>My real concern is replacing the upper shell of the main bearings;
>Many folk in the V8 world believe I may have a problem installing
>the new upper shells and getting them to seat correctly; their advice
>is to just replace the lower main shell. Does this sound like
>OK advice?
Shane,
Replace the tops too. It is not difficult and they will seat just fine. I
did this a few years ago on my TR3, with advice from the list. When you
see the shells which come out, you might rethink your consideration of not
changing out the tops. Mine had fatigue pits and small chunks missing, but
the journals were fine.
The keys to replacing the bearing shells are:
1. absolute cleanliness,
2. using another shell half to slide the old one out, if you can't push it
out using something light, like a feeler gage. They only go in one way.
You may need to loosen all the caps a little and let the crank down a
fraction of an inch, to get the new ones in, but there should be no problems.
3. Generously use a good assembly lube on everything. I packed the oil
pump too, to make sure it pumped up quickly. I also disconnected the coil
and cranked the newly rebearinged engine until I had oil pressure before
firing it up.
4. Make sure you don't mix up the bearing caps or conrod ends,
5. Replace your thrust washers if they are at all worn. If you are up in
the tolerance range for clearance, buy an oversized set, combining the
standard and oversized to get what you need. Lap-in the steel backs of the
new ones, if necessary, to insure that you are close to the minimum
clearance allowed by the tolerance specification.
6. Any bearing cap bolts which do not thread in easily by hand should be
replaced. Since I did my conrods too, and several of the bolts were
binding, I replaced all my conrod bolts, $$$$'s ouch!
7. I don't know about a TR6, but on the TR2-4 engine, it is almost
impossible to avoid ripping the timng cover gasket, when you pull the front
bearing cap. On the TR2-4, this damage can be repaired with Form-a-Gasket
or RTV, but care must be taken not to let these materials get into a
position where they could be picked up by the oil pump. Again, the TR6 may
be different. I don't know.
Since you may have a worn crank, I want to share my "out of tolerance"
experience. During assembly, I used plastigage and determined that I was
just OUTSIDE the allowable wear limit after installation of the new bearing
shells. Since I was patching the engine, I was planning a complete rebuild
in the near future (this winter, two years later) I just completed the
reassembly. I was over the allowable wear limit by 0.0002 to 0.0005, but
my oil pressure is OK (20psi, hot idle.) I also did the conrod bearings at
the same time and they measured out fine after the new bearings went in.
Go for it. This is a nice straight forward job.
BTW - I queried the list about break-in when I did mine. The general
feeling was that since there is no metal to metal contact during operation,
unlike a piston ring, no break-in was required. Remember, once you have
oil pressure, the journals are running on a thin film of oil between the
journal and the bearing. It's only at startup that the bearing/journal
contact occurs, hence no break-in required.
Good luck!
Jack
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