qik1000 wrote:
Well, here's my two-bobs... I agree with a lot of whats been said already, and disagree in some instances. My experiences have been with a race prep A15 and as such only relate to that - not a street or stock motor!

We have broken quite a few head bolts - we were using NEW nissan bolts over tensioned to avoid blowing head gaskets. We've moved to new class 12.9 cap screws for all head bolts except the unusual bolt for the oil flow. For this one we use a new nissan bolt but don't use it for any more than two head bolting applications.

We've broken one crankshaft. We got four years of racing out of that one and expect to replace cranks now every two years.

We've always used old rod bolts with standard tension and (touchwood) haven't yet had a failure. But I feel we've been very lucky although we don't use them more than two applications in race use or two years.

We've also never thrown a flywheel. Other people we race with have thrown them on more than one occation. We over tighten them as well and use new class 12.9 cap screws. Same on the clutch, but I think thats overkill.

the main pulley seems to be cracked every time we pull a motor apart. The key that drives it actually widens the keyway in the crank and causes a local increase in diameter in that region which cracks the pulley through a corner of the keyway. None have come off completely but they don't last long. I'm going to make a new one from a tougher material than the original cast iron.

Hope my experieces can help in someway!

Daniel.

EDIT: Oh yeah, pistons don't have a real long life either in our engines. But they have traditionally been machined down mazda pistons. I'm currently trialing a different idea at the moment!