<VV> Unsual WAS Broken Crank!

[kenpepke at juno.com]

The failure of the crank that had been in aircraft use is most typical of the failures experienced in the majority of engines used in street use in both location and direction.  In this case the fracture travels in a plane normal [perpendicular] to the crank centerline, from relief groove to relief groove, and indicates a torque generated failure similar to an overtightened bolt.  These are seen in engines with and without 'vibration dampers' on the pulley end.  The problem was known to engineering so the early turbocharged engines had a special crankshaft.  These were coveted, in the early days, by builders of racing / high performance engines.  I do not know the failure rate of these special cranks.    

The crank in the original 'broken crank' post seems quite unusual in as much as one can see the fracture emanating from the balance hole wall and traveling generally parallel along the crank centerline.  One would have to conclude the fracture in this case was generated from the stress riser created by the off center location of the drilled hole.
Ken P


**************************
Marty Scarr <martyscarr at gmail.com> wrote:

It *does* look like the balancing hole might be the culprit, but I think
after the rods are removed and the crank is out, it will show a fracture
originating at the rod journal.

Pictures of another broken crank saga are here:
http://home.hiwaay.net/~langford/corvair/flexplate/problem.html

<http://home.hiwaay.net/~langford/corvair/flexplate/problem.html>Marty Scarr



On Mon, May 3, 2010 at 2:12 PM, Kinzelman, Andy <
akinzelm at greatnortherncorp.com> wrote:

> Guys,
> In my opinion - the balancing drill was too close to the edge of the throw
> - and made a weak point Look at it again).  Although it lasted a long time -
> it is still a weak point.
> Andy K.
> Wisconsin
 

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