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Re: Piston ring clearance in groove gap

I'd tend towards 2 rather than 4 thou. Ten thou is definitely too much. I think you've just found the cause of your pressurised crankcase.

Re: Piston ring clearance in groove gap

Various manuals give .005 as a reassembly limit for old pistons with new rings. .010 seems a huge space for a Seven with modern rings unless driven through a sandstorm or been fed Brasso to bed rings etc. Unless your car retains the original 5/32wide rings which often developed wide clearance, esp if stiff thick section rings been fitted.

The leakage path is the rectangle formed by the ring gap x land clearance. Vertical clearance alone has little effect. (Do not be tempted to fit really neat; the piston distorts under heat and load and the ring may jam. And gas has to reach behind the ring for it to function.) If the parts books 1029A is to be believed some pistons were drilled behind the 2nd ring rendering this useless for blow by control!

As a matter of interest I recently put new rings in a 1960s Brit car 170,000 miles. Top rings broken, 2nd about 3/32 gap. Distinct fumes from open crankcase as has been the case for 30 years but little effect on performance or oil use.

Location: Auckland, NZ

Re: Piston ring clearance in groove gap

Thanks guys. New pistons ordered.

Roly

Location: Upton upon Severn