<VV> Hardened, (or Nitrided) Crankshafts

[Tony Underwood]

At 01:59 PM 2/12/2007, R. Stalder wrote:
>I'm new to corvairs so this is my first response to a question on 
>VV.  But I recently learned some stuff about cranks while building 
>my late model turbo engine.  So this is what I know, hope it 
>helps.  If your crank was originally nitrided from the factory, it 
>will have "&" type symbol stamped on the flywheel end.  If your 
>crank has been ground it will need to be nitrided again.  Nitriding 
>hardens the surface of the crank.  Grinding removes the hardened surface.
>
>However, I was told not to worry about nitriding my crank unless I 
>was racing or planned to due a lot of hard driving.  A non-nitrided 
>late model crank would be fine for normal daily driving.


A non-hardened crank will work fine for just about any race usage as 
well unless you get all freaky with supercharging and nitrous 
etc.    Even then there's not THAT much additional durability that 
nitriding will actually offer up.    It does help keep the crank from 
getting scratched up if there's trash in the oil etc.    In this day 
and age, that alone is enough reason to go ahead and use a hardened 
crank IF there's one readily available, but it's still just skim 
icing on a large cake for all intents and purposes.


By the way:

Remember that the *Entire* surface of the crank is hardened, via 
nitriding.   Of the Corvair cranks that I've seen actually break 
(seen several and they all came out of 140s), NONE broke at a 
journal, they all broke at an arm/throw.   Thus, turning the journals 
and removing the nitriding would NOT have been responsible for 
causing those cranks to break.    Now if there's a crank that was 
severely stressed and it broke at a journal, maybe that one might 
have been "saved" by the journals having been nitrided etc.   Or 
not.    Who's to say that it wouldn't have broken at the journal 
whether it was nitrided or not?

;)

  I'm still of the opinion that the nitriding is more useful in 
protecting journal surfaces than actually keeping the crank from 
breaking.    Surface hardening as a preventative measure to combat 
cracking is as much wishful engineering intent as it is actual 
experience...  no more, no less.

...still, it wouldn't hurt anything if the crank *was* hardened...



tony..