[Fot] Gearbox thoughts

[Steve Yott]

I have had the opportunity to rebuild many TR gearboxes and a handful of
Stag boxes and would like to offer my opinion and that is what it is... my
opinion.

The Stag box added a lot of complexity to the area of the laygear and shaft.
The layshaft is different in that it has two outside dimensions that match
up to the spacers for the needle bearings. Now you have needle bearings,
spacers and thrust washers.  I am basically not a fan of this arrangement as
there are many more parts to fail and the needle bearings are known to fail.
Where the Stag laygear does benefit is from having two rear bearings!

The real problem occurs when excessive torque on the single rear bearing
causes the bearing and or shaft to fail.  Once there is play in the bearing
to shaft fit the laygear starts floating up, down and side to side which
then causes non-parallel loads on the bronze thrust washers and they begin
to fail.

I have bored a good number of laygears to install double rear bearings in
the rear of the gear.  I do not use the "open cage" bearing as the TR6 uses
but I use the TR4 type enclosed bearings.  I do this operation on all
gearboxes I rebuild now because I am sold on this fix.  The bronze thrust
washers will withstand the loads on them as long as they are square with
each other and the laygear end float is properly set and I use no more than
.006" of end float.

Just my opinion!

Steve Yott

-----Original Message-----
From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of Dean Tetterton
Sent: Thursday, October 15, 2015 9:20 AM
To: FOT Triumph
Subject: [Fot] Gearbox thoughts

Since we have been thinking about gearbox's. The Stag layshaft was changed
by Triumph to try and make them last longer due to the additional torque of
the V8. They added needle bearings in place of the brass thrust washers at
each end and an additional bearing  in the lay gear at the end where 1st
gear is. Has anybody tried this set up in a racing box? Does it help in the
wearing of the layshaft? 

The addition of needle bearings means that the spacing of the box inside
where the lay gear rides is greater. The needle bearings being thicker than
the thrust washers. This means that the Stag box is different inside. 
I have been able to make a tool that will cut the inside of a TR box to be
the same as a Stag. I plan to build a box using the needle bearings. Don't
at this time plan to put another bearing inside the lay gear. If I make the
lay gear deeper inside, I am afraid it will not be hard enough for the
bearings to ride inside. 

Before doing all this, has any body gone down this road before. If so what
has been the experience? 
Also any body with thoughts chime in. Is it worth the effort?

Dean T.

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