The Knowledge - Velocette Owners Club

E.3. Final Drive, Chains and Cases -
L #20 The only thing I want to do now on the MAC, aside from regular proper maintenance is to
find a relatively decent cure for the primary case leakage, which is pretty massive, even after a new
seal was put on. May resort to black silicon sealer.
#25 Most pin type p/chaincases distort finally, so you'll hit this problem with second-hand cases. I
wonder if belt primary drive might not be the solution, for Velo singles in general.
#28 I've been let down on the side of the road on a Velo have been primary chains, and both times it
was my fault. The second was trying to run an open case using spray chain lube, when I lost the oil
drain plug on a long ride. Au revoir to chain and clutch chainwheel both
#31 I was pondering that very thought recently, but though I have seen belt drive units for several of
the more popular parallel twins, nothing for anything so esoteric as a Velo single..
#34 There are two manufactures of belt drives for Velocettes one is by a guy called John Watson
telephone +44 (0)1768 898599, the other is Kevin Thurston telephone +44(0)1525 404699 – both I
have seen, but not used and look well engineered.
#71 I recently fitted a belt drive cum clutch kit onto my Venom. As the space inside the primary case is
very crammed, a bit of machining of the pulleys was required to get the required clearances. But
otherwise the kit was of unusual high tech quality and fitted straight forward and the back up help from
the manufacture was more than excellent. Clutch action is better and sharper, and neutral can be
found at standstill too. But do not expect a complete dry primary case. I recognized oil still collecting in
it as the crankcase blows always a bit into the p.c.c. and also some oil from the sleeve gear bush
dribbles in it. I fitted the belt kit because I got tired of cleaning the rear wheel and the garage floor after
a fast blast. I assume the Mac case and clutch is similar to the Venom, but Mr. Watson will know upon
these details.
#133 I've been in touch with Dave Smith of Dave Smith Classic Motorcycles, in Illinois, and he handles
the John Watson belt primary drive system. He is going to get back to me on my MAC, regarding
pricing, because there is little call for this system on the MAC, mostly the Venom, and I would need a
different ratio compared to the Venom, of course. Supposedly a good quality unit with no major
obstacles to installation besides replacing the clutch plates as the new basket will have friction material
as produced, so new plates would help guarantee proper function
#135 A word on belt primary drives. As we all know, the mainshaft breathes some oil into the primary
chaincase. But neither the belt primary drive, nor the dynamo/alternator belt drive really appreciate oil.
The primary chaincase also stops oil from getting at the generator drive. This should be borne in mind.
#137 Most of these primary belt kits come with a complete new clutch. A Velo clutch will work dry, or
wet, but not both ways in alternance.. From experience, the best pressed-metal primary chaincases
don't keep oil well enough, Velocette or other. The same chain, inside a good, oil tight alloy chaincase
gives no great problems. Years ago, I met somebody who had cast up an inner Velo primary chaincase
out of alloy, but retained the pressed steel outer. I meant to follow this up, but for some reason didn't.
#139 Glad you brought this up. I have wondered how the generator/alternator v-belt is kept from
slipping with the engine breathing oil mist into the primary case. The belt primary drive I am thinking of
is of the notched tooth variety, and some oil shouldn't affect it too much, especially as these new
plastic/metal core belts don't stretch basically, keeping potential slippage to an absolute minimum.
#140 I guess the cast alloy back half of the primary would keep it somewhat more leak proof holding
normal warpage over time to a minimum. Was this a pin or band type case? You see, this is one of the
things I love about owning this dear old MAC. While I can appreciate wanting to keep these fine
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