Piston issues - what would cause this?

[mr.radon]

My guess is a really hot engine getting stopped, cools off and then started again? Anyone else seen this?

Also, most of my pistons have scratches down the sides below the rings, what causes this, is it bad?

Can you just replace a single piston or should I get a whole new set?

Anyone have input on running forged (turbo) pistons in a non-turbo car?

Anyone tell me how to replace the pin bearing on the upper part of the connecting rod?

 

Links to the bad piston pictures:

http://www.ultimatesubaru.org/forum/attachment.php?attachmentid=2034&stc=1&thumb=1

http://www.ultimatesubaru.org/forum/attachment.php?attachmentid=2035&stc=1&thumb=1

[erik litchy]

were the cylinder bores damaged at all?

[calebz]

Anyone have input on running forged (turbo) pistons in a non-turbo car?

Running Turbo pistons in a nonturbo car would only result in a drop in power due to the subsequent lower compression.

[rallyruss]

I think you guess as to the cause may be close. overheated old motor. piston got really hot expanded and scrubbed the walls of the cyl.

 

dont think its an oil issue really.

 

oh and if you have a set of forged pistons for an EA82 turbo. sell em those are like gold. stock turbos ran cast pistons.

the real difference is the compression. you would turn the car into a slug.

[Mudboat]

I pulled out a piston a few months ago after I ran a compression check and found 40 psi. The piston looked almost just like that except that a compression ring was also broken and seized in the groove. The oil ring was seized in the groove about 3/4 of the diameter.

 

The cylinder was not scarred, but did have some mild scratching. I ordered a single piston and rings from Car Quest, ran a hone in the cylinder, installed the new piston and it came back to life with no problems.

 

A mechanic that looked at the old piston told me that the engine looked like it was overheated and was running on oil that was broken down. Note: It was like that when I bought it.

[mr.radon]

There was a small amount of Al smeared onto the #2 cylinder wall. Other then that (it came off with my finger nail) the walls were perfect. You can still see the honing.

 

Piston - forged (turbo)

I thought the pistons were all the same size and the crank was different for the turbos? So if I go for the forged pistons my compression ratio will change?

[naru]

My guess is a really hot engine getting stopped, cools off and then started again? Anyone else seen this?

 

Overheated piston expanded until there was no clearance in the bore.Probably oil related.Last one I saw like that was from an engine driven hard over a mountain pass while low on oil.I`m guessing this piston came from a cylinder whose rod bearing is near the end of the oil supply "line."(a rear one?)

 

Also, most of my pistons have scratches down the sides below the rings, what causes this, is it bad?

 

Hard grit caught between the piston and cylinder.

It ain`t great,but minor scratches are tolerable.

 

Anyone tell me how to replace the pin bearing on the upper part of the connecting rod?

 

This is a machince shop job.

[Petersubaru]

I would flawlessly clean the pistons up and install new rings from Nippon Piston Ring .. they will give you the tightest ring gap possible, providing your clyinders are in good shape...the scatching on the side of the piston is caused from Pinging (the piston vibrates inside of the cylinder when this happens) and the large blotchy marks seem to indicate at one time a blown head gasket slowly leaking without any one takeing care of it...check inside the cyl and make sure that the walls don't look like this...turbo pistons produce less compression and I believe (not sure ) that the piston wrist pins have more slop in them for heat related reasons