Rebuilder out of business and I know why

[dean from bozeman]

For years I had wanted to restore several Model A's. So when I had the chance I had an engine rebuilt by a man who at the time had a good reputation. Well as time went on there were other priorities and the engine wasn't used.

Fast forward to last Fall: A Model A that I had needed an engine so I put that rebuilt one in. It took some doing but we did get it going and it ran fine...that is until we turned it off. When that happened we couldn't get it restarted until it almost totally cooled down.

We measured the bore and the pistons. There was less the .002 clearance. The pistons were .030 over. They were replaced with .020 pistons and the engine ran well until it was turned off. The same problem. It had to totally cool down before it could be restarted. It was better than before (less time to restart it) but still not right.

Now I must say that going to a .020 piston, I thought it would be best to put the .030 rings back in so it wouldn't be too sloppy.

We checked the clearance on the center main and it was less than .002.

When the engine was rebuilt the man said that he had built it "tight" so that when it finally broke in it would be a fine engine for a long time. Naive me. I wondered why a guy wouldn't build it to be at its best from the get go. But I figured he knew what he was talking about.

Engine rebuilders live hours from me. So I can't just drive over and talk to them...yet. So I "drove" to Fordbarn and want to get your ideas first. Any ideas, suggestions, experiences are welcomed and appreciated.

Thanks.
Dean

[ronn]

Just a thought........... synthetic oil keeps motors looser then reg oil- the reason I know is my buddy used to work on school buses and they often came in bone dry and never froze. I would try a 20 weight............. for break in.

[700rpm]

Dean, are you asking for the name(s) of rebuilder(s) we trust? Do you want to take the engine to somebody and make it right?

[C26Pinelake]

how many years from time it was a rebuilt until you installed it. How many years ago was it rebuilt ? Wayne

[J Franklin]

I would not be worried about .002 on the bearings, but those undersize pistons should cause a bit of slap.Maybe try 5-30 oil for a few thousand miles.

[40 Deluxe]

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Need more info. Is the engine seized and unable to be turned over after shutdown? Or does it crank OK but just doesn't fire up? Any unusual noises, leaks or blow-by while it is running? Does it run smoothly? Does it have normal power? Those .020" pistons are going to be sloppy no matter what rings you used. Rings do not take any slop out of a piston! What is the ring gap set at? What did the cylinder walls look like after the initial teardown? Any scoring or scuffing? If so, near the top of the cylinder, or near the bottom?

[larrys40]

Probably Herm and James Rogers may comment but I would first make sure you measured the bore accurately with a high quality bore gauge and compared to the pistons. a .002 clearance should be fine, if less then it was probably too tight.
My druthers would be to NOT run undersize pistons but to disassemble and hone the block to the proper piston fit... then reassemble with new rings.

Of course checking for proper clearance on mains and rods as well.
Larry Shepard

[John Duden]

i rebuilt my john deere G, with a 6 1/8 bore and a 9 inch stroke the mainbearings and rod bearings were set at .003-.006, And that is for the 2 inch journals, now factor in heat expansion,
They recomend (for them at least) .004 per inch of bore between wall and piston, for heat expansion.
hope this may help
john

[Mark in MT]

Dean: If I had to bet, I would say that the pistons are swelling up in the cylinders, causing the tightness. Aluminum expands at twice the rate of cast iron, and the pistons gets hotter than the block. I will send you a pm.
Mark Nelson

[aonemarine]

check the depth of the ring grove. if the rings are too wide for the depth of the grove when the piston expands it will wedge the rings into the cylinder wall.

[Tom Wesenberg]

I would do as Larry said.

John, I'm really surprised the large bore and stroke G only has a 2" journal. I'd have thought it would have used about a 3" journal.

[harleytoprock]

When you removed the .030 pistons, how did they look? Any scoring on pistons or rings? Did you check the .030 ring end gaps?

[James Rogers]

40 Deluxe is on the right track. You are probably having a problem with expansion of the pistons tho, I have never had one seize when shut down. I have had pistons that seized or almost did while running. This most often or always happened when I used older split skirt pistons. I always hone to .004-5 for clearance using pistons available from Snyder's. This is to coincide with a ring end gap of .004 per inch of piston diameter or, .014-16. As for the .002 bearing clearance, I always set mine at .0015 -.002 so, .002 is at the top of the range and close to too loose. I have never had a problem with these practices and have many motors running happily.

[George Miller]

The rule off thumb is .001 per inch. The bearings are good, a little on the loose side for a new engine. Pistons are to tight. You need to have the cylinders honed. You could take it to any engine shop and have it honed. Get those .020 pistons out of there it is not going to work.

[James Rogers]

George is correct. Rods 1.500 journal is .0015 and the mains are 1.625 and are .0015 also. He is also correct about the .020 pistons. A recipe for disaster.

[Fullraceflathead]

You can't run .020 size pistons in a .030 bore.
Yes it will run but the pistons are running way to lose and are cast Aluminum.
They will work harden and start cracking sooner or later.
Piston sets are still only $100.00 why risk a total failure later as that's what is going to happen?

[katy]

It took some doing but we did get it going and it ran fine...that is until we turned it off. When that happened we couldn't get it restarted until it almost totally cooled down.

I've seen this happen a few times, it was caused by the rings end gap being too small. Rebuilder said "you don't need to check the gap on new rings, they're factory set".
THAT'S NOT TRUE, EVERY ring has to be checked in it's individual cylinder.

What is the ring gap set at?

Did you check the .030 ring end gaps?

Ditto on what Larrys40 said:

My druthers would be to NOT run undersize pistons but to disassemble and hone the block to the proper piston fit... then reassemble with new rings.

[James Rogers]

Originally Posted by katy

I've seen this happen a few times, it was caused by the rings end gap being too small. Rebuilder said "you don't need to check the gap on new rings, they're factory set".
THAT'S NOT TRUE, EVERY ring has to be checked in it's individual cylinder.





Ditto on what Larrys40 said:

Ring end gap is not set by anything EXCEPT the bore of the cylinders.

[George Miller]

I agree with James .003 in the bore dia. will make much more than .003 in the end gap. Do the math.

[ursus]

Originally Posted by aonemarine

check the depth of the ring grove. if the rings are too wide for the depth of the grove when the piston expands it will wedge the rings into the cylinder wall.

What is the minimum clearance (difference) between the depth of the ring groove and the width of the rings?

I have seen quite a bit of variation over the years, with compression groove depths of 0.160 - 0.210 inches and compression ring widths of 0.160 - 0.180 in width. I have some older Model A pistons that are labeled with a warning that they have shallow ring grooves and are not to be used with rings having a standard width, but it doesn't specify the desired ring width.