head gasket question

[sangheraent]

well iv been running orings on all my motors and so Im not very familiar with the gaskets. Iv been runing an atc gasket but inside diameter is about 2-3 mm bigger then my bore. i have 68mm bore. am i losing compression from this gasket? i have stock gasket as well and its smaller then my bore so im afraid my piston is going to hit the gasket.

[Honda 250r 001]

are you sure your running an ATC gasket and not a big bore stock cylinder gasekt? sounds to me like your running a 72mm gasket for when people press big bore sleeves into stock cylinders. i believe ATC gaskets should be no more than 68mm

[sangheraent]

thats what i figured. I guess i may have the wrong gasket. how much compression could I lose because of that?

does someone make bore specific gaskets?

Assuming you have a squish clearance of .040” or 1 MM, you would have about 12% extra head volume. If your stock Honda head volume is 24CC’s, then you have approximately 2-2.5CC’s extra volume…a little more than what you want.

In the past, a few companies had “specific bore gaskets”, on my 330R and 363R, two O-Rings in each engine are used in place of gaskets and are specific to Pro-X & ESR cylinders, however; these are for 74MM & 78MM bores respectively...

Call around; check the Cometic site, someone mught have what you are looking for...

Carlos.