Piston Ring Gap - Specs?
 

Anyone know the spec for new ring gaps and whats acceptable for the 993 engines. JE 100mm pistons with Geotze rings. I have heard the later engines had tighter ring gaps. The cylinders were replated and honed. Thanks.

Bump ... inquiring minds want to know, lol. Doing final checks before sealing up.

Thank you Steve W.

"993 ring gaps are all basically the same; new rings are .008-.016 for the compression rings & .012-.024 for the oil rings. Its a wide spec due to manufacturing tolerances and cylinder bore condition. Max gap is .031 & .078 (which is pretty bad)."

Careful, I have found that minimum ring gap for the typical top ring from J.E. needs to be at least .014 for 100mm bore.

If you are running O.E., then you can run the O.E. specs.

I remember there being a chart on a ring manufacturers web site.
It stated the gap needed for the size of the bore.
As the bore got bigger...so did the gap.
So...Aaron is probably correct....008 may be OK for 92mm bore...but a larger gap is needed for the larger 100mm barrels.
Bob

I think all of the charts are for cast iron bores. Gaps can be tighter on aluminum cylinders, because of cylinder expansion when at temp.


I use PI (3.1415) x bore dia. to gap the rings from J.E. in aluminum cylinders for street use. I have run this gap in mild competition engines with success.

For safety,you can use 3.5 to 4 x bore dia. in competition engines. It prevents ring gaps from closing if the engine may see higher than expected temperature.

Sorry, Aaron -- can you clarify the "pi x bore dia" as it relates to ring gap. That gives 314 for a 100mm bore, and I can't correlate that to anything. Maybe I'm just dense ...

Brian

This is what I got for ring gaps for the compression rings. I havent done the oil rings yet.

http://forums.pelicanparts.com/uploa...1415410907.jpg

Sorry, 3.14 is for inches. 100mm would be 3.937"

So 3.937 x 3.14 would get you 12.36 or .012" or ring gap

I gap the second ring larger than the first to prevent ring flutter. Other than that you are looking great.

Thanks Aaron. I need remeasure a few when I do the oil control rings. They seem to be in the upper end of the new ring gap spec that Steve gave me. Are you saying that the min gap should be .012" with your calculation?

Yes, minimum would be .012

Your top ring gaps are great. Just make sure your 2nd ring gap is a couple of thou larger than the top

Thanks. I appreciate the info from you guys. Love this forum!

Just did this in my 95mm motor... All the rings where very tight to start...

1st .0167"
2nd .0187"
Oil .015"