CL001 CLUTCH

Why is changing down very crunchy, but changing up and selecting neutral is fine? - TW 10/6/2000

Probably because there is insufficient clearance between the outer clutch plate and the felt seal in the outer primary chaincase half. When you pull the clutch lever, the outer plate moves outwards. If it then rubs against the felt seal, it will be stopped from rotating. This is ideal when stationary, and doesn't matter too much on smart upwards changes. But on downwards changes you really need it to speed up not slow down, or the dogs will crunch. Try temporarily having another 1/4" slack in the clutch cable so that the plate doesn't get moved out so far. This will mess up everything else, but if your downwards changes are better you know there is a connection.  - Bob Higgs 10/6/2000

You're right, it worked. I checked the gap between the plate and felt ring with the clutch in and it was only a few thou at the left side, though it was more like 40 thou at the right side (clearly a less than perfect chaincase assembly or the felt wasn't seated at the left) and when I pulled the clutch lever I could see it pressing the felt ring and making the chaincase bulge out slightly. So I shaved a wedge off the left half of the felt ring and downwards changes are now perfect. I only needed to take about 1/32" off at the extreme left. 
So should the felt seal rub not against the plate to stop the oil getting out? - TW 10/6/2000

No, unfortunately most felt seals available for the last few years are too dense. The original Velocette seal was soft and could be compressed easily between the fingers and could therefore rub against the outer plate and not drag too much when the the plate moves outwards. The club spares scheme hopes to have some made of such material but until then all we have is the solid type. If you have one of the denser felt seals then you can only arrange it so that it catches the mist and the oil draining down the surface of the outer chaincase half. It mustn't rub on the plate. - BH 10/6/2000

I am tackling the problem of a crunchy downshift. I have read the comments about the felt seal obstructing the clutch freedom and went there first. This is my first time inside the chaincase of this bike. I found a rubber seal fitted instead of the felt. It has a lip which lies parallel to the primary chain and is attached at the inner edge. With the lip open the thickness is 6mm and closed 5mm. The chaincase pants when the clutch is operated. There is also an alloy spacer with O rings fitted round the center fixing bolt of the chaincase. The clutch is adjusted properly. Are the two items legitimate conversions please? - Ron Sabey 23/2/2001

If your chaincase "pants", you will get a crunchy downshift, for the reasons explained above.
Both the 'neoprene seal' and the 'O-ring' spacer sound like the ones the club supplies. The later usually works well - you can compare yours with the picture of the club one in the 'specials' picture in the spares section.
The neoprene seal is very popular with some people, and not with others. Possibly this is because for some chaincases it is too stiff and/or too thick because the cases are slightly out of spec, and unlike the felt it doesn't eventually compress or wear away, so the change down stays crunchy and the clutch action heavy. I would get a felt, and thin it down so it just kissed the outer plate. The spares scheme is working on a seal made out of a much softer rubber; but as with the softer felt seal it isn't the technology that is the challenge, just the logistics. - TW 23/2/2001

Update - the spares scheme felt seals are now made out of a soft, compressable felt.....like the Velocette originals. Soft rubber seals are expected soon. - TW 6/7/2001

Update - the VSL rubber seals are now made out of silicone rubber, and can seal without causing drag. They are a delicate precision moulding and they do need to be installed with care. The sealing edge of the new seal is not critical, but the fit in its chaincase housing is. The housing in your chaincase needs to be down to bare metal so that the seal squeezes in evenly, even a layer of paint will make it 'pop out'. It needs to be glued in with something like a silicone sealer after first removing any remaining coating of release agent from the back of the seal so the glue will work. Then make sure it is oiled lightly before contacting the clutch outer plate and starting up.- TW 10/10/2001