G'day blokes,
I'm not entirely comfortable with Mr Grant and his new piston rings... Top ones have a gap of •018" while the second and oil rings are only •015“
For memory the rule of thumb was 10 thou per inch of bore diameter, so I should have around •035" or •040“ ring gap? The MTFCA manual covers original rings, specifying •003“ •005“ & •008“
I'll go do something else and rumenate on it I think.
Cheers
Anthony
Mr Grant's are spot on, .003-.005 per inch of diameter.
I agree with Kerry
.016 to .020" for the top. Better .018+
It is .005" per inch of bore.
second ring can be .015".
Grant Rings are my choice. I've installed two sets this month.
Your book was printed when the gasoline was not so hot. .008 will no doubt be trouble, except possibly for the oil rings.
For anyone else reading this posting "always" check the ring gaps in the bore, numerous times brand new Grants rings have come with a gap 0.028"++ which is way way to big.
An alternative is to purchase the next oversize up, and hand file the ends to achieve your 0.003 - 0.005" per inch of bore gapping.
It depends on how the cylinders are finished. If you're planing on a "break-in" and use a cross-hatch pattern, starting with a clearance of .005" per inch of bore will put you beyond the service limit pretty fast. The ring gap will increase .003" for every .001" of wear on the cylinder bore. That's only .0005" of wear on the cross-hatch pattern on the cylinder wall.
Ford used a rolling ball finish at the factory. This produced a near mirror finish on the cylinders as well as a near perfect bore.