DISCUSSION ON FRICTION DRIVE PROBLEMS. (June 2009)
Over the years there has been some discussion on the material used for the friction drive ring on the countershaft pulley, and its operation. Nowadays, I don’t think any of the remaining bikes will be doing very many miles, but it seems that some owners on both US and English models have been experiencing difficulties, so here are a few thoughts.
IT IS ESSENTIAL THAT SUFFICIENT PRESSURE IS EXERTED BY THE TWISTGRIP TO PREVENT SLIPPING!
This is what the Handbook says:-
CLUTCH OPERATION.
When starting off, always see that the clutch is “well home”. Do this by turning left handle-bar grip well to left (right on US models!). As soon as machine is properly under way, release the clutch so that the friction wheel is engaged only hard enough to prevent slipping. A little practice soon gives you the right “feel” in this respect, but remember the point, otherwise the friction ring receives undue wear, and all the engine power will not be transmitted to the rear or driving wheel.
It’s also essential to have the rear drive sprocket shield in place – any chain lube thrown onto the flywheel will mean that it will slip. Some models have lost this shield during their lives.
Over the years I've come to realise that the bike is semi-automatic.
I just wind in the clutch fairly hard at the beginning, and then release it a little, just as suggested in the handbook, quoted above. BUT from then on I don't touch the clutch until I want to stop - I just move the ratio lever to the appropriate ratio without moving clutch twistgrip or throttle. I don't follow the handbook procedure, as it complicates things!
If it is impossible to get a good non-slipping drive with a high pressure, then there could be two causes:-
- Contaminated friction ring, which will mean replacing it
- Wear of the brass plate on the flywheel. I have a few examples where the plate has grooves that correspond to the 5 speeds. This plate can be reversed – indeed, this is mentioned as a selling-point in some of the original English Sales Brochures! So, does your plate have an unused face?
As to replacing the friction ring, that is easy to accomplish, but the material used on the original friction rings is not mentioned anywhere, as far as I can find! A few materials have been tried, but as yet none has been totally successful. These include a moulded polyurethane ring, water-buffalo leather, hard fibre, and MDF board.
There are still possibly FOUR materials to try. One is millboard/hardboard. This has apparently been used successfully – at least, there has been no report of it failing! If you look at the "6th Vintage Road Test Journal", printed in 1986, there’s a report by owner D. Wilson, in which he says:-
"The material looked like rings of millboard, super grade cardboard if you like. So why not try mill board? Ford cars use a lot of the stuff for interior lining. A visit to a car breaker produced enough to re-line all the Ner-a-Cars in existence, and for free. When clamped up the rings provided a solid mass which could then be trimmed down to size by spinning the wheel and applying a coarse file to the surface."
One owner is contemplating this now, after scorching his MDF ring while trying to climb Sunrising Hill – a gradient of 1 in 6.5 on the Banbury Run route - and a second owner experienced the same – both were on Model B’s.
The first owner is also contemplating having a ring made out of the brake block material supplied for the other vintage motorcycle rim-type brakes, but that may be relatively expensive.
A third material is as fitted to my Model A, which has had a replacement ring fitted, but it was done back in the early 1960’s, and the then-owner can’t remember what he used! I’m investigating the possibility of getting a piece forensically tested at my local University to try to find out what it is. This works VERY well, and doesn’t seem to wear very quickly at all. It has just easily climbed Sunrising Hill with absolutely no problems at all. It doesn't slip even in pouring rain with the engine cover removed!
The fourth material has also yet to be checked. I’m considering talking to Saftek, who supply brake linings, to see if they could bond a similar material to the original onto the outer face of existing friction rings. Of course, an old ring would be needed to try this, and I don’t have one. Any takers??
As far as wear is concerned, then provided your friction ring is proud of the aluminium friction wheel and the steel clamping plate by, let’s say, 1/8”, then unless you use the bike for commuting 20 miles a day, it should last you some time – by which time we may have discovered the best material!
If you have any comments to add, then please let me have them, and I'll include them on here.
SAFE FRICTION-DRIVING!