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Broken / Missing piston skirt

Has anyone ever encountered a broken/missing piston skirt? See pic below which is of the #1 piston from my 83 3.0 engine. It does not look (to me) to be a fresh break. I dont really know but I tend to think it might have happened a long time ago. Surprisingly, the #1 cylinder had minimal scoring.

Where could the missing piece of have travelled? The size of the missing piece (assuming it remained intact) would be roughly 30mm by 7mm. With luck, it should have found its way to the screen above the oil sump plate, right? Possibly a previous owner could have found it there and removed it. But where else might I look?

The pistons were KS 9.3 CR mated to alusil cylinders. This engine has 127k miles and I am pretty sure it never had its heads off Currently the short block is on an engine stand in my garage. Besides typical wear, the other damage this engine endured was 8 broken dilavar head studs. Unfortunately, the engine continued to be run for some time, causing damage to cylinder to head contact surfaces. I already sourced replacement P&Cs (used) and rebuilt heads. Everything else has checked out OK Except now I have encountered this one more surprise.

Thanks,
George

Old 02-24-2021, 10:00 AM
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That's odd. The sump is about the only place a piece like that can go. Has the engine been apart before? Maybe a piston was dropped and the damaged and reinstalled anyway? The piece may have broken off at that time, or cracked and broke off while running. How does the top of the piston, and the rings, look? Or maybe a piece of debris got in between the piston skirt and the case while the engine was running and damaged the skirt. Any evidence of damage on the case near that part of the piston?

Last edited by stownsen914; 02-25-2021 at 03:54 AM..
Old 02-25-2021, 03:52 AM
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I can't say for sure but I found no evidence that the heads were ever removed. Tops of all pistons and all rings were 100% intact and looking good. And even the alusil cylinder bore that this broken piston was running in showed only a couple of very faint scratches but no gouges. The case structure behind this piston (and elsewhere) looks entirely fine. The only theory I have come up with is that the engine being run with multiple broken head studs caused some "twisting" in the cylinders that put pressure on the piston skirt and cause it to break. It is very sad to think of it, actually... But I am determined to get this engine fixed and back on the road. And as a next step I am going to take the sump cover off (again) and search thoroughly for the broken piece. If it broke inside the engine and fell out of the cylinder then it would have to be in the sump, right? And the screen being installed above the sump plate would have kept it from traveling elsewhere? thanks, George
Old 02-25-2021, 06:08 AM
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It would have to be in the sump somewhere, unless removed previously. Nowhere else for it to go, really.
Old 02-25-2021, 07:00 AM
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You could use a borescope to probe around and look for it.
Old 02-25-2021, 07:10 AM
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Take the borescope advice. Plenty of places for a small (but not too small) piece to hide in the sump. Under/around the oil pump. In the passages that drain the chain boxes, which are the closest to #1. Missing elephant foot nuts can sit down there comfortably for years.

What is the function of the bit which broke off? Does it help stabilize the piston, reduce rocking? Is the wear pattern on that side of this piston replicated on all the other pistons? If so, the missing part maybe not a cause of that?

Agree with your suspicion that all those broken studs may well have led to this somehow. Could it have rocked enough that it hit the rod?

Odd for sure. But then, so is running with 8 broken studs.
Old 02-27-2021, 12:26 PM
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By looking at the wear pattern on the skirt, it looks like it was broken from the inside out. Opposite of what you'd see by the piston being dropped.

I'm sure there are other ways that that could happen, but one scenario is where the crank was turned with the cylinder off and the piston still attached to the rod. The piston could "catch" on the case and the weakest piece would be the skirt extension.

Anyone else have a hypothesis? And you're sure that the engine was never previously torn apart?
Old 02-27-2021, 02:25 PM
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Quote:
Originally Posted by dannobee View Post
By looking at the wear pattern on the skirt, it looks like it was broken from the inside out. Opposite of what you'd see by the piston being dropped.
Interesting observation. I'm trying to imagine how the skirt could flex outward though while it's in the cylinder, if it occurred in an assembled engine.
Old 02-27-2021, 04:25 PM
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It could have caught the edge of the case with the cylinder off. Broke when the crank was turned without paying attention.
Old 02-27-2021, 06:15 PM
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I've had a piston hit the case that way, but not with any force - just a momentary bother. But it is better than my guessing.
Old 02-27-2021, 10:55 PM
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I’m guessing it was built like that from the factory. Probably late on a Friday before a 3-day weekend, haha
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Old 03-01-2021, 04:01 PM
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Quote:
Originally Posted by gssereik View Post
I can't say for sure but I found no evidence that the heads were ever removed. Tops of all pistons and all rings were 100% intact and looking good. And even the alusil cylinder bore that this broken piston was running in showed only a couple of very faint scratches but no gouges. The case structure behind this piston (and elsewhere) looks entirely fine. The only theory I have come up with is that the engine being run with multiple broken head studs caused some "twisting" in the cylinders that put pressure on the piston skirt and cause it to break. It is very sad to think of it, actually... But I am determined to get this engine fixed and back on the road. And as a next step I am going to take the sump cover off (again) and search thoroughly for the broken piece. If it broke inside the engine and fell out of the cylinder then it would have to be in the sump, right? And the screen being installed above the sump plate would have kept it from traveling elsewhere? thanks, George
Can I assume that since the engine is stripped to the short block, and on your engine stand, that you are splitting the case and checking everything else? It's really not that much more work to get a real good look.. see if the pieces are wedged somewhere, or if they have done any other damage to parts of the case?
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Old 03-03-2021, 12:06 AM
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George - on rereading this, I see a misconception on your part. There is no screen between the crank/rod/cylinder upper part of the case, and the lower sump part. The 2.0s had a screen there, but not later engines. It actually is probably better to let stuff fall all the way down into the sump - fewer moving parts there to cause trouble. The oil pump intake, of course, has a screen, and only something very small can get through that - certainly not a chunk as large as this one was. Which is why it most likely is lodged in some nook or cranny in the sump where you can't see it (at least without a bore scope).
Old 03-04-2021, 03:42 PM
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Thank you for all for your advice! I appreciate it. I bought a Boroscope at harbor freight and will be taking a really good look inside the sump of my 3.0 engine case. I will report back afterwards. Hopefully I might find the broken piece. The engine is on an engine stand currently and is stripped down to the short block. So I have plenty of access points. I am considering splitting the case but really don’t think I will find any issues inside. So for now I’ll just try the boroscope and see how it goes. Thanks again.
Old 03-05-2021, 11:28 AM
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2.2's came with a screen also .
Old 03-06-2021, 06:50 AM
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So little effort to split the case now and I think for a few more good reasons:
the missing parts
the 'engine full of surprises' (who knows what else without splitting?)
IMS bearings always need a change anyway
Old 03-08-2021, 09:55 AM
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UPDATE: Last night I had a really good look inside my short block with the boroscope that I bought at harbor freight (Cen-Tech 2.4" LCD Inspection Camera). This camera worked very well and I poked it through each opening and maneuvered throughout the case. I am feeling very confident that the missing piston skirt must have found its way to the sump plate screen and was removed at some point. Everything looks very clean inside and since taking the heads and P&C's off I have been careful to keep debris from getting inside. I appreciate the advice that some have given that I might go ahead and split the case and I am giving this serious consideration. But at this point I am leaning towards keeping the case as-is and proceed with top-end re-assembly. The engine has 127k original miles and I am encouraged by what the boroscope showed me. Unfortunately, I need to stick to a tight budget for this build so I am installing rebuilt heads and a new clutch but otherwise I am going with used parts (original alusil P&C's, camshafts, lifters, etc) which are still in good shape and measure within spec. So my hope is to get maybe 50k miles or more with the expectation that I will need to pull the engine again at some point to tackle a full rebuild. Let me know if you feel strongly that I might reconsider and do the case split now. If I was doing all new/rebuilt components then I would definitely split the case. But that is not in the cards, so I will probably take the bet that there are no more surprises and that the short block has as at least as much life in it as some other major components. Thanks again, George

Old 03-09-2021, 08:45 AM
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