i hope you guys can help.im in the process of buildng up a slightly uprated engine(approx 420bhp).i recently got some second hand mahle pistons that have hardly done any miles(under 1000)but the rings have been taken off and ive no instructions.i know how the oil rings go and which rings go where(by how they sit in piston) but wondered what way up the rings go?? is the small circular mark on the secondary ring on top(facing heads)or on bottom(facing crank)??? the rings have a shamfer on inside,do they face top or bottom?? standard piston had shamfer on top of ring!? (this is the same question really)

also the have put rings into bore to check ring gap and the top rings are approx 0.020" where the secondarys are approx 0.012" they dont appear to have been gapped/filed down before but thought they should be top 0.009 and 2nd 0.012. what would this do to engine/performance??

any help with this is much appreciated
pete.

 

Top rings are usually, if not marked by a dot, & are bevelled on the inside, the bevel or chamfer faces to the top of the piston.
2nd rings with a dot faces to the top, if no dot & is bevelled or chamfer on the inside it faces down, from the piston top.

Ring gaps are 0.0045" - 0.005" per inch of bore dia for top rings, so your 0.020" is about right.
2nd rings are 0.0055" - 0.006" per inch of bore dia, so your rings require enlarging, this figures are for std type builds, larger gaps may be required in certain other running configurations.

 

thank you for your fast reply,can anyone back this info up? heard few different gaps so far!! bore is standard 92mm
thanks
pete.

 

If you don't trust what i have quoted, i have been building engines for 35 years, 20 off which were building F1 engines for Ilmor & Mercedes, & currently build Subaru engines for several front running race cars.

 

Tbho I would be putting a new set of rings on even with low mileage due the low cost for peace of mind mate.
Then you can be confident gaping with fresh one's.

 

Motors S is spot on. I have your question on my web page, but I opened this one first!
Do what the man says.

 

thanks for your advise guys,didnt mean it to sound like i doubted you at all(motors s) but so much differing info on internet that i wanted to get a few peoples opinion because it seems different people do it different ways.info was spot on so thank you for your help with this.i would not have doubted you for a second if i had known of your experience etc.ive been working on car for years but not subaru uprated engines before and needed some good advise,seems that sn is spot on.thank you again.
pete