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Question on engine rebuilding

J

John Achmann

Member
Ok my background, been a diesel mechanic for 20+ years. I?m not saying I?m an expert but I?ve been into a lot of stuff. Overhauled many engines with and without experienced mechanics near by. So I?ve installed a new overhaul kit on a D-12 Allis Chalmers. Didn?t have it running for 5 minuets and the piston pins locked up in the pistons. They assembled fine. Was lubed putting together. Connecting rods are in the correct way. Had good oil pressure when it was running. Talked to the piston maker. They tell me it?s my problem and I did something wrong. I?ll admit I?ve messed somethings up but here I don?t know what I could have done. When I do engines I double check all work. It?s the way I was taught. So the question is what did I do wrong so the next kit don?t get messed up?
 
Some engines have squirt holes in the rods that spray oil up into the bottom of the pistons and lube the pins. Did you change rod inserts and they didn't have holes in them?
 
Something doesn't sound right as when the pistons get hot the clearance goes up. Are there holes in the bottom so oil gets to the pins? Did they slide in ok or did you have to drive them in ?
 
I agree. Unless they were driven in they should be OK the clearance should be no more than .0008" to be happy. Jim
 
I got into something like that once on allis 149 ci. had a damaged piston from being cocked in cyl..rod checked straight- some nice person on YT allis site told us 2 rods installed opposite. [sorry can't remember details-but I actually dropped piston/rod assy in the block, sure easy to see!! may or may not apply to your engine---good luck
 
Must be you have dismantled the engine again? Are the pins set right up tight? What's the damage? Are the pistons scuffed badly? Did the pins contact the sleeves?
 
That?s what I?m working on. Had rods in correctly. One and three go one way and two and four the other. Just can?t think or find what I did wrong.
 
If it's prior to "61 it should be a 138ci. On those you have to roll them on their back and rub their belly until their tail relaxes. If it's newer with the 149ci you have to hold them by the tail and scratch their ears until their feet dangle.
 
Did you check piston ring end clearance and side clearance. Especially to the kit spec and not to the A.C. specs?

Years ago at work we went with an aftermarket piston ring and installed to the original specs and we got our lunches ate. I mean ate. I mean in the six figure range.
 
Hello john achmann,

If all the pistons are junk it is a COMMON problem. Either the kit is junk! Or they oil did not get there in time and the pre lube was not adequate. Are the pins and pistons dry? if they are not and plenty of lubrication, sounds like a set of junk parts to me. Hard to prove though. How did you first start the engine?, as it was DRY other then the pre lube. I use a oil pressure tank to pre lube a new rebuilt. Sometimes you can crank the engine on the pre lube, with out letting the engines star,t until you see oil pressure. That works good too. I hate when something like this happens, and have to do it all over again!

Guido.
 
Well since The rod is tight on the pin then I am guessing there is no hole for oil to flow up the rod to the pin. Must be an alignment issue. Either the rod and piston are not true to ech other or the block is not true to the crank. I would doubt the later since the engine has run for decades with the previous parts in it.
 
I also have a prelube tank. Do this to every engine that I?ve rebuilt. Then before I start the engine I remove the coil wire and crank until I see oil pressure on the gauge. Then away we go with the start up. Just makes no sense what has gone wrong. Parts company asked questions and I feel I did everything correct but they say I did something wrong.
 
(quoted from post at 20:21:13 11/08/17) I also have a prelube tank. Do this to every engine that I?ve rebuilt. Then before I start the engine I remove the coil wire and crank until I see oil pressure on the gauge. Then away we go with the start up. Just makes no sense what has gone wrong. Parts company asked questions and I feel I did everything correct but they say I did something wrong.
Click to expand...

Hmmm... Did they have any suggestions for what you did wrong? That's big of them to say you did something wrong and not have anything to back that up. :?
 

I don't know what the spec is or how you measure it but aren't piston holes supposed to be honed if the wrist pin to piston clearance is not adequate?
 
Never heard of such a thing. It must have been fun trying to get it back apart. As those run with virtually no lube, I can only guess the pistons were made out of the wrong material. I assume you used the original pins.
 
(quoted from post at 11:08:41 11/08/17) Sorry I didn?t mention the rods clamp to the piston pin. So no bushing there.
Click to expand...

I am thinking the problem could have occurred when the rod was clamped onto the piston pin. Perhaps the pin was not designed for the clamp load and distorted. In this case the pin to piston fit would have been out of spec. The distortion could have occurred after the engine was started. Might compare the new pins with the ones removed, how does the wall thickness compare.

Just a thought - I am not an expert on these engines by any measure. Good luck!
 
To me this sounds simple. A piston pin has to pivot either at the rod small end with a bushing that is splash lubed, or drilled for pressure lube. Other way is the pin is either clamped or pressed to the rod small end and the pin pivots in the piston. Never seen one like this lubed anyway but by splashed oil. You have pistons that are not drilled at the pin holes. These pistons are made to pivot at the small end of the rod. My guess,,, wrong piston /rod combo. Al
 
Hello John achmann,

You did not answer my question about oil between the two moving surfaces? If the piston pin pushed right in and it seized, must have gone dry. You said the assembly was correct. Hard to believe that ALL the failure is in the same area. You need to take five and see what has accurred. Just approach it has if someone else has done it, and You are troubleshooting. I am saying take a different approach to your diagnosis, as of now you are thinking saying that you did everything right,
Guido.
 
better be checking clearances,... as they quite possibly could be a factory screw up. and that is why the piston maker is shutting you down. need more info like where were these made and who makes them? its all in the clearances.
 
Sorry I can?t answer the question of oil between the mating parts for I have taken this apart a little over a month ago. I?ve wiped all the parts clean to inspect damage and can?t remember what it all looked like. So tonight starting over fresh. I did noticed that the damage in the pin bore has occurred only on the front side of the piston.
 
What did the rod bearings look like? If it is an alignment issue, as possibly indicated by the pin being damaged on one end only, the bearings might show scuffing on just one side also. Could also be that the pin bore was not machined square to the piston body.
 
Does an old piston still exist to compare to the new ones, to check for any differences in oil drillings/passages between the old and new?

IIRC, some pistons direct oil from holes beneath the oil ring and/or the inside "dome" of the piston to holes that lube the piston pin bores. Look for any differences in things like that.
 
If all the wear is on the same side of each piston to me that sounds like an alignment issue. Either poorly machined parts or every piston or rod was installed 180 degrees off. The latter is easily done BTDT, did you notice when you installed the pistons and rods if they slide down easily and squarely on the journals or was there a slight drag? I do know that kits for some of the D series engine are cheaply universal. By this I mean that I believe the same solid non oil galley cam bearings possibly others are supplied for both the B and C kits and the smaller D series kits which is correct for the B's and C's however for the D's you have to remember to drill an oil hole in them prior to install. As already stated clear your mind and approach from a differant angle. HTH
 
Try clamping a piston pin in a rod without the piston then check the pin for round with a micrometer. Possibly distorting the pins when clamped could cause them to stick . It's a bad feeling when a fresh engine goes down. Let us know what you find.
 
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