piston ring gap

[robin rose]

Hi Guys, can someone tell me what the correct gap is for piston rings ref iron barrel VH with Heplex piston 10793.
cheers. Rob

[brenton.roy]

Hi Rob, Nicholson suggests 15 thou"
Brenton

[nevhunter]

.0035 thou per inch . same answer as Brentons but works for all sozes.. If you want to finess it consider the finish on the outer face of the ring . Sometimes it is deliberately rough for quick bedding in, and you might be game to try a bit less. Unless your bore is true check carefully in the smallest place, but you can ignore the unworn bit at the bottom and extreme top as the ring doesn't run there. Nev

[david.anderson]

While some ring manufacturers specify .0035 per inch of bore I also have ring sets that specify .002 per inch of bore. It should also be noted that the Ariel Owners Guides for the singles 1950 (page 17) and 1957 (page 19), (the 2 owners guides I checked, and probably most other) states “When fitting new rings, the gap between the ends of the ring, when tried in the cylinder should be from .006in to .008in. It is possible for the gap to increase up to .025 - .030in before replacement.”
I have always gapped my VH rings to .006” - .008" (at the bottom of the bore on other than a new bore) and have never had a problem.
David

[nevhunter]

I guess it depends on how you treat it when it has little miles on it. IF the end gap is not enough it will break the ring into small pieces. If you are in a dust free environment it takes a long time to wear much metal off things like pistons if the clearance is a bit lacking. In my younger days I tried to have everything on the minimum to make it quiet, and sometimes the bike would be tightening up when you are overtaking for what seemed years. I reckon people give them more stick these days than when they were new. Nev

[john.nash]

OriginalWellworthy packet in the garage says .004" per inch of bore (for aircooled engines)..... it seem we are all pretty much in agreement ..

[brenton.roy]

Sort of - there's a fair difference between 6 and 15 thou?
I know David has written that he runs in very carefully. Nicholson is also a reliable text - maybe the US riders ran them in a bit harder.
Waller doesn't give a clearance for singles, but does for everything else (strange?) - and gives 8 to 10 thou for 500 twins (63mm bore).
My (JP) VH rings were pre fitted to around 12 thou. JP organised the bore settings around their piston / rings.
So.. Maybe there's a minimum and maximum in there somewhere, depending on how you want to run the motor in?

[Paul Slootheer]

...and for running in I suggest to take your time. With modern lubricants it will take quite more time for bedding in compared to ''the older oils''...

Regards, Paul

[robin rose]

Thanks for the info everyone, think I might go for 10 thou!

[satchison]

Hi Robin,
Did .010" work well for your ring gap? Just getting ready to do mine (1947 350 OHC).
Cheers