Date: Wed, 14 Aug 1996 10:47:35 +0100 (BST)
From: paul gilders rs <enpjg@msiri.lut.ac.uk>
Subject: Re: Leland and Brit. Crankshaft Question...
Ralph Jannelli writes:
>I have my 80 Spitfire crank being done. I have to go .0010" under which means
>grinding. They told me that MG and Triumph cranks are only case hardened, so
>I would have to Nitrate (harden) the crank.....$250.00 to do it.
Just thought I'd chip in a little here - generally, as other people have
mentioned, grinding the crank does not necessitate a subsequent hardening
process. Hardening is accepted as being an additional process that will
hopefully reduce wear on the crankshaft itself and increase the strength
of the crank as mentioned by Michael Marr. It is my understanding that
cranks were not originally hardened at least not by nitriding or tufftriding.
Anyway, I have just recently had my TR6 crank tufftrided - basically for
the reasons previously mentioned and the fact that the crank is now down
to 0.030" undersize, which makes any subsequent grinding a little more
difficult (no bearings below +0.030"). I am therefore trying to preserve
what I've got as long as possible...
As I understand it, tufftriding is a process for cast iron cranks and nitriding
is a process for steel cranks (any more experience??).
As to the cost of tufftriding, it is normally based on the weight of the
crank. My TR6 crank cost me about 85 pounds to tufftride (about 125 US
dollars?) and since I would expect that a spitfire crank would be about
half the weight, I would think that $250 is extremely expensive. Maybe this
is partly due to the process not being tremendously environmentally
friendly which would probably make it more expensive in the US.
Finally, Michael Marr mentioned that the crank needs polishing after
hardening - this is true, although I don't think this is because the
journals grow. I think it is mainly to remove the carbony deposit
left on the crank after the process. Bearing in mind the journals
are somewhat harder than previously, it is not possible to take
very much off, even with emery paper. On mine I just removed any
machining marks and all carbony deposits and cleaned and cleaned and
cleaned.......
Anyway, for those interested, I just started up my rebuilt engine
this past weekend and I'm very pleased with the results. The engine
revs extremely easily (even though I've not gone past the running-in
stage) and has a great deal more power. I would seriously recommend
to anybody rebuilding an engine to get it balanced - it feels so much
better.
All I need now is electronic ignition, electric fan, K&Ns.......
Never satisfied....
Cheers,
Paul.
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