I just had to go through quite a bit of machining of the main bearings on
Peyote's original engine since I discovered during the teardown (after I
lost all the oil) that the center main bearing cap was broken (looked like
it had been for some time) and the crank had several cracks. So I bought a
steel crank, found a bearing cap, and turned it over to a good machinist.
He told me you can't simply line bore the mains by grinding down the caps
and boring, since that will inevitably move the crank upwards somewhat in
the block. Not a terrible thing with a pushrod motor and chain driven
timing, but nice to avoid.
So the machinist says he made everything right, including the obvious seal
problem. I haven't picked the bits up yet so I don't have a full
explanation, but I think he ground the cap ends just a tiny amount, and then
skimmed the bores minimally, cutting mostly into the caps. Then repeated the
process until he got a clean bore in all three bearings. At least that's
what it sounded like. then he made the seal holes round. Of course the rear
seal isn't much of a problem since I use the aluminum carrier replacement
seal kit--that kind of self-centers.
I'll quiz him roundly when I see the pieces.
I don't know how good the bearing alignments are in stock TR motors, but I
do know that we used to pull 25-30% more horsepower from british single and
twin cylinder bikes just by custom machining everything to be perfectly
aligned. Main bearings on most bikes were amazingly out of line and not
parallel to the other rotating parts (like the camshafts). Piston bores were
not remotely perpendicular to the crank. When you got everything right the
vibration almost disappeared, even with singles.
-----Original Message-----
From: WEmery7451@aol.com [mailto:WEmery7451@aol.com]
Sent: Thursday, June 22, 2000 8:02 PM
To: 'fot@autox.team.net'
Subject: Line Boring the TR-3/4 Three Main Engine Blocks
Dear FOTers,
During all my decades of destroying these engine blocks, I never had any of
them checked for perfect alignment of the three main bearing caps, or bored
to make the alignment more accurate. Bob Criss, who made the run-offs
several times, told me that he does not try to correct his mains since the
three main engines are normally straight. Bob Stanford who raced a TR-3,
and
then made the run-offs in a Morgan never line bored his blocks. Jack
Wheeler
mentioned recently that one problem in doing this is that the front and rear
main caps will be too short making it hard to seal in the oil.
My thoughts are that if I measure the main journals of the crank with a
micrometer, and attempt to measure the ID's of the installed new bearings
with a dial bore gage, I may be able to determine the actual clearance
between the crank and bearings (with some practice). Should the mains be
slightly misaligned, the actual measured clearance will not be there.
I am looking for the thoughts and opinions of the list on the advantages and
disadvantages of line boring the three main blocks.
Thanks in advance,
Bill Emery
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