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[6pack] Crankshafts & Pilot Bushings

To: "6pack" <6pack@autox.team.net>
Subject: [6pack] Crankshafts & Pilot Bushings
From: "John Cyganowski" <janah@att.net>
Date: Tue, 26 Feb 2008 07:27:49 -0500
I may be a little late on this but for what it is worth.

The TR250 and 1969 TR6 were fitted with crankshafts of a different design. 
It is known as the "long backed crank".  The "long backed" crankshafts used 
a longer pilot bushing that fit inside the back of the crankshaft.  The 
flywheel for this crank was of a different design and cannot be fitted to 
the later style crankshafts.

The later "short backed" crankshafts ran from 70-76.  These used a shorter 
pilot bushing and the pilot bushing fit inside the back of the flywheel. The 
flywheel for the "short backed" crank is not retrofittable to the earlier 
"long backed" version.

The entire run of engines could accept either crank/flywheel pair (you could 
put the late crank in the early engine and vice versa as long as you used 
the correct flywheel/pilot bushing for the crank). It would be odd to find 
an early crank in a later car simply because there were so many fewer of 
these cranks made.

So Bob, the CF cars should have the short backed crankshaft with the pilot 
bushing in the flywheel. It would appear that you have the standard set up 
for your year.

All well and good.  Now when I took my tranny out to have it rebuilt, I also 
decided to change the clutch at the same time after all it is just 
incremental work. Now since I was already in there it seemed that it would 
be the time to pull the flywheel and have it surfaced and balanced and a new 
ring gear installed (and down the rat-hole we go!).  Anyway, my car is a 70 
and it has the correct short backed crank and the short pilot bushing. There 
was a slight bit of wear on the edge of the hole in the bushing where the 
mainshaft of the transmission is supported, so I decided to replace the 
bushing.  I ordered the the correct short bushing from Vicky Brit and it was 
different! The bushing should fit into the engine side of the flywheel.  I 
do not think it is supposed to be a press fit, rather I think it is supposed 
to slide in. The OD of the new bushing was 0.005-0.010" wider than the old 
bushing (1.000") and it would not fit into the flywheel. Additionally, the 
old bushing was 0.500" thick.  The new bushing was 0.455" thick. Thinking I 
just got a bad bushing, I ordered another one from Rimmer Bros.  It was the 
same as the one from Vicky Brit. Basically it does not fit either. Rimmer 
was not much help.  They could not explain the difference in the bushing 
sizes.  So I made a chuck from a bolt and a couple of grommets, chucked the 
new bushing into the drill and turned it down using some fine grit sand 
paper. So now the new bushing fits inside of the flywheel, but it seems a 
little short and I really do not know what I will do - use the old bushing 
or try the new modified one.

John Cyg.
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