CL007 CLUTCH

This thread had to have several corrections made by TW to his earlier contributions. After trying for a while to preserve the original so as to avoid 're-writing history' (and to illustrate how difficult it is to get a complete understanding of the design of the Velocette clutch....... !) a corrected version of the whole thing has replaced the original - TW

After a complete overhaul of the clutch I had noticed that the outer plate was pushing excessively against the chaincase despite the strict following of the adjustment procedure of the clutch. I thought that this would regularly reduce after some time, although only slightly, with the wear in of the friction pads. I had then a felt seal and too much oil ending on the rear wheel. I had therefore decided to fit the new silicone seal and it failed. I realized that before refitting the chaincase I had not oiled the seal lip nor the clutch outer plate and believe that this combined with the excessive pressure against the seal resulted in the lip being sheared off almost immediately. I therefore decided to fit a double thickness of the rubber/cork gasket to alleviate this contact between outer clutch plate and chaincase.- Gilles Glachant 8/11/2001

I do not like the sound of needing to fit two chaincase gaskets! This is wrong.
I can think of several reasons, mainly that you have a wrong component in the clutch - either a "sleeve gear distance-piece" that is too long, or the clutch plates are the thicker ones from the 7-plate clutch. But something is wrong, and we should try to work out what. - TW 

I am not too happy either with what I am doing just now. I will nonetheless test the present configuration which I have described to you.
In the meantime I would like to collect the information that I need to have for the next stripping down and check of the clutch. Such as: On a 7 plate clutch is there a specified length for the sleeve gear distance-piece? What thickness the plain plates should be?
My machine is a 1969 Thruxton which I acquired some time ago, nice looking but only nice looking apart from the engine which had been attended recently.
Other area of concern: Before summer I noticed that the first gear was rumbling, may be this word is not appropriate, but anyway it was making abnormal noise. I dismantled the gear box and understood why. Surface of the teeth was showing significant wear and the oil had certaining been acting as a good abrasive compound for some time. I decided to replace all wear parts, i.e. ball bearings and to replace also other gears. I acquired these but I am told around here that I should be careful because the steel used in these newly machine pieces is not as good as the original ones and is susceptible to break. Difficult question for you but I would be grateful to have your opinion. - GC

Gilles, I can give you some information that may help, but not everything.
The distance-piece for the S/A 9-plate clutches (and also for the early S/A MAC according to the manual), is the B35/3 which is longer (11/16" or 0.6875") than the one for the rigid 7-plate clutches (B35/2, length 5/8" or 0.625"). 
This presumably is to move the backplate on the 9-plate clutch out by 0.0625" for correct chainwheel alignment.
[The puzzle is that the springer MAC with 7-plate clutch seems to take the same, longer distance-piece as the 9-plate clutch. This is as in the Velocette parts list - and I found it was correct when I assembled mine, because it gave the proper chain alignment. One check you should make next time you have the outer chaincase cover off is the chain line - that will tell you if you have the right distance-piece.
The Velocette parts manual for the early S/A MAC specifies a 7-plate clutch (with the older, thicker inserts C25 and early plain plate C24 that has a different offset from the later C24/2 plate. Some people think the Velocette spec for the thickness of the two plates was the same whereas others believe the early plain plates were thicker). 
The later, longer B35/3 distance-piece is listed on the same page as the 7-plate clutch.
The puzzle is that this combination seems to give the correct chain-line on many early S/A MACs, such as mine.... 
Given that most of us believe that the sleeve gear bearing's outer face is in the same alignment to the engine sprocket on an early s/a MAC fitted with a 7 plate clutch as on a later MAC fitted with a 9 plate clutch and on a Venom, the position of the clutch chainwheel is determined by the combined thicknesses of the distance-piece, the back plate, 1 or 2 plain plate(s), 1 or 2 friction plates, plus half a friction plate to the middle of the chainwheel. 
The distance-piece is the subject under discussion, and the effective thickness of both KC1/25 & KC1/2 backplates is believed to be the same (the overall width of  its 'centre'  is the important difference, of course, being 1/16" longer for the KC1/2 in the 9-plate clutch). 
The inserts on the 9-plate friction plates are documented as C25/2 at 0.155" versus C25 at 0.195" on the 7-plate clutch. However the 9-plate friction corks that I have measured are 0.125" when new, and for a 7-plate clutch they are about 0.160", but who knows if an insert is 'original' nowadays?
Considering just the differences in plate numbers and thicknesses, and using the dimensions documented by David Childs in FT173 except for the plain plates whose thicknesses he doesn't give but my measurements show the steel plates for the 9-plate clutch are about 0.047" and though I do not have any from a 7-plate clutch outside a bike I think they are about 0.060":
For a 7-plate clutch: 1 x C24 plain plate @ 0.06"  plus 1.5 x C25 friction insert @ 0.195"= 0.353"
For a 9-plate clutch: 2 x C24/2 plain plates  @ 0.047"  plus 2.5 x C25/2 friction inserts @ 0.155" = 0.482"  
(Alternatively those new inserts I have measured have been more like 0.125" and 0.160" which gives total thicknesses of 0.30" and 0.4065 and so a difference therefore of about 1/10th of an inch.)
So the chainwheel centre is theoretically 0.10" or 0.13" further out on a 9-plate clutch compared with a 7-plate clutch, if the backplate thicknesses of KC1/25 & KC1/2 are the same.
So why is the same distance piece specified - unless 0.13" is considered immaterial in chain alignment, which would not be like Velocette even though it is of the same order as the movement that would result from major wear in the friction inserts. 
Since documentation says both used the same distance-piece on the only model that used both and that different backplates were certainly required, perhaps they did differ in  backplate thickness as well as in their centre width.? 
However examples of both backplates have been inspected and they do not appear to differ.....
With so many variables I think the main thing is to use the distance-piece that makes the primary chain alignment correct.] 
The sleeve gear nut and the thrust pins are also different on a rigid bike, but these would not alter the position of the clutch outer plate. 
You may have some thicker plates
Yes, I have heard that gears were made to poor quality for a period, but I have no facts. Nor do I know how the ones made today compare with the ones made by Velocette, which I believe were to a high standard. I think it is not only the quality of the steel but also the quality of the hardening. I believe the poor quality ones were made quite a long time ago, so if you bought yours recently then they will probably be of satisfactory quality.
However, if you like to ride long and hard you should definitely fit one of the club's B38M magnetic drain plugs and drain the oil every few hundred miles for a while, both to keep it good and clean and to check the oil you drain and the B38M for metal chips. There will always be some (mainly from the dogs) but if you get an increase it is time to look inside. It is anyway so easy to take the gears out for inspection on a Velocette!.....though not quite so easy to put them back. - TW

The current situation is now that almost all gears in the gear box are new. Bearings I have also replaced. All the plates of the clutch are new including the roller thrust bearing.
As explained before I have fitted a double thickness of cork gasket to reduce the excessive contact that I had between the outer clutch plate and the primary chain case cover which was disturbing the smooth handling of both the gear box and the clutch.
With this set-up which I will continue testing for some time before going back to normal gasket configuration, the result regarding the behaviour of both the clutch and the gear box is brilliant. Great pleasure indeed.
But there is a draw back. And that is the fact that too much oil is escaping from the primary chain case cover which I have so far been unable to resolve despite the use of various gaskets including the silicone that the VOC provides. Not surprised considering what I have done.
Whilst this provides a very efficient automatic chain oiling system I am now worried by the long term effect that oil can have on the rubber material of the tyre. Situation which is not infrequent judging by what I have seen on other bikes.
I would appreciate your point of view - GC 23/10/2002

Congratulations on achieving a good clutch and gearchange, even though you have had to use an unorthodox technique to achieve it!
I agree with you that it is best to test for a while before making any other change.
As you say, "everybody knows" that oil must not be allowed onto tyres because it the damages the rubber.
However, I had a Venom that I think leaked as much as yours does onto the rear tyre, and my only worry was that it would affect the grip. For me, it did not affect the rubber. Perhaps the warning applies less to modern tyre compounds. I just wiped it off after a long run.
Of course if there is too much, it will affect grip. My experience is that, when racing, and if the leak is not too bad, the oil causes little trouble because you are constantly using the sides of the tyre and so the tyre tread is kept clean by being in contact with the track before there is too much oil on it. You can feel the oil causing the tyre to slip when you are near the limit, but it is not dramatic. On the road, the problem is that you only use the side occasionally, and by then it is covered in oil...... Even so, you seldom go straight to full lean so part of the clean tread still works. But in the wet - it is dangerous.
I wonder if you also have oil leaking from the chaincase bolt? Unless you used a longer FK205 distance-piece, using two cork gaskets would either leave a gap, or if you fully tightened the bolt SL109/3 it could distort the case.
Other causes can be simply an engine that breathes out too much oil and fills up the chaincase so it then leaks out (it would also then flow into the gearbox and raise the oil level in the gearbox). You could test for this by putting only a very small amount of oil in the chaincase, and draining it after a run. If rather more oil comes out than you put in, you need to work on the engine - but meanwhile, just drain the chaincase after every run - it is better than it going on the tyre, and there will still be enough oil in the chaincase to lubricate the chain, etc.
Have you measured the clearance between the clutch outer plate and the chaincase with one cork gasket in? If this is adequate to allow the plate to lift, perhaps just use a felt seal that you have reduced in thickness to suit the gap? - TW 23/10/2002

Point taken about the oil on the tyre.
I have used the FK205 provided by the VOC. No leak there. The use of a thicker cork gasket certainly results in some deformation of the cover but this should be within its elastic limit and this latter should return to normal when I go back to a one gasket only. Regarding bolting I have has to use longer bolts and nuts. As some threads were poor anyway and had failed I decided to fit new bolts/nuts all around which enabled me to tighten and compress the cork evenly just as it should be and no more.
Reading various Q&A's I understood that engine breathing could be a real bother, so I have fitted some time ago oil levels on both the chain case and the gear box, (simply using reinforced plastic tube on a banjo union) in order to monitor this. No problem there. Indeed some oil goes into the chain case with time but very little and some regular draining does the trick.
I think I might have put too much oil in the chain case anyway as lubrication of the chain is beyond what I think it needs. I will adjust this down and continue testing.
I guess that the clutch friction pads will continue bedding in slightly for a little while. I will then address this question of the clearance between outer plate and chain case cover before returning to original configuration. The choice of gasket type will be decided then.
One thing appears now clear to me. The correct functioning of this unique and beautifully designed gear box and clutch assembly can really be spoiled by this tin box adjustment problem.
I will keep you up to date - GC 24/10/2002

I said that I would keep you up to date so here is the latest about the difficulties I add with the adjustment of the clutch and the chain cover.
Remember I had put 2 thicknesses of gasket to reduce to nil the pressure of the clutch outer plate on the chain cover when operating the clutch. This had resulted in a very pleasant operation of the clutch but with the unfortunate impossibility the stop primary transmission oil getting out and covering the tyre.
Having used the bike some distance I decided to revert back to the original configuration with one rubber/cork gasket only.
So I have used one rubber/cork gasket only with a silicone compound and tightened the bolts only slightly. I have also used the VOC soft felt seal.
Result is now that I hardly feel any pressure from the outer clutch plate on the chain case cover, Clutch operation is good and the soft felt seal does its job. It is not 100% oil tight and probably cannot be but it is certainly far better than what I had before. So hopefully I will not have to touch this again for some time. - GC 24/6/2003