Bob Jones writes that he has 2 in a diamond on each of his pistons, which
must denote a .020 oversize. I don't think so. The mechanic who rebuilt
my Bugeye engine showed me similar markings and explained them. At the
time, I was not particularly interested, so may remember it wrong. But I
think he said that nominally standard pistons on the assembly line were
graded by precise size, and marked. Then as blocks came along, the final
bore was measured, and appropriate pistons were chosen for best fit. If I
remember that correctly, then the number in the diamond does not signify
.020 oversize, but rather a slight variation on standard. I'm posting
this to the group with a cc to Bob Jones so the group can verify this or
correct it.
.020 on the bearing almost certainly designates a .020 under bearing, but
I did not understand why that is a problem. I would not put the old
bearings back in anyway; they are cheap, at least in comparison with pistons.
I'd borrow or rent a micrometer, check the crankshaft for size and
roundness, and check the pistons at the same time.
Ray Gibbons, Lurking in or
near Burlington VT
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