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Engine ring gap

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70herald

Luke Skywalker
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Hi
Glad I asked about the engine rings. Took two sets off of their pistons tonight, and both of them were way to tight no gap at all on the top compression ring.
Interestingly, both 2nd comp rings were perfectly sized with 0.008" gaps, so they clearly know how to cut them to size. Kind of tough getting the rings off of the piston. Maybe next project I will plan ahead /ubbthreads/images/graemlins/crazyeyes.gif
Yisrael
 
Good thing you checked, eh? I suspect that you might have had to pull them out anyway, possibly after having broken a ring (or worse). Whew!

Those second rings sound near-perfect, following the old rule-of-thumb of approx. .003" gap per inch of bore.

You are using a ring expander (or at least a pair of feeler gauges or similar) to R&R the rings, right?
 
I very carefully took them off by hand. While I am a somewhat compulsive buyer of tools, a ring expander is not one of the tools I own. (and at 10:30 at night, there are not alot of place to borow one.)I do have a ring compressor.

I am using Deves rings. Actually it makes sense that the top ring needs to be adjusted per engine. The 2nd ring really is a glorified oil scraper and does very little in terms of holding in compression. On the other hand a very accurately adjusted top ring is good for maximizing efficiency.
Happily, I have now gotten all 4 sets of rings off, adjusted and back onto the piston without breaking them, bending them.... or some other damage.

Considering how tight they were, I think that you are right Andy, they probably would have broken very quickly.

Yisrael /ubbthreads/images/graemlins/smile.gif
 
[ QUOTE ]
...The 2nd ring really is a glorified oil scraper and does very little in terms of holding in compression. On the other hand a very accurately adjusted top ring is good for maximizing efficiency....

[/ QUOTE ]True enough! Case in point: I have a '64 Spitfire that at one time was an SCCA G-production class race car. Near as I can tell, the car was built in the latter part of the 1960s (very much to Kastner's comp. prep. manual, I might add). A friend and I acquired it in the early 1980s after it had been abandoned for a number of years. Luckily, no engine work was needed at the time, and we ran it for a number of years as an autocross car.

Anyway, by the mid-1990s, it still ran strong but was blowing oil smoke everywhere. Time for an overhaul. I was not surprised, upon removing the pistons, to find that at least two of the pistons' top rings were broken in several places. What DID surprise me was that none of the pistons had 2nd compression rings! /ubbthreads/images/graemlins/shocked.gif I was told at the time by a number of folks who should know that this was a classic "trick" used by many race engine builders.

Fine, but I wasn't that interested in risking things again. Pistons were ok and bores only needed a quick ridge ream and hone, and I then went with a set of Grant cast iron rings with 2nd rings converted to "gapless" by TotalSeal. Those worked out great, and the little autocrosser was soon strong as ever! /ubbthreads/images/graemlins/driving.gif
 
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