Hello,
What piston rings to the cylinder wall gap/clearance do you have when you built your motor with forged pistons?

0.50?
0.40?
0.30?
etc etc

I am trying to built my EVO 9 motor and I need to know this information.
Will a big gap like 0.40 leave oil pass through the ring to the chamber?
Does you motor burn any amount of oil?

Which ring is for oil control top or the second ring?
Cause Total Seal told me that " top ring gap has nothing to do with oil control. It is the 2nd ring and oil rings job to control oil. Top ring is a compression seal."

 

Just to correct your question, those measurements should be 0.0xx"

 

I think that the numbers Cosworth and Total Seal said to me are on mm

 

Are you asking about piston to cylinder wall clearance or ring end gap clearance? Two totally different things.

Piston to wall is set by the machine shop that is boring/honing the block and the piston manufacturers recommended clearance.

Your piston rings may be a "file to fit" set in which case you need to follow the manufacturers suggestions (or a trustworthy engine shop) and using a ring grinder you would need to set the compression ring (top) and the 2nd ring gaps by fitting them squarely into the bore and measuring the gap w/a feeler gauge.

A time consuming but extremely important part of setting up an engine.

Paul

 

I am asking about the piston ring end gap.
Does anyone knows about the gap of his built engine?
Hope some vendors/engine builders answer us.

 

I can't recall exactly but my engine had somewhere in the 0.016"-0.019" gap

 

Does your engine burning oil or not?
I think that is .40 to .48 cosworth/TotalSeal numbers.

 

Common units would be good in this thread, I beleive you are talking metric/SI units where the rest here are thinking imperial.

0.3mm = 0.0118"
0.4mm = 0.0157"
0.5mm = 0.0197"

Different builders have different opinions on what is a good ring gap. Two things are for sure.
1. You want a little more gap on the second ring then the top ring to prevent ring flutter.
2. You want to make sure you run enough end gap to prevent the ends from touching under high temps. The gap closes and lots of bad things happen.

 

no problem whatsoever.

 

Any pro EVO engine builders ref?

 

I have built many 4g63 engines over the years with forged pistons. You have to remember the piston ring expands quite a bit. The gap gets much smaller when the ring is at operating temp. You also have to keep in mind that the ring seal is accomplished by pressure behind the ring that pushes it up against the cylinder wall. The pressure comes from cylinder compression that passes through the gap to behind the ring. Running tight gaps is asking for trouble. There will not be enough gap left to sufficiently pressurize the backside of ring. This is what leads to ring blow by. Most people who run tight gaps have ring seal problems. Loose gaps make for good ring seal. I recommend top ring at .020-.024 and second ring at .024-.028. I have run .028 top/.030 sec with good results. I have seen blow by issues with gaps of .016 and under. Hope that helps.

 

Does anyone else has different opinion???

 

Who's pistons and rings are you using? What material is the top/second rings?

The top ring end gap is generally around .020" (.50mm), but may be different depending on your application. The second ring is generally a little larger. What are you doing with this engine? Drag only? Road race? How much boost? Since your ring end gap is directly related to heat, this informaton helps decide what will work best.

 

Cosworth Information and reference said the opposite.
Top Piston Ring gap 0.40-0.46
Sec Piston Ring gap 0.36-0.41
Oil Piston Ring gap 0.20-0.70

Bad things like....

 

I use cosworth piston and rings.
The gap that leaves the second as I told before is 0.36-0.41.
The gap of the secong ring is smaller that the top ring end gap 0.40-0.46

My mechanic told me that we have to fit a new top ring to make the top's ring end gap 0.30mm-0.35mm