<VV> Nitriding was Oil Pump

Tony tonyu@roava.net
Fri, 07 May 2004 18:23:21 -0700


At 1653 05/06/2004 -0400, Ron Guy wrote:
>Snip
><Nitriding is surface hardening and is done in a tank so it will cover all
>of
><the crank AFAIK.  Primary benefit is in radiused areas of journals where it
><helps prevent crack forming-which lead to bigger cracks, etc.
><Chuck S
><YS73
>
>If Nitriding is surface treating then a 10/10 turned crank no longer has any
>benefit from nitriding.
>Is this sound thinking or is it more complicated than that?
>



That's about it.    Nitriding is a process done  via heating steel alloy to
the
point where it barely begins to glow and then spraying it with a fine mist of
an ammonia solution which causes nitrides to be formed on the surface of the
crank.   This nitride coating is extremely thin but then again it doesn't have
to be any thicker than a few ten-thousandths, if that much.   Its purpose is
not to strengthen the crank, it's to make it harder to scratch or score should
something get between the crank journals and the bearings, causing the debris
to get stuffed/sunk into the bearing material instead of scoring or scratching
the journal, which could cause galling of the journal and shortened life of
the
bearing and an eventual knock or spun bearing.    

Nitriding is considered a superior means of hardening a crankshaft over flame
hardening which involved a heating-quenching process which was relatively
expensive and time consuming and if not done correctly could cause cracks in
the surface of the metal... although flame hardening resulted in a *very* hard
surface which extended down as much as .01" into the metal, meaning that the
crank could be turned and not lose its surface hardening... *If* you could
turn
it without wrecking the machine tooling; the surface provided by correctly
done
flame hardening was indeed hard.   


No structural strength will be sacrificed if a surface hardened crank is
turned.   If the oil is kept clean and filters changed and nothing like
dirt or
crud etc is allowed to get into the oil, the surface hardening will likely
never be missed.   The nitriding done to Vair cranks was more of a "just in
case" measure than a requirement for engine reliability.   A lot of Vairs are
still running around today with engines that don't have hardened cranks.    



tony..