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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.


BSA Royal Star Jumping Out of Gear

Motorcycle Classics tech expert Keith Fellenstein 

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, 1503 SW 42nd St., Topeka, KS 66609, or send an email with “Keith’s Garage” as the subject.

Jumping Out of Gear

Q: I have a 1966 BSA Royal Star that looks just great. I bought it from the person who restored it. After I bought it, I took it easy on the old girl until one day I decided to give it a little more throttle. It jumped out of second gear, and it continues to do so every time I get on it. I have been advised that I need to readjust the clutch because the plates are dragging. I have played with Triumph engines and I have been into their transmissions before. I once had a 1951 BSA A10 Golden Flash engine and transmission all apart, but I didn’t have any transmission problems to deal with. I just replaced the bearings, seals, etc. I can’t understand what the clutch would have to do with it. If it is wear that is causing this, what would I look for and where would I look? From what I have read, I can take the transmission out without pulling the engine. I enjoy your column and would appreciate any help you could offer. — John Howlett/via email

A: The short answer is that it is highly probable that the gear dogs on the second-speed gear set are worn, and that is why it is jumping out of gear. I had this exact problem with a 1962 BSA Rocket. Unfortunately for us, that year was a one-year-only gearbox, so we had a hard time finding parts. You may be able to have a machine shop reshape the dogs in what is called an undercut, which is a slight machining of the dogs that produces a taper that pulls the gears together rather than forcing them apart. Otherwise, the solution is replacing the pair of gears that makes up second gear, and possibly the pair of gears that they slide into to engage second gear.

UPDATE: I spoke to John just recently after first responding to him, and in further discussion he told me that he found that the shift quadrant was worn and not holding proper position. In addition to that, he swapped around two of the gears that were identical, providing a new mating surface, and he now reports that all is well. I’ve seen problems with BSA shift quadrants in the past, usually leading to a poor or no-shift situation.

davidp
11/13/2015 8:49:45 AM

Yes, on A50 and A65 models the lay-shaft second and the main-shaft third gears are the same part. One can swap these to get fresh dogs to engage. Too much lay-shaft end float can also cause poor shifting. Many of these old dogs need the thickest thrust washer available. If you need this part be sure to measure the thrust washer before fitting. I have received the standard when ordering the thick one before. Best to be certain before assembly.