> Hmmm. Okay, I have the manual, but I don't see how you did
> the calculation. I see crankpin diameter, bearing internal
> diameter, and bearing diametrical clearance, but not
> something that tells me the internal diameter of the rod
> (without the bearing in place). I seem to be missing
> something . . . ?
Page B1 (or page 85 of the Bentley), under "Big End", "Internal diameter of
bearing housing" is listed as 2.2327" to 2.2335".
"Bearing internal diameter" is 2.0882" to 2.0895". Subtract one from the
other and divide by two (as there are two thicknesses of bearing insert).
> I was trying to figure out what size
> bearing was used last time.
As a rule, undersize bearings have the undersize stamped on them. So if
they were .010" undersize, I would expect to find 010 on the back of the
bearing shell.
Guess I just assumed that, if you had the tools, you would have measured the
crank before turning it over to your machinist. But I don't suppose there
is any reason you have to, if you trust him to never make a mistake. Even
though the book says undersize bearings are available to .040" (and I think
.030" are, in fact, available), I don't like to go beyond .020" (based on
advice from people like Ken Gillanders and Greg Solow). So if a crank were
ground to .020" and worn enough to need it again, I'd go looking for another
one.
Also, to me, having the crank ground is something that is done only if
absolutely necessary. If it's within range and not too badly scored, I put
it back as-is. Since I've pulled apart a fair number of engines that have
clearly been worked on before, but have standard size cranks, I have to
believe that is fairly common.
Randall
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