GROUPS 5, 6, 7:- Gearbox
THE GEARBOX: This area is, I suppose, that with the most history behind it-for a start it is generally
referred to as the AMC gearbox as it was introduced when Nortons were fairly new to the AMC empire
and shortly afterwards it found -its way onto the AJS and Matchless heavyweight range, Before hat,
Nortons had a box with similar gears and an oval horizontal cover; this is known as the Norton-Burman
box and takes us back to about 1947. Before that even, almost identical gears were used in a box with an
upright outer cover -the positive stop mechanism was in the upwards bulge and before the war this
upwards extension had a separate lid of its own. This was the Sturmey Archer box, also used by other
makes such as Brough Superior. Sturmey Archer were a Nottingham firm, as were Broughs and they are
now part of the Raleigh organization. One sign of the antiquity of the design is the use of cycle threads far
studs and nuts. When you think that the AMC box was designed to cope with 30 bhp from a 500cc
machine, it is not surprising that on 828cc machines giving about twice the power the reliability of the box
is not what it should be.
SHELL, CLUSTER, SPROCKETS: The main items to note are: Gearbox Shell with Bushes and Studs-
often this part is supplied without bushes or without studs or completely bare. The shell should arrive with
seven studs, two dowels and two bronze bushes already fitted. Don't throw away the old case before
removing at least the studs, as cycle thread studs have something in common with Rocking Horse
substance. T he ends that screw in the case is BSF-just in case you need a helicoil they are easier to
find. Nothing wrong with the BSF threads, or cycle for that matter, in the right place. Better than this UNF
nonsense any day.
SLEEVE GEAR & LAYSHAF T BEARINGS: These two components are very close together and the metal
between them can crack-this will allow bearing rotation and gradual wear of the case. The bearings
sometimes rotate anyway; this can be recognized by a polished, not ground. surface on the outside of the
bearing when it is removed. No real cure-Loctite sometimes works and is much better than centre-
punching the case where the bearing fits (aaargh!) and much less complicated than having the outer race
of the bearing plated oversize. One of the first things to go on an 828--or even on many ?45's, is the
layshaft bearing in the case. First symptom of this is a kickstart shaft which moves round an its own and
springs back to dig you in the shin. At the same time you may get jumping out of gear. As there is next to
no side load fit a roller hearing equivalent, NJ203C3 If all else fails (which it easily can, once a bearing
goes) you can remove the layshaft completely and carry on in top gear only-make the change at the top
of a long hill though, as the kickstart will be inoperative. 'the other fault which can cause the kickstarter to
go round on its own a failure of the kickstarter pawl-we're coming to that!
Sleeve gear bushes axe always coming loose-sometimes the outer bush moves inwards to the centre of
the sleeve gear-then all you need do is to Loctite a now bush in the end. Leave the old one in and it will
prevent the new one moving inwards, i.e. fit three bushes in your 750 a la 850. Sometimes the bush
moves outwards and gradually mills itself away on the sharp edges of the circlip which locates the clutch.
That's worse because eventually the bush disappears completely and all the pull of the back chain comes
on the sleeve gear bearing. No wonder the bearings come loose. Often the first sign of sleeve gear
bushes going -is striking "gold" in gearbox or primary drive oil, watch it! Here the answer is to buy two
new bushes and a clutch location shim (060894 or O60895). Push both bushes-Loctited on the outside--
into the sleeve gear the middle one stops the outer from moving in-and then put the shim loose on the
shaft to avoid -the bush wearing on the circlip even if it does move. It is an advantage to grind the outer
edge of the shim so it will pass through the hole in
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