The Knowledge - Velocette Owners Club

B. The Engine
B.1. Bottom End and Crankcase -
L #198 Tony described the correct way to fit an oil seal to stop oil exiting the main bearing – now
I will describe a “bodge”, that a fellow club member used to fix the same problem. Clean the inside of
the sprocket with alcohol or some other solvent, place a circular bead of silicone around the part of the
sprocket that abuts the main bearing boss. Smear light oil on the main bearing boss, slide the sprocket
on and rotate at least one revolution. Lightly screw on the shock absorber, spring and nut. Leave it for
24 hours, before reassembly.
L #264 What methods have members of this group used to overcome slack oil pumps in
crankcases? I have just come across this with an engine I am building out of autojumble parts and I
am thinking of having the main oil pump body hard bearing chromed, anyone any comments .
#281 The only method I have come across but never used, is to sleeve the crankcase – a skilled
engineering job.
#364 You can use grinding compound on a plate glass plate to remove the wear on the oil pump base,
but I would expect a surface grinder to do a more efficient job. The only other problem I could think of,
was if the pump was slack in its bore then when the crankcase warmed up the differential rates of
expansion may allow air to be sucked into the pump. However I feel this would be unlikely.
L #369 Anybody know how to get the flywheel off a two stroke? The engine freed off in my U last
night, but that now means I can't lean on the stuck piston to undo the flywheel nut. My reading of the
engine section drawing on www.Velocetteowners.com is that the nut acts as an integral puller - or am
I way off the mark? Also discovered that the Mag appears to have automatic advance - hence no cable
for it. Despite standing for 50 years it still gives a (feeble) spark.
#370 I am not familiar with the model U but I did own a GTP. I believe the nut is separate from the
pulley/flywheel/sprocket assembly. If the engine is in the frame and the transmission is still intact, try
putting it in gear and applying the back brake while trying to remove the nut. It may work but no
guarantees.
#380 Thanks for the reply. I discovered that the pulley was just bolted onto the flywheel - a home mod I
think! The nut does however act as a puller for the flywheel, and I was able to both undo the nut and
break the taper fairly easily by jamming the crankshaft against the conrod with a block of wood.
Unfortunately I think I moved the flywheel round, so now have no idea where the Mag was timed at,
but I am sure there must be a fairly easy way to re-time it when it comes to rebuilding the engine.
#512 Here's my nightmare, from yesterday, which began when I followed the 'red book' instructions for
fitting the oil pump back into the crankcase. "Heat up the case around the oil pump housing using a
blow torch." Heat up? How hot? The BMS manual talks about "considerable heat". How considerable? I
broke a corner off the oil pump's cast iron base plate, by hitting it off axis with a hardwood drift while
trying to drive it back into the housing. A Good Samaritan, an old-time Velo expert, took pity on me,
heated the case, withdrew the pump, cleaned up the abuse, replaced the base plate and refitted the
whole thing. Now I know, having watched him, what considerable heat means. Blowtorch? Propane
gas flame? Forget it. He used a 'cool' oxy flame. Here's the drill as I'd now write it. Heat the crankcase
until it will easily char-grill a thick fillet of steak in thirty seconds. Continue heating until it is barely
possible to remain in the same room as the crankcase. When the sound of racing fire engines can be
heard, and the jaws on the vice are starting to melt, drive the oil pump into the housing. If it doesn't
drop in with one gentle tap, you need more heat. Iif the manuals had hinted at the very considerable
temperature needed, and given the hint that very little force is needed to insert the pump when the
temp. is correct, I might have saved myself a lot of grief and my mate a lot of time.
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