We took apart a buddies head a week ago to have it sent out to get some work done to it, and while it was off we found a noticable gap in between the piston and wall. By the way its a LS block, standard bore, 8.5:1 pistons and GE sleeves. We ran a compression test a week before the head came off and numbers came up
180,160,180,180 i think or somewhere very close to that. the cylinder with 160 is the one with the gap to. Any opinions if the gap is to large, or if its normal.. or any opinions at all would help. thank you.

This pic is a bit blurry, but the gap is towards the bottom of the piston


this one is a bit more clear


dirty pistons, any clue on how to clean these while there still in the block?


Thank you.

 

Piston to cylinder wall clearance is measured between the piston skirt and the cylinder wall, not the top of the piston. The skirt area below the rings is lubricated but the top area above the rings is not, so you would never want the dry, dirty top area to rub against the cylinder wall. I'm not sure how big the top gap normally is but it's probably something on the order of 15-20 thousandths IIRC. DO NOT try to clean the pistons without taking them out as it only makes things worse. Anyway, those look fine to me.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tjbizzo &raquo;</TD></TR><TR><TD CLASS="quote">Piston to cylinder wall clearance is measured between the piston skirt and the cylinder wall, not the top of the piston. The skirt area below the rings is lubricated but the top area above the rings is not, so you would never want the dry, dirty top area to rub against the cylinder wall. I'm not sure how big the top gap normally is but it's probably something on the order of 15-20 thousandths IIRC. DO NOT try to clean the pistons without taking them out as it only makes things worse. Anyway, those look fine to me. </TD></TR></TABLE>

Learn something new everyday. Thankyou.

 

You really have to measure the piston to cylinder wall gap. Typical piston to cylinder wall gap is 0.003" for JE, CP, etc. Endyn/Wiseco run tighter gap around 0.0021-0.0022". The gap is measured from the piston skirt, approximately 0.5" below the wrist pin area. Its virtually impossible to eye any differences in 0.001", so its something that needs to be measured with machinest quality tools.