On Sun, 17 Sep 1995, John Van Valkenburgh wrote:
> Whilst rebuilding my '72 MGB engine (18V), I had the machine shop turn
> the crank for me. They said that they turned the main and rod surfaces
> .010" for me. They also stamped that data on the crank itself. Tonight
> I finally get around to putting things together and using a .003"
> plastigauge I verify that the rod and main bearings are tight. So far so
> good.
>
> The thrust washers are .003" over and seem to fit snugly (no slop) while
> still allowing the crank to turn.
>
> The problem is that after I installed the main bearings and caps
> (taking care to lube the bearings with assembly lube), I can not turn the
> crank! I used a 2x4 and BFH and could *bearly* get any movement from the
> crank at all. I used care when installing the caps to make sure that
> nothing was crooked. The caps are not torqued to spec, but are quite snug.
> The bearings are make by AE, and are marked .010 so I think they are
> OK. My question is am I correct in assuming that it is likely the
> machine shop goofed and did not turn the main surfaces?
> Ideas? Suggestions? Sympathy?
Loads of sympathy. I once had the same problem when a machine shop
failed to turn any oil clearance on a chevy V8 crank.
But before you go back to them, you should try something. Torquing the main
caps to specs introduces stress in the block, which affects how the crank
fits. It's counter-intuitive, but the crank may turn easier after you
torque the mains than it does with them just snug. And let me know if it
works!
Your plastiguage readings should have been taken with each cap torqued to
specs. If the plastic imbeds in the bearing material, you have no
clearance. If it reads .003 on all caps, but the crank won't turn with
all caps properly torqued you have a serious problem--either the journals
on the crank or the main bearing seats in the block are not coaxial.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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