Alu chaincase gasket

[Biscuit]

Tom, whilst you have the chaincase off, it is well worth your while to check the tightness of the clutch centre nut. The clutch centre, or more accurately, the'spider', is held against the mainshaft splines by small inward extensions of the male splines in the spider, a ridiculously small area. Fretting at this point allows the centre to move towards the G/Box and eventually the clutch centre backplate rubs against the inner chaincase. In one bike I worked on there was so much wear that the clutch centre was locked against the sleeve gear, making neutral engagement from rest extremely difficult.

If you spin the clutch with it disengaged, either via the K/S or running the engine, the clutch basket and chainwheel will wobble about, this is normal, as it it the clutch plates and springs that hold the basket in its appointed position. Brilliant is it not?

Is this your first twin? I seem to have a picture, entitled 'Tom Mortenson' standing by a twin.Edited by - Biscuit on 02 Jul 2007 09:53:00 AM

[TommoT]

Alan,
I will check as you suggest. Incidently one of my first mechanical disasters as a Matchless owner was setting out for International Jampot Rally in 2001, when about 20 miles from home, the clutch lever suddenly came all the way to the handlebar without any resistance. I continued a bit until suddenly I heard a big clonk, and all propulsion was gone! Upon investigation the clutch had come completely off the gearbox shaft, resting at the bottom of the chaincase. Miraculously nothing was bent or destroyed, so I simply refitted the clutch and centre nut and continued after about an hours work!

My 1956 G80 has a different chaincase, different clutch and gearbox, so any hints and tips about the twins will be of help to me. I have had the chance to look at and stand by a twin, but never had one or ridden one before this.

I have done about 150 miles this weekend, so I am getting to know the old girl. I really love the sound and instant pulling power, but a completely different feeling from my G80. She does seem awfully low geared though. She goes through the 4 gears in short order, ending up buzzing along at 60mph. I've taken her to 80, but it sounded and felt scary, so I'll leave till later.

My next task is to take the primary chaincase apart, clean it up a bit and reassemble in order to make it as oiltight as possible. It does leave a small puddle of oil directly under the joint of the two halves, so improvement must be possible. My G80's steel chaincase is much more oiltight, leaving only a drop or two after a high speed (relatively speaking!) stint.

I'll probably keep you twin gurus busy over the next few months until I have sorted out a few small problems still waiting to be solved. Thank you so far

[Don Madden]

Hi, Tom. When you have it apart, check for damage to the cases. If neglected, the chain can break, piling up all the links against the deflector cast onto the back of the back half. This can crack it & if welded without fastening both halves together, will distort it.

I can also crack the outer case causing a drip.

I have just repaired such a case on a battered scrambler, (not mine). Besides battered, distorted back half, there was a hairline crack in the outer, at the bottom, of course.

Cheers, Do.