Ring end gaps; importance?

[Let'sgoflying!]

Superior has two significantly different documents showing ring end gaps on their website for the IO520. One is obviously older, one a newer SL, but I am wondering why they would continue to list the older one at all.

I talked to the tech rep and he simply said use the newer one.
Good thing I happened upon the newer one first before using the older one - or is ring end gap not so critical?
I think it likely someone will stumble upon the older document and use it, might there be any consequences?
Of course it is entirely possible I am misreading the documents and there is no disagreement!

A. This is "Piston Ring Sets, Ring Applications and Recommended End Gaps and Side Clearance for Continental Engines"
http://www.superior-air-parts.com/RIO/Cont/Reference/Cont_PistonRing_Clearances.pdf
SA5003 028-044
SA5004 023-039
SA5208 030-046
SA5209 033-049

B. click on "Service Letter L05-09 B"
http://www.superiorairparts.com/serviceLetters.asp
SA5003 028-044
SA5004 034-050
SA5208 020-036
SA5209 015-031

 

[n20junkie]

Ring gap is heat dependant.

You want the smallest gap without having the ring expand so much that the ring ends butt. Once that happens piston crowns are removed by the stuck ring.


Its pretty critical. The higher performance the engine, the larger the cold ring gaps.

 

[TripleZ]

Ring gap is heat dependant.

You want the smallest gap without having the ring expand so much that the ring ends butt. Once that happens piston crowns are removed by the stuck ring.


Its pretty critical. The higher performance the engine, the larger the cold ring gaps.

+1

In addition, a larger gap will allow more blow-by and sometimes oil consumption. (although those two are typically inverse). Too large of a gap, and you can gutter the top land from combustion gases racing past the rings.

You'll want the ring gap matched for the piston revision (land and ring groove geometry), the duty cycle, and bore. Hence why sometimes you do cut-to-fit rings.

 

[Tom-D]

+1

In addition, a larger gap will allow more blow-by and sometimes oil consumption. (although those two are typically inverse). Too large of a gap, and you can gutter the top land from combustion gases racing past the rings.

You'll want the ring gap matched for the piston revision (land and ring groove geometry), the duty cycle, and bore. Hence why sometimes you do cut-to-fit rings.

When you stop to think how much time 1 power stroke takes and how much gas can pass that gap in that time span, you'll realize that that amount of gas means nothing to compression or blow by.

the ever increasing gap during normal wear means the ring is loosing the tension it requires to do its job.

 

[TripleZ]

When you stop to think how much time 1 power stroke takes and how much gas can pass that gap in that time span, you'll realize that that amount of gas means nothing to compression or blow by.

the ever increasing gap during normal wear means the ring is loosing the tension it requires to do its job.

Compression, no. Blow by, yes. Although the mechanism is not combustion gases going through the gaps alone, rather causing ring flutter, which unseats the rings from the bore and allows blow by.

You can sometimes force or alleviate ring flutter by adjusting ring end gaps. Often closing the top, and opening the 2nd land will help.

Blow by can help excessive oil consumption, since your blowing oil back towards the crankcase. This you need to balance with breather carry over, so one consumption method is not traded for another.