Hi Douglas
Can't help with the bs number (though there are probably several materials
that would meet that spec) but 60-62 on the Rockwell C scale should damn
near put flats on the teeth of your file, I would think that one must have
missed the hardening treatment. The other thing to note is it says hardness
depth 0.75mm before grinding, in round numbers that is 0.030" or 30 thou, if
you then bear in mind to get the less than 0.0015" or 1 1/2 thou run out in
the overall length they (most manufacturers) would leave 0.010" to grind to
reduce the risk of scrap due to distortion during heating. Hey presto
instantly you loose 1/3 of the hardness thickness, though 0.020" should be
reasonably good for the task in hand.
Graham.
----- Original Message -----
From: Douglas Frank <frank@zk3.dec.com>
To: Triumph List <triumphs@autox.team.net>
Sent: Wednesday, March 15, 2000 6:24 PM
Subject: Re: Machine shop work
>
> Tony Rhodes wrote:
> >
> > I have 2 transmissions apart and
> > they BOTH have had layshaft failure by delamination of the hardened
surface
> > at the rear bearing near the 1st laygear.
> >
> > It would appear that the hardness of the surface or the depth of the
hardening
> > is not adequate for the force the needle rollers apply.
> >
> > I want to get my new layshaft hardened better (more?) (deeper?). Before
> > I make a lot of phone calls, is this something most machine shops can
do?
> > If not, then whom?
> >
> > Also, for those of you with tranny experience, is my impression correct
that this
> > area is a high failure rate area? This and the top hat bushing?
>
>
>
> FWIW, the layshaft on my GT6 was a total loss when I opened the box up.
>
> I bought a replacement from Rimmer-- it was included in their
> "reconditioning kit"-- but have decided not to use it.
>
> Rimmer's replacement wasn't finished to quite as high a standard as the
> original part, although it looked to be "good enough" and certainly fit
> well.
> The problem is that it's too soft. A layshaft ought to be "file
> hard." In other words, when you stroke a file across the part, it ought
> to skate along without digging in. My file bit right into Rimmer's
> part.
>
> I took the shaft to a local machinst who was recommended to me by a
> colleague at work, who is timekeeper for one of the local Busch light
> teams. The shop was unable to harden it, because they couldn't identify
> the material used.
>
> I ended up buying a properly hardened shaft from Quantum Mechanics
> (Monroe, CT)
> with whom I've dealt with before (and highly recommend).
>
> For future refrence, Rimmer's faxed me their specs for the shaft. I
> quote, without fully understanding:
>
> material ... BS.970:part3:212A42
> heat treat ... case harden 60-62 HRC, depth .75mm (pre-grinding)
> finish grind ... 4-6u c.l.a (that's 'u' for 'micro')
> tolerance (dia) ... 85 somethings
> max runout OAL ... .0015in
>
> If anyone can identify the US equivalent of that BS number, I'd
> appreciate it!
>
> --
> Douglas Frank Compaq Computer Corp. Friendship, n.
> ZKO 110 Spit Brook Rd. A ship big enough to carry two in
> 603-884-0501 Nashua, NH USA 03062 fair weather, but only one in
> foul.
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