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Re: TR6 clutch forks and the bolt trick

To: "Power British Performance Parts, Inc." <britcars@powerbritish.com>
Subject: Re: TR6 clutch forks and the bolt trick
From: "Andy" <amdixon@erols.com>
Date: Tue, 17 Nov 1998 14:23:05 -0500 (EST)
Cc: triumphs@Autox.Team.Net
I should be so lucky.
Both TR6's I've owned had the fork welded to the shaft.
Andy D.

On 11/17/98 01:58 PM Power British Performance Parts, Inc. said...
>
>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
>---------------------------------------------------------------------
>     Power British                             Check out Power British
>    371 E. Main St.                                    on the 'net!
>Norristown, PA 19401
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