On 20 Sep 1995, A. B. Bonds wrote:
> In <Pine.SUN.3.91.950920140701.6913D-100000@northpole.med.uvm.edu>, W. Ray
>Gibbons wrote:
>
> >Which brings to mind a car question. If you have the main bearing caps
> >line bored (should that be "align bored"?) as Denise suggests, does that
> >enlarge the bearing holes? What do you do then? Are bearings made for
> >oversize caps?
> >
>
> Line boring (well, gosh, Uncle Ray, that's what the Old Farts at the
> machine shop call it) was a necessity for engines with poured babbitt
> bearings. With the advent of shell bearings, the necessity for this
> difficult and costly practice was eased substantially. In theory,
> once the block is line bored at the factory, replacement of shells
> should keep the mains in alignment. The big however is that one must
> always replace bearing caps in the correct slot (and the right way
> 'round). This is currently a problem for the chappie who has
> apparently mixed up some of his main caps over the years. One usually
> can find with careful inspection some marker (like punch pricks) on
> the caps to indicate to which journal they belong and well as the
> proper installation orientation. I cannot imagine a necessity to do
> line boring on the mains unless a bearing has spun, and I have never
> seen caps with oversize OD's, though such creatures may exist.
>
> A. B. "Boring is my middle name" Bonds
>
>
Line (align) boring does not make the "hole" bigger..... The machinist
removes a small amount of metal from the bottom of the cap then attaches
it to the block. The result is a "oval" shaped hole. He then line bores
the hole with a VERY expensive machine. The one drawback to this process
is that is DOES raise the crank centerline and it is important to verify
valve to piston clearace. But it can also have an effect on compresion
ratios!!
P.S. I agree that 'lign boring the block is often not necessary.
LEX
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