When I purchased the Triumph competition Dept. Spitfire Mk 3 (1969 FP champ)
from Kas, he said "DON'T go more than six races without replacing the crank.
Being budget-minded, I went six races and decided "Just one more."
The crank broke at #3 in practice for the seventh race. I still have the rod
as a paperweight - it has a nice hump bend in the middle.
Mike Cook
> From: budscars@comcast.net
> To: norlinengineering@comcast.net; fot@autox.team.net
> Date: Wed, 13 May 2009 17:38:06 -0700
> Subject: Re: [Fot] Broken Cranks: Was - Any connection between these
problems?
>
> I've broken 1 1296 small crank..that was after about 60+ hours on the
> engine..racing vintage..shifting at 6500 with occasional 7000..it broke in
> front of the rear main...
> my present crank is nitrited, and has about 20 hours on it
> Racer Bud..Spitfire #21
> ----- Original Message -----
> From: "Norlin Engineering" <norlinengineering@comcast.net>
> To: <fot@autox.team.net>
> Sent: Wednesday, May 13, 2009 5:22 PM
> Subject: [Fot] Broken Cranks: Was - Any connection between these problems?
>
>
> > Interesting to read this thread as I suffered a broken crank on my 1296
> > engine this past weekend.
> >
> > This is a small crank engine, prepared to SCCA limited prep rules for HP.
> > Shift point is 6800-7000 and max revs are about 7500, so the engine is
> > really not stressed that much. The crank was balanced, but not nitrided
> > or
> > shot peened.
> >
> > The crank broke between the #1 con rod journal and the #1 main journal
> > which
> > is totally weird. It's hard to tell looking at the two halves since they
> > beat on each other for a few seconds before I could kill the motor, but if
> > I
> > had to guess, there was a fairly large internal flaw in the forging that
> > didn't show up on the magnaflux test.
> >
> > I've been lead to believe that these cranks are virtually bullet proof,
> > but
> > now I'm not so sure. How many others have suffered broken 1300
> > crankshafts?
> >
> > The real bummer in this (besides the cost) is that I was leading HP in
the
> > National when the crank failed.
> >
> > "Helping to restore the economy thru racing" - Jim Norlin
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