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Question for the experts re: piston skirt wear


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Hey guys and gals,

 

Had the original motor from my wagon sitting a while, decided to finally take a look. Ran well, burned 1-2 quarts, and was pulled immediately after head gasket blew and set aside. Cleaned up pistons a while back, and noticed some scoring in the #2 cylinder, top side. Finally popped the piston, and attached photo shows what I found. Wear on that side of the piston, otherwise in good shape. Wrist pin looks good, seated proper in the piston and rod. Rod bearing is good.

 

Curious if anyone's come across this kind of wear before, or if anyone wants to theorize as to what's behind this. This motor always sounded rather slappy on cold mornings, but I've never seen this kind of wear on the few other Subaru motor's I've had apart.

 

I was about to sell the short block, but I'm on the wall now. It's a cheap high mile motor that burns oil, but this seems abnormal. Guess I can just make it known to buyer....

IMG_20200815_130519.thumb.jpg.7e4e86f0dfdad9c3b6caf97b84581f1c.jpg

IMG_20200815_130408.thumb.jpg.1fb68e59b44b74526f55708870d9c8e5.jpg

Edited by awfulwaffle
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We do have a bore gauge set in the shop, going to take a look when I'm in the there next. Good thought. The scoring is very light so hopefully doesn't obscure the measurement.

 

Talked to a friend who has a lot of experience diagnosing 2 stroke engine failures and he says this looks just like soft seize due to overheat. That said, this is the intake side of the piston which seems strange - if it expanded non-uniformly I'd expect it to be on the exhaust side. That, and there's no abnormal discoloration and all 4 pistons look uniform.

 

I'll report back with measurements. Really curious about this.

Edited by awfulwaffle
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I assume this is on the power side of the piston?

 

Did some thinking on this. If I'm picturing this correctly, w/ CW crank rotation the #2 cylinder should clock slightly towards the intake side? Not sure if the wrist pin bore in the piston is offset to account for this, though. Also not sure if I've flipped things around in my head :lol:

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Did some thinking on this. If I'm picturing this correctly, w/ CW crank rotation the #2 cylinder should clock slightly towards the intake side? Not sure if the wrist pin bore in the piston is offset to account for this, though. Also not sure if I've flipped things around in my head :lol:

 

Power side of cylinder 2 would be the exhaust side of the cylinder bore. Is there any wear on the other side of the piston?

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Thanks Max, interesting that that's #2 in your picture as well. Remind me - that motor came out because it was an oil burner right?

 

I've seen the wear on the walls before, but not that bad on the piston itself in the few sets I've pulled out. Maybe it is just a thing that happens, though. I've got a 190k EJ255 sitting on the stand right now out of the wife's car, I'll take a look at that when I get bored (pun intended?).

Edited by awfulwaffle
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Minimal.

 

For my education - how's 'power side' defined in this context? Not really a positive displacement guy.

 

I took it to be the 'counterpressure side' described in the doc I linked.

 

Side that the rod is pointing to on the downward power stroke. That's what I was always taught :confused:

 

Surprised to see so much skirt wear and nothing at the top near the rings. Certainly would like to know more about how this happened. I'd be interested to know if that cylinder specifically was a larger bore than the other 3.

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