Ring gap,

G

GEOFFNZ

Senior Member
Advice please.What would be the suggested ring gap for cast rings in a 3 5/16 bore competition engine series 99.Do they need to be wider than in a stock engine to allow for a bit more heat. Thanks, Geoff.
 
rule of thumb for any engine is to have .003"-.004" gap per inch dia of bore.
Set your gaps .010"-.013" and you'll be fine.
 
If you read my book you will see why the second ring gap should be wider than the top ring.

The answer to your question will require more input from you----supercharged? Fuel type? dry block? type of competition?
 
https://www.hastingsmfg.com/ServiceTips/ring_gaps.htm

These are an examples of ring end gaps on a 7.3 ford diesel.
Notice the large gap on second ring.As JW states there are reasons for gap being what they are.The old blanket statement about .0035" per inch of bore doesn't stand in all applications. Or intended use.

Top - .014"-.024"
Second - .062"-.072"
Oil Ring - .012"-.024"

R
 
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One thing I discovered early in my engine building was the fact that the end gap grows very fast. When I built my first stockcar engine I set the gap at between .012/.015. It was near the end of the season and after we had run several races I was told by other builders that I should have set the gap at .020" this bothered me and when the season was over I took the engine home with me to freshen it up. When I checked ring end gap it was over .020" in most rings. I thought I'd used the wrong feeler gauge. However the reason was very simple. The old Grant rings were very soft and depending on the finish hone of the cylinders a little arithmetic says: .001" ring/cylinder ware = .00314" circumference increase. Thus those ring gaps get very large very quick. I don't suggest you reduce the size as not many people go racing any more, rings are better ans the honing process is a little smoother.
Next where do we put the gaps??
PS that's a great chart. Thanks
 
Thanks all,Reply to JWL re engine.Engine is used in mild vintage competition only in a 700kg special built about 1960.Does sealed circuit and sealed hillclimbs and doesn't run much over 4000 rpm allowing for it's age.Bore 3 5/16 stroke 4 1/8 running about 8.5 compression in "39 Mercury block with enlarged inlets and modified camshaft.Engine was built for that car in the 70s and has somehow survived considering how hard it was used by previous owners.Cheers, Geoff.
 
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