will vary some based on the relationship between the crank throw and the rod length but it is close for a T.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep NZ on Saturday, April 20, 2013 - 02:23 am:

My point was if the pressure reduces in the combusting chamber there will be less force applied to the crank near the bottom of the stroke and that would be when another cylinder was reaching full compression. If the pistons weighed more they would have more momentum to overcome the compression. The problem is they would put more force on the crank when they did have to change direction. Hopefully i will be able to test this soon as i am trying to assemble a cast iron piston engine.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Saturday, April 20, 2013 - 07:00 am:

OK got it!

1 I misspoke about 45 degrees when I should have been saying 90 degrees. Must have been a brain cramp!

2 the article explains that the effective length of the con rod changes between TDC and BDC (called dynamic shortening) based on the con rod to stroke ratio so the length of the levers do change. This means that the piston has less time to accelerate than it does to decelerate so the max speed is before 90 degrees

3. See I am getting smarter Getting the link to the explanation helps


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