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Jan 22, 2011 - 2:02PM

M20 Piston rings

I have a piston M20 +30 thou, On the top groove which is normaly a dam groove & left free, this one has a ring in it. Now do you think that I should remove it? or should I just leave it & I suppose in theory it should give me a slightly higher compression rate.

Thanks for your input in advance.

TTJohn

email (option): Jomichael@aol.com

Ian Wright

Jan 22, 2011 - 3:20PM

Re: M20 Piston rings

Hi John..Occasionally a piston turns up with a ring fitted to this groove. The last one I had was a NOS aftermarket piston...and I guess yours is, as it is a +.030" size.
Any possible difference in compression ratio would be minuscule and, if present at all, not noticeable.
On the few occasions I have had pistons fitted with the 'fourth' ring I have run them like that without any problems.(or apparent benefits). I have just rebored an M20 barrel for a 'split skirt' type piston which runs at a much tighter piston to bore clearance...also not a very common type in my experience...Ian

email (option): julie@wright52.plus.com