<VV> crankshaft cracking - breaking

[Tony Underwood]

At 09:27 AM 2/18/2007, djtcz at comcast.net wrote:
>http://home.hiwaay.net/~langford/corvair/crank.jpg
>http://www.elmnet.net/~lange_c/Talon%20Engine%20Rebuild/crank1.jpg
>
>The maximum stress in a crankshaft is usually the underside of the 
>rod journal in the radius.

This is an obvious weak spot in any crankshaft that's not radiused 
around the journals.


>These  Corvair  cranks' "arm" broke, but inspection of the failure 
>would show the crack started in the rod journal radius and with each 
>power stroke fatigued in a series of ratcheting increases until the 
>remaining area was just too small.



Oddly enough, the 'Vair cranks that I've seen break had cracked 
through the center of the arm (thus suggesting a fatigue issue caused 
by ringing) and had no "trails" leading to the journals.   Two of 
these broken cranks didn't have balancers on them, they had 
replacement cast pulleys.   They were 164" cranks.    I've not seen 
an early 'Vair short-stroke 145" crankshaft break.    The third 'Vair 
crank I saw that had broken had already been pulled down by the guy 
who ended up with the engine, already been partially "stripped", no 
idea of whether or not it had a balancer when it broke.


I do certainly agree that two things need to be addressed when 
assembling a Corvair engine, and that's to make cure the crank is OK 
to start with (Magnaflux) and use a good balancer on it.


tony..