Originally posted by fraz
Gav and rjl,
On the o-rings. You say 2.6mm and 1.8mm "section". I take it that is the thickness of the o-ring, right? Now what ID are each of them and for which size motor?
Yes, by "section" I mean thickness.
The part numbers for the ones I buy are:
What I did was to take a crankcase and a header down to the local bearing supply and try a few on for size. These are for a Nova .12 engine and the ID isn't absolutely critical. I'm guessing the ID is probably 1 - 2mm smaller than the exhaust outlet, but they stretch over the wider section without a problem.The main issue is to ensure that the two smaller section ones are a snug fit when you install the header.
The larger one is essentially a second seal and something to take the compression forces exerted by the spring. It ends up fitting nicely into the radiused opening of the header, but it's too large to go inside the header when mounted.
Also, the newer Nova engines have a machined surface on the exhaust outlet but older ones are left as cast and exhibit a little flashing. I just file this flashing off and blend the surface in to avoid a possible leak.