Light Rods vs Heavy Rods

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Model T Ford Forum: Forum 2015: Light Rods vs Heavy Rods
Top of pagePrevious messageNext messageBottom of page Link to this message  By John T. Tannehill III, Hot Coffee, MS on Thursday, November 12, 2015 - 09:18 am:

I was just speaking with a friend concerning the earlier (heavy) Rods and the improved light weight ones. If you are using aluminum Pistons does it really matter? I understand the idea of total weight reduction but does it really have a major effect on the total performance. It seems a real waste that heavy rods are not being used as we try to find light weight ones for our refresh/rebuilds. Forum what are you thoughts, expertise?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Thursday, November 12, 2015 - 09:40 am:

They should work very good if you're not into racing - and be authentic on a pre 20 car. But there were about 12 million x 4 "light" rods made compared to about 3.5 million x 4 heavier ones, so it should be easy enough to find the lighter and later version? And the vendors has an exchange system for the light rods only.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Harper - Keene, NH on Thursday, November 12, 2015 - 09:53 am:

To my knowledge none of the re-babbitting providers will repour a heavy rod. You will have to do that yourself. And then bore it to size.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Keith Townsend ; ^ ) Gresham, Orygun on Thursday, November 12, 2015 - 10:16 am:

John-
It seems to me that if you are doing an engine rebuilt (unless you want bone stock) it would make sense to use the best of what is available. After all, how many times do you anticipate doing a rebuild?

The Ford Service bulletins say the new rods were 6 to 7 ounces lighter, and I know of no way to determine the actual performance difference between an engine rebuilt with light rods -vs- an identical engine rebuilt with heavy rods. I don't believe Ford said there was any performance difference. The new rods were probably just a cost cutting measure.

The difference between aluminum pistons and iron pistons is about 5 lbs -vs 11.5 lbs. Add in the difference in rods and it is another pound and a half. I think every little bit helps.

However, what may be more important is getting them balanced. Oh and a straight pan...

About 35 years ago I had the glass in an oil sight gauge break and I lost rod #4.. I checked the journal and ordered a replacement rod from Bob (Sr.) I replaced it and thought no more about it. Ten to fifteen years later when I became a member of the two-piece crank club and completely rebuilt the engine, I was surprised to find the rods did not match! I had the original 3 heavy rods and the one rod which I had replaced was a light rod. Back then I don't think I even knew there was a difference!

Are you having problems finding light rods?

: ^ )

Keith


Top of pagePrevious messageNext messageBottom of page Link to this message  By ROBERT BERGSTADT on Thursday, November 12, 2015 - 10:20 am:

I have a few sets of heavy re babbitted rods in stock, Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Thursday, November 12, 2015 - 10:51 am:

True you can't use heavy rods as cores when you buy from the suppliers but if you are having your rods done by someone else, a rod is a rod, they should be able to do them as well.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Thursday, November 12, 2015 - 11:32 am:

One of the T's I bought had 3 different kinds of rods in the engine. I couldn't tell the difference until I got ready to work on the engine. It seemed to run smoothly just the way it was.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Georgetown TX on Thursday, November 12, 2015 - 11:38 am:

Lighter reciprocating components give you "free horsepower" in the vernacular of engine rebuilders. Each of those heavy rods must come to a complete stop and then accelerate to speed twice for each engine revolution. Anything that you can do to reduce the weight of pistons, rods, and valve train components will result in a smoother engine that has more horsepower, more torque, and more engine operating time until next rebuild.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Thursday, November 12, 2015 - 11:46 am:

From what I have read and seen there were three basic type rods made: heavy, medium and light. The medium rods I have seen look close to the light weight rods but just a little beefier. There seems to be a lot of those out there. The mediums weight rods may be included in the count for light rods because I sure don't see that many of what we call the light rod out there, or someone is hording them.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Layden Butler on Thursday, November 12, 2015 - 11:56 am:

The power used in acceleration of the piston assembly is recovered when the piston is slowed down. Life of the engine due to stress and wear certainly is a factor of weight.
Not mentioned but related, flywheel weight also does not affect horsepower but does factor into acceleration.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, November 12, 2015 - 12:02 pm:

Layden,

Actually what you are saying is a common misconception. A heavier flywheel, being heavier, takes more power to accelerate to speed, or to slow from speed, or to maintain at speed. These are elementary physics rules. Same applies to the rods, pistons, and valve train components. You cannot change the laws of physics.

A heavier flywheel or rotating (non - reciprocating) mass can be better for vehicle acceleration depending on the amount of horsepower / torque and the vehicle weight.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Thursday, November 12, 2015 - 02:21 pm:

Ok, how about someone posting photos of the three kinds of rods, as some folks here haven't seen the insides of their engine--yet!!
:-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, November 12, 2015 - 03:22 pm:

The heavy rods are found in the Canadian engines as late as 1916, I've done some for other club members but I would think twice on using them myself, I drive my T's hard, besides being harder to pour they hold a lot more babbitt and then add a ground shaft as well, in my opinion you end up with far too thick bearing and easier to flog out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erik Barrett in Auburn Ca. on Thursday, November 12, 2015 - 05:30 pm:

There is no good reason to use the heavy rods. You can't see them in use, and they add load to the crankshaft. The best uses for them are concrete reinforcement and metal sculpture.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie Spokane, WA on Thursday, November 12, 2015 - 05:49 pm:

Actually, Layden is right and Royce is wrong. A heavier flywheel does take more energy to get to speed, but it gives it all back when it slows down. All else being equal, it does not take more energy to maintain the speed of a heavy flywheel than a light one. It is called conservation of energy, one of the fundamental laws of physics.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john kuehn on Thursday, November 12, 2015 - 06:17 pm:

If Ford went with the lighter rods in the later T's I think that's good enough for me whether to use them or not. He must have done it for a reason.
But if your a complete purist and want to be pure as possible that's up to you whether to use them.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Walt Magas on Thursday, November 12, 2015 - 08:10 pm:

Here's a photo of three rods used on model T's.
From left to right 1) heavy rod 2) lightweight rod and 3) late 1927 "X" rodRods


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, November 12, 2015 - 08:49 pm:

Tom,
You just said exactly what I said.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie Spokane, WA on Thursday, November 12, 2015 - 09:19 pm:

Royce said:"A heavier flywheel, being heavier, takes more power ~ to maintain at speed."

This is cut and pasted (and edited for content) from your post. It is not what I said. All things else being equal, it is also not true.

Everything Layden said above, however, is essentially correct.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Friday, November 13, 2015 - 03:48 am:

There were several versions of the heavy rods before 1920. Early 1909 on the first 2,500 engines may have had a different solution for the piston pin with a bronze bushing in the rod and an integrated dipper. Following that in early 1909 was a heavy rod with the typical T's piston pin clamp:

r1 r2

Later in 1909 and 1910 the dipper was ground off and the babbitt got beveled at the parting line instead so the oil fog in the crankcase could enter there. Then the rod got changed again in 1915 - a little lighter and the babbitt was now 1/16" thick instead of 1/8". The really light rods was introduced 1920.

rods

Pictures from earlier rod threads at the forum.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Eric Sole - Castelldefels (Spain) on Monday, November 23, 2015 - 03:54 pm:

Are the earlier "heavy rods" less prone to twisting and bending than the later "light rods"?

Just wondering.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Monday, November 23, 2015 - 08:24 pm:

Rods don't twist, and bend inside the engine.

They need alignment after the machining operation, as there is not a machine made that will bore them, ready to install.

Use the light rods!

Herm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Monday, November 23, 2015 - 09:27 pm:

"Rods don't twist and bend inside the engine."

Many things can cause a rod to bend, twist and or break for a variety of reasons.

Fatigue.
Especially in older engines as the rods have done thousands of times a minute, compressed and stretched.

low on oil.
Piston grabbing or wrist pin locking up.
Running too hot. Same thing, piston lock, pin etc
Hydrolock. leaking head gasket etc.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Tuesday, November 24, 2015 - 12:17 am:

Frank, a rod going through the block can do it also, but again that was not the question.

You will just have to save all your brilliance for another time if somebody asks the right question.

Herm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Tuesday, November 24, 2015 - 01:43 am:

My brilliance is well above you pay grade Herm!

Eric.
To relate to your question in full, the answer is yes,
Less prone to twisting and bending than the lighter ones.
As in a engine malfunction they can take that little more and in the case of a badly tuned engine, also better, a heavier rod is also more desirable for lower revving and higher torque engines, but the design of the early T rods of the thicker babbitt would be a de-siding factor in a choice of using them.
\


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Tuesday, November 24, 2015 - 01:54 pm:

Well Frank, as a company that has rebuilt over 30,000 Model T rods, heavy and the later lighter rods, and checking each one for twist, bend, and offset I can say that the majority of lighter rods, are stronger then the earlier heavy rods.

The only variance being in what company made them for Ford.

Now I know being that you always argue that your milling machine will machine rods straight, and there fore don't have to check alignment, that you have not had any experience in mass bearing rebuilding or even on a small scale.

Again, your paragraph out of some bodies book has nothing to do with what Eric asked.

Try this Frank, out of my book, The Fast Ford Handbook, this does answer the question asked.

Nothing else to say about it, Frank, but you can just keep on with your babbling.

Herm.



Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Tuesday, November 24, 2015 - 02:52 pm:

I don't disagree at all with that book Herm, if I was looking to make a T do 75mph!!


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