The Steamboating Forum

How much clearance should i have between the Piston ring groove and ring

I take it you do mean between the side of the ring and the side of the groove?

About a thou, to a thou and a half, (0.001" - 0.0015"), not a lot! It's not as vital in a steam engine as an infernal combustion engine, but small is good.

Thanks, should i cut two grooves? one for each ring, or two rings in one groove?

johnp wrote:Thanks, should i cut two grooves? one for each ring, or two rings in one groove?

I used two separate grooves on Otter's engine, which seems to work just fine. Make sure to check end gap on the rings by sliding the rings down (square w/) the bore using the piston.... if it's too tight, things may break. You want about .004" per inch of bore diameter end gap going by gas engine practice; I used Maytag engine rights in Otter's engine as they were readily available and the right diameter; since I made a new piston any height would work.

- Bart

John, it is not unknown for two rings to use one groove, but if you have room for two then go for it. It is also best practice to stagger the ring gaps to opposite sides of the piston when fitting to the bore, they will not turn in service.

I would also perhaps suggest that 0.004" per inch ring gap is a little on the large size for steam. It is all to do with expansion, and therefore temperature. Steam engines don't get anywhere near as hot as internal combustion, so less will still be adequate. Compressors run with only 0.001" per inch Dia. but then they don't get as hot as steam engines. I would say around 0.002 -0.0025" per inch Dia. will be fine. The ring ends can be dressed carefully with a file whilst held gently in a protected vice.