Technical Tips

British Motorcycle Rideability



Even today the Classic British machines are still very capable. 650 and bigger Twins are obviously better on the highways when needed although most classic riders will avoid the 4 lanes. A 650 Triumph, as with most British Twins, can easily cope with 70 mph cruising with a gearing change. The best place for your machine to be is at 3500-4000 rpm when cruising at 65-70mph. This is fairly easily done with a sprocket change. This is achieved by raising the gearbox teeth from the 650's standard 19, to 21. The 750 Triumph has 20 teeth and gives around 65 @4000rpm. It will easily pull the extra tooth. This 21-46 or 47 will give a much more relaxed feel to the engine at a given road speed. This will make the engine last longer, make your ride less vibey and get a bit more mpg. Some cutting is required to fit a 21 tooth sprocket to a 650-750 Triumph Twin but a BSA A65 is already notched to suit and they too will live longer and be more relaxing to ride. Off the line performance it not really affected that much. I have a 1974 650, stock except for Megaphones, it has a 21 tooth front and 47 tooth rear and with aggressive launches off the line it can still make the front a bit light and will still do 110mph flat on the tank. On a stock 650, a buzzy 60 mph at 4000rpm to 70mph at 4000rpm is a nice change.

Nortons are no different as a 750 has 19t up front. Go to a 21t on them and they will be a better machine on the road. An 850 usually comes with higher gearing: both can pull 22 or even 23 teeth but it is a bit more stressful on the gearbox internals. Norton boxes should be checked and upgraded, especially if you get a slap form the kick lever on the back of your leg, or you see the kicker flapping backwards under power. This is a sign that the layshaft ball bearing is collapsing and can be dangerous as it may lock the gearbox. Besides replacing the layshaft ball with a roller, fit a .020 or so shim in the kicker shaft to reduce layshaft end play and replace the first gear bush. This will help prevent jumping out of first gear. Put 3 bushes instead of 2 in the high gear and machine internal grooves for circlips. This will prevent the bushes from walking out. Of course replace any suspect bush or bearing. The gears wear rapidly on Nortons to a point so any hardening wear on the load face is not unusual. Also fit hydraulic seals for the kicker and gear shafts in the outer cover. If you are going racing or intend to give your Norton a bit of a hard time then an outrigger on the high gear might be a good idea. This helps reduce flexing of the mainshaft and will help keep shifts more positive. You would need to be able to lock the box in position: using a primary belt system is the easiest way. The design of the AMC and therefore Norton box is fine for 350-500's but is a bit weak for the 750's and bigger. Its main problem is the 2 piece layshaft. Triumph and BSA have full layshafts. The Triumph 5 speed boxes are a good thing and I put them in every custom I can afford to although be wary of the first few years. A factory redesign saw a complete new lay shaft assembly. The main culprits were the high gear layshaft and 1st gear layshaft dog. Dragging clutches can also cause 1st gear drop outs. An oil encased Norton clutch may need cleaning twice a year if used regularly.

On TRI -BSA I use the Taiwan plates and dress my pressed steel plates. You can get a 2 finger clutch with no slip or use of heavy springs by maximising the steel plate surface area. Use a thick glass plate or similar dead flat surface and some 400wet/dry paper to achieve this. Try to get 80% or more flat surface. You will be surprised how little you have now. More surface area means more grip and less pressure is required. Surface the pressure plate as well. Set the pressure plate runout (wobble) to as fine as possible and use standard springs. Never take the pressure nuts below the end, ie. don't expose the stud threads.