Motor was running fine till I blew a shift and bent some valves. This is a turbo motor that has been run about a 12 times over the last year and a half. After the head was off I noticed #2 and 3 cylinders looked rough so I pulled the pistons . My question is what will cause a piston to look this bad on one side and this good on the other. Any one have any ideas why ?
Both pictures are of the same piston

 

I don't have an answer for you, but i am curious as to what pistons those are?
sorry, that really sucks.

 

Thats ok well get it back together again, just hoping to avoid this next time. the pistons are from Arias

 

Slight bearing slippage perhaps??

 

which side is it scuffed on? the intake or exhaust? Check the cylinder for our-of-roundness. Is this the only piston that looks this way since you stated two cylinders were rough looking?

 

There are 2 pistons that look this way. And 2 bearings that where closing up and pounded more than the rest. The bearings are shinny with ware and are no longer able to snap into the rod bore. They fall in lose. Lock tabs are still there, nothing spun but 2 bearings are more closed than the others and have had more metal flak off than the other 2
After this closer look at everything I think I got it figured out. 12,500 RPM caused the bearing to begin to pound with the result of bearings starting to collapse and metal flaking off and being sprayed onto the cylinder wall. The thrust side of the piston... being on the wall was taking all the abuse from the particles in the oil.
would this seem reasonable ?

 

what you're saying makes sense. what do your cylinders look like?

 

I didn't tell you the whole story because I was trying to understand the piston I showed in the picture. scuffed on one side. The other one was scuffed on both sides. The wall of the piston with the single scuff mark was skuffed on the exhaust side. the other which was skuffed on both sided will likely need to be bored. But I was thinking that the piston with the single skuff would lead to the answer of why this happened because it's so unusual.

 

u ran lean?

 

When your cylinders start to look like () or ovalled, you'll start to have piston slap. This also causes your pistons to wear, but more likely you had contaminents in the chambers to cause such damage. Let's see your cylinders. Depending how much damage was done to the cylinders, you can bore safely to 81.5mm. 82mm is pushing it with stock cylinders.

 

This is a darton sleeve motor in a car that runs low 10s- 84.50 mm bore. the wall will clean at 85 which is where this thing is going next. Yes the skirts were collasped in the skuffed pistons but the tops of the pistons look fine except for the valve mark in the exhaust pockets.

 

Is the 2nd ring pinched or does it still move freely?

 

That was the first thing i checked when i saw the damage. All rings are free moving

 

if the machine work wasnt done right meaning that if the bore wasnt machined correctly that will happen . this happens alot to alumin block when it over heats or excessive heat

 

What error did the shop make that can cause it to scuff on only one side and one side only. That doesn't make sence to me
There are many things that can be done wrong to cause a piston to scuff on both sides but scuffing on only one side means the other side had clearance. thus it's not the bore size.

 

tell ya what go mesure the bore and see what it reads . i have a set of je piston like that . im not saying im right but ive had the same issue before.

 

I shattered the ringlands on one side of the piston and the other was perfect. I guess anything is possible.

 

If the cylinder was ovalled on one side and not the other, which would make sense in this case, for one piston has damage on only one side, and both for the other. Remember that cylinders are tapered, so clearances from top to bottom will be slightly different, but if it's uneven at any given point, can cause serious problems as such.

 

Looks like piston slap. That's what my piston looked like(only one). The "official" cause is over revving a "cold" engine? I didn't! I don't believe it but it was under warranty

 

After looking at your pics looks like it could be a bent connecting rod. I seen that cause uneven wear on one side of a piston before. also could be due to excessive piston to wall clearance as well.