Re: JPOR: Main bearings

[Ben Bargabus <ben_b@xxxxxxxxxxxxx>]

> 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.


I'd suspect the plastiguage first, recheck it.  If that's not the case
then it the last person to go through it may have accidentally gotten
one undersize bearing and not checked it or they may not have kept track
of which main cap was which.  The bearing could be in backwards (the
little tab not in the slot), who knows.


> 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?


Mic the crankshaft itself, there are specs for how worn or out of round
it can be before it has to be ground and the undersize bearings need to
be run.  Generally 401 cranks are very durable though (they are all
steel).


> 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?


For the non-thrust bearings wiggle them back and forth a bit while
pulling down and they will come out.  For the thrust bearing use a
plastic faced deadblow and lightly tap it out.


> 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.


You've gone this far, might as well replace the chain too.  If you've
got that kind of wear on the lower end I'd do the whole engine but if
you want to get by cheap and easy I'd at least do the timing chain,
cam/lifters (and their bearings), and oil pump.  That way you're not
paying for any machining but you're replacing the stuff that would be a
real pain to get to once this thing is back in the truck.


> 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.


Good luck,
Ben.