Main Bearing Journal Questions

[Stephen Bigelow]

Bentley says main journal diameter is
a) standard 57.958-57.978 mm
b) 1st undersize 57.708-57.728
c) 2nd undersize 57.458-57478
d) 3rd undersize 57.208-57.228

Bentley procedure for checking main bearing  clearance is to use
Plastigauge.
.0007-.002 mm clearance for new parts, .006 as a wear limit.



> Today I decided to check the bearing clearances in my 86' MC while it's
> apart.
>
> Problem, The main crank journal diameter is larger then that given in
> specifications in the Haynes manual I have.   This struck me as odd, since
> the specs for the pre 85' motors are supposed to be the same as the 86'
and
> later MC's.
>
> Next, all of the bearing clearances were WELL within tolerances.  I was
> recording a running clearance of .0011" on the first five and .0027" on
main
> number 6.  Well within the .006" limit.  Question is, since they're all in
> good shape, should I bother to replace them?  I don't really see any
reason
> to do it.  That was with the caps torqued to 48 ft. lbs, measurements were
> made using snap gauge and micrometer.
>
> Any BTDT??
>
> In regards to my big end bearings, I've been told it's a good idea to
> replace them regardless of their clearances.  What do you guys think?
>
> later,
> Will
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