Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.
Q: I have a beautiful 1975 Norton Mark III Commando that is nearly unrideable due to a clutch/shifter issue that my local vintage mechanic has been unsuccessful at fixing. The clutch does not fully disengage when you pull in the clutch lever. The 1 to 2, and 2 to 3 upshifts are very hard, particularly when the bike is warmed up. Downshifting is worse, as pulling in the clutch to downshift does not fully release the clutch (i.e., even with the clutch lever pulled in, the transmission engages immediately when you shift down). Sometimes on a 4 to 3 or 3 to 2 downshift it hits what seems to be a false neutral, but sometimes blipping the throttle gets a gear to engage from the false neutral. To stop this quirky Commando I need to pull in the clutch lever, apply the brakes, and blip the throttle to “break” the clutch loose. Otherwise I’m “power-braking,” which is of course not ideal. Unfortunately, I lack the skills to troubleshoot and solve the problem. — Christopher Belling/New York
A: The Norton Commando clutch is usually pretty easy to set right, but there are a few things to check. First among them is the stack height, the total thickness of all the plain plates, friction plates and pressure plate. For your 1975 model the height should be close to 1.027 inches. If the height isn’t correct, you’ll notice it with either a dragging clutch like you describe or a difficult pull at the clutch lever. It’s possible that over the years there has been some mismatching of parts between a 750 and 850 clutch. The diaphragm spring and clutch basket are the same across the models, but the number and thicknesses of the plain and friction plates is different. For the 850 the friction plates should be 0.121 inches thick and the plain plates should be 0.080 inches thick, with the pressure plate being 0.102 inches thick. The 850 has five friction plates and four plain plates, while the 750 has four and three, respectively. Another common problem is a notched basket or clutch hub. This will tend to keep the plates in contact with each other even when the clutch is pulled in. To complicate things further, the plates can build up oil residue and stick to each other. On the right side of the bike, you should open the inspection cover of the gearbox to make sure of two things. One, that the clutch release lock ring is in all the way and tight, and two, that the cable to the clutch rod actuation lever hasn’t fallen out of position. It can fall down when the clutch pack and rod is removed. To make a long story boring, I think you’ll need to tear down the clutch and check everything to see what’s out of spec.
