Brian Schlorff sums it up nicely, in that the original fork bore doesn't
share the load thruout the taper. But...if one were to start fresh and
make a new tapered bore thru the center boss of the fork casting as
Don's post described, it could be better equipped to carry more of the
load.
I'm not sure if this approach is worth the extra effort or not. Consider
that if the original tapered fork pin design is rebuilt with a new pin
(with no stress-rising machine marks), and placed into a new (unworn)
clutch crossshaft, then adding a second pin should split the load. In
such a case, any good method of adding a second effort may suffice.
I have used both the roll pin and the Allen bolt as the backup. The roll
pin can be a nuisance to install and remove, so I now use a 1/4 inch
Allen bolt. This long-shanked bolt leaves no threads under stress inside
the bore, and is a tight fit. Washers and a nyloc nut secure its
position. I have yet to hear of a failure in this area since doing this
over the last five years, on four different TR6's.
My own TR6 now has NO fork or pin, cross shaft or slave cylinder, but
that's another story!
Dick
Here is another gem I saved from Brian Schlorff (Power British) when I
used to subscribe to the big triumphs list:
start <<<<<
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! :-)
end <<<<<
Peter Zaborski -- CF58310 UO
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