Topic: Using a head gasket that's slightly too large in the bore?

[drumstyx]

Getting a C65 (same engine as an S65) running, and currently just going to reuse the head gasket just to see it rev.

Of course, these are fairly rare compared to the C70 and C90, the former sharing just about everything except the bore diameter. Given that, finding the 63cc (44mm bore) head gasket is somewhat difficult/expensive. What IS very available is the C70 gasket, which is identical in every way except it's for a 47mm bore. This means that it'd have an additional 1.5mm clearance around the bore.

Now, obviously, if I *have* to replace the gasket with something, being a cheap build, I don't really care what it's for, but if being oversize would be just as bad as reusing an old correctly sized one, I won't bother.

What say you, gurus?

[Terry in Australia]

Don't worry about it mate, it'll be fine, a stock gasket for any bike is always a couple of mm bigger in ID, as long as the Fire ring is seated on the top of the iron sleeve and it can seal the mating surface on the head, it'll be fine.

[Sam Green Racing]

From a tuners prospective, not a good idea mate, this can cause a heat build up in the place you don't want one.
The top edge of the piston can be prone to damage the quickest.