[Fot] Broken Cranks: Was - Any connection between these problems?

[RACER BUD]

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 at comcast.net>
To: <fot at 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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