OK, Here's the deal. A while back, I bought a rebuilt engine/trans listed here on the Classifieds. The seller didn't rebuild it, but he gave me the name and location of the fellow who did. He also said the engine has new babbit, pistons, rings, valves, etc. -- a complete rebuild. I know a forum member who lives in the same area as the engine builder, so I called him on the outside chance that he might know him. He does know him and said he's a good Model T mechanic and an engine he built should be a good one, so I felt pretty good about going ahead with the deal to buy the engine (which I did).
So over the past 2 days, a buddy and I put the engine into a car. It felt pretty tight, but not too tight to crank (it's a non-starter engine). We hooked a strap to it and pulled it, and it started right up. It runs like a top -- smooth, quiet, and plenty of power for a stock engine.
Yesterday we took it for a drive, and I was feeling great about my purchase. It ran great for about 20 minutes, then gave a loud "squawk" and the engine stopped immediately. The squawk sounded to me like it was metal-to-metal. I pulled the crank, and it wouldn't turn, so I got my trailer and took it back to my shop.
This morning I pulled on the crank and it was fine. After about 5 or 6 pulls, it started right up and ran fine, just like the day before.
I'm thinking that one of the cylinders didn't get bored enough for its piston, and when it got hot the piston enlarged and seized up. We know that the box the new pistons come in says to allow 2 to 3 thousandths of clearance when boring the cylinders, and we know that is not enough clearance. Maybe the fellow who built this one followed the instructions on the box? It runs so well that it must be pretty close to being right, but just a tad tight.
So I'm wondering whether I can drive it for 10 or 15 minutes a day for several days and put enough wear on the components to "wear it in", rather than tearing the engine down and having it honed a thousandth or so. Does anyone have any idea how long it would take to wear it a thousandth?
Let the opinions fly!
I had the same thing happen and found the front cam bearing too tight. My engine ran fine until it warmed up and then screeched to a standstill. Lots of torque on the cam shaft to stop the engine. After cooling it ran fine again for a little while. Luckily I never went above an idle (on and engine stand).
Your "Squawk" could be from several sources. Yes it could be piston cylinder clearance, it could be tight cam bearing as Hal has said or it could be insufficient wrist pin clearance in the piston boss. Pin clearance has been a problem with some of the earlier imported aluminium pistons. You need to find the problem, yes it could wear in or it could wear out. Your choice.
Mike, I rebuilt an engine for a friend a long time ago. It had new pistons in a box and all the other stuff to rebuild it with when he bought the project. I used his pistons without much thought as to quality. (I was younger and dumber then) I had them fit at a local machine shop. He fit them to 3 thousands. Because the machine shop owner said that was plenty for aluminum pistons. When we started the engine, it ran great, but after a few minutes it would start to "labor" and finally stall. Same as yours, when it cooled, it would start and run OK for a few minutes. I tore the engine down and had the pistons re-fit to 5 thousands. After that it would run fine for about 15 minutes and then start to labor. I removed the head, lower pan, and pistons. I then honed them myself, in the car, to 8 thousands clearance. After that the engine never gave anymore problem. I believe my problem was using a "old" NOS set of pistons of questionable material. But as Hal and Jack state, your problem could also be cam bearings or wrist pins. If it is a wrist pin it more than likely will not "fix itself" and just score the pistons or bore. It is not a real hard process to remove the head, lower pan and pistons to check out what is going on. If it is just too little piston clearance, you can "hone them in place. Just use some rags to cover the pan area and trans area. I also slid a piece of cardboard in place under the cylinder I was honing to make sure I did not catch the hone on a rag. I also made a mark on the hone shaft to know exactly how far to go in to the cylinder. Then a real good cleaning after the honing. I did it so I know it can be done. Probably not the best way, but I did not want to pull the engine again. Not wanting to be the bearer of bad news, but a "squawk" is not a good thing, and you probably should at least "check it out" ...
Although I don't usually put anything in gasoline, I would make an exception if it were my engine. 2.5 oz of oil per gallon is about 50:1. Outboard oil would be a logical and cheap choice.
It will smoke and maybe fowl your plugs eventually, but it may help your problem and plugs can be cleaned. Very short runs to begin with (1 mile or so) gradually longer. Cool down in between.
If things are too tight as you postulated, that may save the day.
you might want to get a infrared heat gun ///run for a while and check for hot spots record it and try daily to see if its changing
Mike and Bud, please forgive me, "Marvel Mystery Oil". ??? I just had to.... Where can I get a smiley face with horns .??
All good things to look at, I'll add a few more, there was some time back a bad batch or transmission bushes getting around, brass likes to squawk when locking up, triple gear or the fly wheel drive shaft.
Also some bad engine specs too, like on Mac's site of giving the rings a clearance of, Top .003" tight ring clearances will give you a 20 minute lock up, another thing that is sometimes over looked is when valve seat inserts have been fitted after the re-bore, that distorts the bore wall as well.
Donnie -- I added MMO when I gassed it up. I always do.
You guys can laugh all you want, but "Marvel Mystery Oil" will save the day if it's possible that a little more lube can get you past the problem! I would add some to the crankcase & the fuel, it's worth a shot.(I said if it's possible)
Good Luck and be gentle on it! I also agree with harold's suggestion of a Infrared Thermometer, might help isolate the area of the problem.
Mike, the more I read your description of what happened, the more I think transmission.
Jack up the rear and let it run in top gear and check engine temps etc, IF" after 30 minutes the engine seems ok, do the same with the hand brake on, that will be running through the trans bushes then and see what happens.
If your squawk happen in high gear I don't think your problem is in the transmission. In high the only bearing that is used is the fourth main. All others are just going for the ride.
You have a vested interest in the engine and know your way around an engine, why run the risk of major problems down the road. Take it apart and fix the problem.
A metallic squawk? A thousandth would wear long enough to ruin a good engine.
If 1 piston got tight, that means it galled. That means it looks like the cat got in there and scratched around.
Yes, that could be my 'bad' if in top gear, I was assuming that because of no mention of the full flight lock-up and no 2 tires with flat spots that Mike was stopped or going slow/low. How go's it Mike, what was your driving conditions?
Back in the day when I got to play with antique airplanes, newly rebuilt engines would be broken in for the first hundred or so hours with mineral oil. _The point of it was, the stuff wasn't as slippery as "regular" oil and so, caused opposing parts to "lap" themselves together. _Now, I'm not sure that in your case, trying to wear things in would be healthy for the engine, but if you've already decided to go that route, mineral oil will get the job done in fewer hours—at least in theory.
As an aside, I'm wondering whether the originally published 3-thousandth clearance wouldn't work okay with original, cast-iron pistons, but not with modern aluminum pistons that expand somewhat more when warmed to running temperature.
When you pull it down, check the ring end gap.
Rings with insufficient gap will seize an engine as you describe.
I had that happen after installing a rebuilt engine. It would idle 20 minutes and then stop suddenly.
It turned out to be main bearings too tight.
I should have shimmed them, but it had removable inserts. Was rebuilt by some hot shot place in Sacramento. I took the crank out and had .001" taken off each main. It was still very tight on one of the mains. About .0012" ( one point 2 thousandths) if I remember right.
It never seized again and it was still running last fall after 4 years. The owner never mentioned any problems, so I guess it is OK.
Thanks for the suggestions, Guys. Lots of good ideas there. I've heard and read about engines seizing up but haven't experienced it before this. I started this thread to try to learn from others who have had this happen.
It was running in high gear, but not very fast, when it stopped. Had just finished climbing a block-long moderate hill about 1/2-block before it seized.
Dan -- I had thought about ring end gap too. It might be worth going into the engine a bit just to check that.
Could be mains, could be pistons, could be rings. It just runs so well I hate to tear into it, but that's probably the best course of action.
One trick that impressed me with a line bore was bolting a 2 thou shim under a main cap then try to turn the crank. Not easy! Then switch to a 1 thou shim and do the same. The crank should turn with little effort. When you are working with 1 1/4-to 1 1/2 thou of total clearance you better have good measuring tools and know how to use them.
You said you put MMO in the gas, but was it enough to do any good? A few oz per tank wouldn't help the kind of problem you describe. A quart per full tank would be enough to put a little lube on the cylinder walls (all this assuming i'ts a to tight top end problem)
" I know a forum member who lives in the same area as the engine builder, so I called him on the outside chance that he might know him. He does know him and said he's a good Model T mechanic and an engine he built should be a good one."
Why not contact that engine rebuilder and see what he has to say about it?
I can't do that. He passed away about 2 years ago.
Bud -- I didn't put MMO in the gas to correct this problem; it's just something I do routinely.
Considering what a rebuilt engine would cost you, I think it would be prudent to tear this one down and really define what the problem is. You know the engine must have sat for at least 2 years & machinery usually doesn't like to sit around, especially if it hasn't developed a thick coating of lubricants from long use.
Mike----You did fill the cooling system with water? Check the oil and make sure there is no water in the oil. If it looks clear, there is no problem with that. To me the problem might be the ring gap rather than piston diameter. There is no way you are going to hone the cylinder enough running the engine to get an acceptable fit. Ran into this once upon a time.---Len
OK, Guys -- I bit the bullet and removed the lower inspection plate and the cylinder head. Everything looks fine underneath. Here is what the cylinders look like:
Looks to me like #1 has a bit of a scuff, but it's not deep enough to feel it. All the pistons look pretty snug in their cylinders. I'll remove the pistons tomorrow and see what they and the rings look like.
Most piston - cylinder clearance is expressed in thousandths per inch of diameter. Eg one thou per inch of diameter @ 4 inch piston equals .004. Therefore .003 may be a bit tight
That can happen with a fresh, tight engine. Do as you suggested originally, run it in gradually. Don't overthink it. Break it in, then run it.
Since you have it apart, pull the piston and check the rings for end clearance. Also if you have access to a hone, you might run it up and down a few times. That will remove the scuff and increase the clearance between the piston and cylinder. Check the clearance between cylinder and piston. Should be .004 or a little larger. After you get everything together run it slowly a mile or two and if it doesn't seize up, let it cool and drive around again. Do this for about 500 miles and change the oil. Then it should be ready to go faster.
it looks like a little honing will fix the cylinders but if the rings are scored I think I would replace them. Mike is that the ww1 ambulance?
Pull the pistons and check clearance and ring gap. One or both are too tight. .002-003" is not sufficient for aluminum pistons. I give them .005" at 90 degrees from the pin. People set clearances too tight thinking the engine will last longer when the opposite is true. You should have at least .012" or more ring gap. If you are set up too tight you will destroy the cylinders and/or pistons before they wear in. Give it some clearance while you have it apart. The time to get this fixed is now, not when it seizes up beyond help. A couple thousandths is everything here. Don't want to give bad news, but it's not too late to keep it from getting worse. We have rebuilt many engines that were too tight.
I did this chart a couple of years ago to show how quickly cast iron rings can grow and close the ring gap. And, how the ambient temperature at the time of setting the ring gap should be considered. Simply declaring a fixed ring gap is not enough or you will be relying on luck. Engines that are built in different temperature environments need special attention or compensation during measurements.
In the chart, Set Temp (left column) is the ambient temperature of the shop/engine. Across the top is various cylinder temperatures after running the engine. Where they correspond in the chart indicates the amount of ring expansion.
I know this sounds anal but it shows WHY the ring gap is there.
A regular cylinder hone used to cross hatch the cylinders won't increase the diameter. You need a special hone used for that purpose. Lyle makes a fairly inexpensive one. Use a mill, mill drill or heavy duty hand drill, Eg Milwaukee hole hawg and be careful to get a uniform diameter. And be careful not to go too deep. Otherwise you hit a main boss. It takes some time but can be done with satisfactory results. Use plenty of cutting oil and measure often.
You said this is a fresh motor. One thing that is very concerning is that your cylinder walls don't seem to have any crosshatch pattern- could just be the pictures, but. . . . The vertical scrape marks all the way around the cylinder would indicate to me that you do have a ring problem. Head is off- probably time to pull the inspection plate and pop a piston out.
I see it has .030 over pistons which indicates a rebore at some time in its life, but there appears to be a decernable lip at the top of the cylinders? Cylinder, piston and ring technology has changed greatly over the years it is important that the person doing the work is up on the latest. Machining methods have improved to a point that honing becomes a very technical process. Engine blocks are bored up to a point then ground with fine stones to a final finish in a vertical jig to assure straightness. Measurements are taken at regular intervals in temperature controlled conditions. So to just start hand honing may be a grave mistake.
Okie Dokie then -- I pulled the pistons out today,and here is what I found. All 4 pistons are scuffed near the ends of the wrist pins, right up against the bottom ring. The wrist pins are tighter than they should be on 2 and 4 and will need to be honed. Surprisingly, the ring end gap is fine.
BTW, these are Jahns pistons, apparently older ones which are (were) round, not cam-ground.
(Message edited by coupelet on October 02, 2015)
Buy a new set of pistons, they are old slugs and not cam ground for proper expansion.
Get a new set of pistons. The new ones are much better than the old Jahn's stuff. Cam ground, balanced right out of the box, good finish. Better all around. Most of them are sized to provide correct clearance when the block is bored to size, in your case 3.780". Make sure of the clearance, cylinder shape and taper, and proper crosshatch finish. It will be worth the time and expense.
Definitely follow Erik instructions to the letter, but have your machinist fit each individual piston to a cylinder for proper clearance. They should come back numbered to match the cylinder. Also have each piston pin hole honed for a slip fit of the pin. Do not assume the pin fit is correct out of the box. Buy a new set of rings also.
OK, Here's an update. I decided to follow the good advice above, so I called Mike Bender in Tulsa and he had a set of .030 pistons and rings in stock. So I drove over there on Sunday and picked them up. Mike also straightened a couple of the rods while we were at it. Yesterday and today I put them into the engine mentioned above.
Jack P, the pins fit fine. I always check them though, as you suggested, because I too have run into some which were tight.
After some choke cranks, it started on the second pull! I took it for a spin around the neighborhood and it runs great!
Thanks for your help, everyone.
To add to the first question;
How long does it take to wear a thousandth?
Longer when you want and less when you don't!
Glad that you got it sorted out and are back on the road.