> Scott Fisher notes:
> <If the rod bearing journals are supposed to have a clearance
> of 0.01" to 0.027", you do what Kaeding did to my crank and grind
> them all to 0.01" for maximum smoothness.>
>
> DON'T DO THIS! Actually, your machinist won't let you!
> Bearings run in the 1-2 thousandths (of an inch) range.
> Scott misplaced the decimal point and meant to say:
> ".... a clearance of 0.001" to 0.0027".
Boy, did I *ever*. This is worse than the time I told someone
that the valve clearance was supposed to be 0.21"... :-)
> On the other hand, I once had a 948cc Bugeye crank machined to have .003"
> bearing clearance, used straight 50W Castrol and the engine revved very
> freely.
That's another good point -- race motors often have larger clearances
for both cylinder bores and bearings than street motors. The object
is to give less friction and higher RPM operation, at the expense of
durability and oil consumption. There's a famous ad for the Lotus
Elite (the original, and still cham-peen, as you might say) that tried
to make its vast oil consumption out to be a virtue. The Coventry
Climax 1100cc that came with that one (I'd say it was the original
FWA, and hope that I remember letters better than numbers...) had been
designed as a fire pump motor and then modified to drive race cars,
both operations designed for full throttle operation when relatively
cold; for some reason I've never puzzled out, this led to wide bore
to piston clearances, which sucked up oil at an alarming rate. So
Chapman tried to sell this as a virtue...
I could find happiness with an early Elite, I suspect, as long as the
glass-fibre frame was still solidly bonded to non-rusted metal grommets.
But I would feel a little nervous every time I plopped my > 2cwt corpus
into the seats and heard the creak of resin against mounting hardware.
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