Edward Woods wrote:
> Mike and all,
>
> My '3's crank broke late one Sunday night just north of Folkston, Georgia.
> 'hiked back to base and returned for the car three days later. It was still
> there. That was 1965. Wonder if a car like that would wait 3 days in 2002?
>
> Have a crank downstairs that I had intended to use on my current rebuild.
> Shop found a crack when it was magnafluxed. Same place, No. 4. Believe it's
> a design flaw or perhaps an application error since it was not designed to
> run at high rpm's in it's original application.
>
> Maybe time for the TR racers to jump in on this subject.
>
> Ed Woods
>
Broken TR cranks are quite common. All TR racers are aware of it and broken
cranks and rods are what makes most of us keep our rpm's below 6000, which
delays
the failure. I have my stock crank magnafluxed every time I have the engine
apart
and average two or three seasons before it breaks. I've been lucky so far and
have not had one break at speed.
Besides the cranks now being 40 - 50 years old, there is a designed-in fatigue
failure feature. The undercut radius at the front edge of the rear main journal
is where the fatigue failure occurs. Picture this -- those four cylinders
alternatingly snapping the crank both forward and back, the rear of the crank
basically hooked to the ground, and the crank being subjected both to those
forces and to torsional vibration. Ugh.
Many of us try the shot peening - nitriding etc approach. This does not
necessarily eliminate the problem, as Henry Frye of Connecticut can attest to,
having broken a nitrided crank after 1-1/2 weekends. Of course, Henry's engine
was running so well at 6200 - 6700 that he drove it at that rpm. Until the crank
broke, of course.
--
uncle jack
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