Piston Ring End Gap

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69Chrgr

Charger/Cuda
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What kind of piston ring end gap should I have? I'm building a 360/408 stroker with Indy 4.00" crank, and protru pistons at .030 over. I'm using my old pistons to square the rings up for accuracy, and the rings all seem to be between .018 and .019 on the first and second piston rings. Is this correct?
 
The paperwork with the rings should tell you what gap to run depending on the useage of the motor.


Chuck
 
Just to add if the are single moly's these days the 2nd ring is about as large or large than the top ring. NOS go looser.

In most cases about .004 per inch of bore, so most likely about .016-.018 on top, and .018-.020 on the 2nd. But as 340Mopar said check with the ring company.

good luck!
 
You are better off using the piston manufacturers recommendation for end gap. Piston design considerations (like Keith Black pistons) require more end gap because the ring is closer to the top of the piston.
 
The ring manufacturer paperwork has gap dimensions per bore diameter inch lists for cast, forged and hypereutectic type pistons. Also the paperwork will have different dimensions listed for blower/turbo applications, drag race, circle track and street. Well at least Sealed Power rings have this info included with the rings. I assume or hope the others would also.


Chuck
 
Unfortunately, these rings say minimum end gap .004. That is it! I called Indy where I bought them from this morning, and they said that they gap their rings between .025 and .032. They also said it was completely up to the engine builder. So what do y'all think?
 
My machinist has me run my forged pistons at .017 to .019 which is basicly in the range of stock and they work fine,as said already hypereutectics require more gap.To be really confident ask your machinist.
 
69Chrgr said:
Unfortunately, these rings say minimum end gap .004. That is it! I called Indy where I bought them from this morning, and they said that they gap their rings between .025 and .032. They also said it was completely up to the engine builder. So what do y'all think?
Click to expand...


I think they mean .004 per inch of bore? I would go in the low .020.-.024 range and you should be OK, but can you call the manufacture and talk to a tech to be sure?

PS better to loose than to tight... on rings :goodman:
 
Thneold standard is .004 per inch of bore. I always rounded up. So on a 4.03 bore that would be .017 on the top ring. One of the newer ideas is to run a wider gap ont eh 2nd ring. It makes sense if you know what the rings do, and how they do it. In this case, I would run a .020 gap on the 2nd ring. That general guide works for forged and cast pistons. It DOES NOT HOLD TRUE FOR HYPEREUTECTICS or many gapless rings. The best bet is to look what the piston manufacturer says to run, and the ring manufacturer says to run, and take the largest gap between those two. That means on some hypers, a top ring gap of .030 or more is right depending on usage. You always want to plan for worst case. And slightly big will only give up some power, not break anything. too tight will break something.
 
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