JPOR: Main bearings

[Obi-Wan <bvh@xxxxxxxxxxxx>]

Anybody out there know much about rebuilding AMC V8's?

I started tearing open the bottom of my 401 this weekend to see if
the main & rod bearings had anything to do with my dreadful oil
pressure.  After measuring the main bearing clearances with plastigauge
(the rod bearings will get their turn tomorrow), I was somewhat
surprised by what I found.  Spec in the TSM says .0017-.0020" for
bearings 1-4 and .0023-.0030 for #5.  I got:

1:  Much greater than .003, maybe .004-.005.
    Copper bearing surface is worn down to steel-colored metal in
    large patches on the lower half of the bearing.

2:  A little greater than .003, probably less than .004.
    One groove cut into the bearing, but otherwise in good shape
    with all its copper coloring.

3:  .002"
    One groove cut into the bearing (in a different spot than #2),
    with significant wear near each end of the bearing where the
    halves meet.
    The front side (thrust) bearing surface looked as though the copper
    surface had been burnt off of most of it, not worn down to steel
    gray like the main face of most of the bearings.

4:  .0015"
    One groove cut into the bearing (again in a different spot)
    with very bad steel-colored wear at each end of the bearing.

5:  .001" (that's right, one third of spec)
    One groove was cut into the surface with some not-as-bad
    steel-colored wear at each end.

The crankshaft journals all appeared to be in fine shape.

Crankshaft end play (controled by the #3 main bearing) was about
.010-.011".  Spec says .003-.008.  Note the burned thrust bearing
surface above.

I expected most of the bearings to be worn out wider than spec,
but what really weirds me out is how the #5 bearing managed to
become _tighter_ than the way it was from the factory.  Any ideas
what might be causing that?  The other four bearings were all
torqued down to 80-90 ft-lbs (the best I could do while maintaining
an accurate measurement) whenever I measured one bearing.  Actually,
I only know the torque settings of the bearing caps I'd already
replaced (I started from the front).  I used my impact wrench to
remove all bolts, so I'm not sure how tight they were to begin with.

Have any of you out there replaced rod & main bearings before?
The bearings obviously all need to be replaced, but with what size?
Since the #3 & #4 bearings are within spec, should I just get a
set of stock-size bearings, or do I probably need undersize bearings?
Can you get a mixed set?

Also, how do I remove the bearing from the bearing cap?  The TSM talks
about using a cotter pin to remove the upper bearing, but makes no
mention of how to get the lower one off.  Do I just whack the edge
of it a couple times with a screwdriver, or is there a more sophisticated
way of removing them?

Also, when the #1 bearing cap was off, I stuck a screwdriver into the
timing chain cover & roughly measured the play.  It seemed like it
flexed about 1/2", maybe a little more.  Hard to tell using that
method.  The TSM says 1/2" is the max before replacment is necessary.
Is that a hard & fast rule, or is 1/2" still functional?  What about
5/8" of play?  How much slop will a brand new chain have?  If enough
stuff needs replacement, I may just get it all in one rebuild kit from
PAW rather than piecing things together myself from local shops.

In case you haven't guessed yet, this is the most significant engine
work I've ever attempted, so all I know is what the TSM tells me.
Any pointers are appreciated.

				-- Obi-Wan
				   '95.5 YJ, '77 Wag (under the knife)

-- 
Ben "Obi-Wan" Hollingsworth                                   obiwan@jedi.com
Many people don't understand this type of devotion; in fact some think of our
mindset as a sickness or as an aberration of the human mind. -- Rick Pewe
              Anybody want to buy a Jeep XJ Dana 44 rear axle?