Peter Zaborski wrote:
> > From: Pete & Aprille Chadwell [mailto:dynamic@transport.com]
> > Sent: Tuesday, November 17, 1998 9:41 AM
> >
> > I'm still a little concerned with the fork issue, though.
> > Peter Zaborski (Thanks, Peter!) did confirm that there
> > are two styles of forks used on TR6s... His fork had
> > the boss cast into it and that's where he drilled into it.
>
> Just to clarify this...my fork looks pretty much like the one depicted at
>
> <http://www.sarnia.com/obsolete/catalog/tr/6clutch.html>
>
> And I placed my gr 8 bolt at the same place as the photo indicates. Not sure
> how long this will last (it's been about 4000mi so far) but it can't be
> worse than the pin on its own.
>
> > The only boss in the casting of the fork is the one
> > into which the taper pin is threaded. That doesn't
> > seem like much metal to me. Seems like drilling a
> > hole in that with a grade 8 running through might actually
> > cause the fork to crack and break apart if the taper pin ever
> > broke.
>
> Not to mention the problem of the pin and the bolt "crossing" each other in
> the shaft if I understand your description (I might be confusing myself
> though).
>
> Good luck Pete.
>
> --- Peter Zaborski CF58310UO ---
The fundamental engineering problem with the clutch fork is simply this:
The pin is tapered.
The cross-shaft has a tapered hole to accept the tapered pin.
The partially threaded bore in the fork IS NOT TAPERED!!!
What this means is that contact is made on only one side of the fork pin. (the
side
nearest the threaded portion just below the head) All the force is
concentrated at
that spot and the pin will ALWAYS break at this spot - never anywhere else.
The best,
albeit not so easy, solution is to ream the hole in the cross-shaft to the same
diameter as the bore in the deepest part of the fork. Then fabricate a new
pin, one
with a straight shank of corresponding diameter + .001" for an interference fit
that
will tightly engage both sides of the fork. No modifications are made to the
fork,
but now the shear force is divided equally between the top and bottom of the
new pin,
which is also slightly larger in diameter than the original tapered pin.
The real benefit comes from the fact that the topmost portion of the pin extends
directly up into the right-hand finger of the fork, thus there is no chance of
overstressing or cracking the base of the fork around the shaft. I know it is
not
exactly a do-it-yourself prospect to make such a set up, but we feel this is
the best
way to insure never having to do that job twice! :-)
Regards,
Brian Schlorff '61 TR-4 '64 TR-4 '72 TR-6 '79 Spit
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