> To align bore an engine as I understand it the machinist shaves the boss
> on the main cap. Then the caps are bolted in place and the mains are
> align bored. This results in mains that take standard bearings.
>
OK, that makes sense. The only problem with this approach is that the bore
may not clean up in the horizontal axis, because the original bore diameter
has only been reduced in the vertical axis. In other words, by grinding the
mating surfaces of the caps, the old bore becomes an ellipse with the major
diameter on the horizontal axis and the minor diameter on the vertical axis.
The major diameter will be the same as the original bore and the minor
diameter will be slightly less, depending upon how much metal was removed
from the caps. If the block is warped in both horizontal and vertical
axes, then it is possible that the new bores may not clean up.
I have used this technique (plus the techniques of welding up the ID, in
really badly worn bearings) in repairing pumps and gearbox housings on paper
machines and other industrial equipment in my somewhat checkered past, but,
after all these years, this is the first time I had heard of it being
applied to engine blocks. I've only rebuilt four or five engines in my life
and I never had a block that showed signs of warpage, so it has never
occurred to me that this approach might be required. It makes sense, and it
just goes to show, we can learn something new every day.
By the way, I have always believed that the correct term for this machining
operation is line-boring, because of the way the machinery is set up to
perform the operation. The boring bar is set up in such a way that all
bores are machined concentrically, in line, by supporting both ends of the
boring bar.
Michael Marr
1960 TR3A
Naperville, IL
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