Mullet Z28

I'm running C&A Duramoly rings in a 383. The instructions suggest .0068" for every inch of bore in nitrous applications for a total top ring gap of .0274".

Right out of the box, the rings were already between .024" and .026". I found this very strange, but since I was shooting for .0274", I thought what the hey.

But now the second rings are WAY too big out of the box. C&A
recommends .0048" for every inch of bore, for a grand total of .0193. Before I even put the rings on a file, all of them have .028-.030" of gap already? WTF? This is a good .010 more than specified.

There are only two possible scenarios I can think of.

One, the rings are mispacked. Maybe these are for 4" bore instead of a 4.030" bore?

Two, maybe this Sears made-in-China feeler gauge is off?

Granted I'm not using a ring squaring tool, using the "upside-down" piston technique, I've been using great caution to make sure the rings sit squarely in the bore about 1" down.

I'd assume second rings that are .010 too big would mean a good deal of cylinder pressure loss and lots of oil consumption?

Advice? Suggestions?

rskrause

If the bores are right, and you are measuring right, the rings must be off. You probably know this, but you should be sure to measure the rings in the bore they are to be installed in. BTW: if the gap is too big, the ring is too small.

Couple of suggestions.

1. try another gauge.
2. measure your bores, are you sure of the diameter?

Rich Krause

Mullet Z28

Rich,

Thanks for the reply.

Yes, the bores are indeed .030" over. The 4.030" pistons fit in there snugly. The dial bore confirms that too.

But, upon some further research, it looks like C&A is one of those traditionalists that suggest a smaller 2nd ring gap than the top ring. Speed-Pro and others recommend a bigger 2nd ring gap. So, as the 2nd rings measure out of the box, I should be OK to leave them as is.

That way, I can appease both schools of thought by running the same gap on the top and second rings!

Damon

I'd call them to check if that's how they are supposed to be. Rarely do they recommend gaps you can't achieve with their own brand of rings.

Of course, if you are playing mix-n-match between piston and ring manufacturers all that goes out the window.

ALWAYS set gaps by the PISTON manufacturer's recommendations. Piston design and materials can GREATLY affect the ring gap necessary to seal it up without butting the ring ends under high thermal loads and instantly destroying the engine.

thewinner

are you sure you got the right rings for the bore size?

sleeperz28

I believe my speed pro's recommend .006 for every inch of bore on the top and like .005 for the second(on a blown app.) I had problems with oil blowing out the breathers with a 1% leak down motor. So I decide to gap both rings at .025 and call it a day. 1K miles down the road I have no more problems with oil out the breathers.
I believe nitrous motors gap the same, however I believe it depends on the shot you plan to run

Lonnie Pavtis

When you intend to file your rings, you must buy file fit rings. These are an additional .005 oversize on the top 2 rings to allow for filing. Usually the standard oversizes have a generous gap for all around use.

94bird

Yes, gapping the 2nd ring tighter than the top ring is an old school approach. There's no absolute gap that will work in all small block Chevys, etc. However, gapping the 2nd ring tighter than the top ring is just taking into account thermal growth and the fact that the top ring area will be hotter so the gap will close down more than the 2nd ring. Achieving close to 0 gap on both top and 2nd rings can be a recipe for disaster for ring dynamics in many applications. The typical starting point for gap ratios (2nd / top) is 1.5. We've discussed this before. If you do a search you should find it.

Mullet Z28

Yup, lots of good info in that thread, especially considered Chuck R. joined in.