Bill Munts wrote:
>
> On 8/7/96 10:58PM, in message <960807235550_173694274@emout13.mail.aol.com>,
> Metwrench@aol.com wrote:
>
> > Hi Gang,
> >
> > Have any of you had a crank ground down ? Has the machine shop told you that
> > after is was ground that it would have to be hardened ?
> >
> > I have my 80 Spitfire crank being done. I have to go .0010" under which
>means
> > grinding. They told me that MG and Triumph cranks are only case hardened, so
> > I would have to Nitrate (harden) the crank.....$250.00 to do it.
> >
> > I could take a 50/50 chance on non hardening , but no warranty.
> >
> > Any advice group? or stories on this?
> >
> > John P Spofford
> > 80 Spit.....
> >
>
> Hi John,
>
> I had the crank on my '70 Spit ground .0010" under and didn't have it
>hardened.
> The machine shop didn't mention it and I never thought of it. The engine has
> been running great for 3 years now. Either my crank is wearing away or your
> machine shop is incorrect.
>
> Bill M.
> '70 MkIII Spit
Back in the 60's, in Jolly Olde England, the standard approach to tuning
the bottom end of an engine was to grind the crank, nitride (actually
"tuftride" was the name of a proprietary process, as I recall) and
then polish the journals before balancing. It was thought that the
nitriding process not only hardened the crank but also added a little
strength and stress relieved the crank. The nitriding process makes
the journals "grow" a little, which is why the polishing step is
required. When I rebuild my TR3A motor, I will definitiely go through
the nitriding step.
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