Triumph Bonneville Silver Jubilee Questions

A reader comes to Keith Fellenstein with a question about the engine on his Triumph Bonneville Silver Jubilee and general question on Triumph wiring.

Reader Contribution by Chuck
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by 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, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Triumph wiring

Q: I recently acquired a 1977 Triumph Bonneville Silver Jubilee. The engine number does not match the bike. I was able to contact the owner and he told me the engine was replaced by the Triumph dealer under warranty after only 200 miles because of a poor engine case casting causing oil to leak in on the points. Have you ever come across this? The dealer, Free State Cycle in Bladensburg, Maryland, is no longer in business, so I can’t contact them for confirmation. Any help would be appreciated. The bike has been sitting for a number of years and it is going to take some work to get it back on the road. I enjoy the challenge. There is nothing more satisfying than hearing a long dead engine fire up. Also, do you know when Triumph went negative ground?

Chuck/via email

A: At one time, dealers had access to unstamped cases for situations like this, but by 1977, with all the troubles Triumph was having, maybe they weren’t available anymore, or it was just easier and less expensive to do an engine swap. Today, we prize matching numbers, but you have to remember that at the time these were just motorcycles; no one was thinking they would be collectible someday. About the only thing you can do is just ride it and enjoy it. Sorry I can’t be more helpful. As to your second question, it looks like 1979 was the first year for negative ground. Triumph changed the shape of the regulator and they note in the parts list that it is negative ground and not interchangeable with earlier regulators. And I agree: Hearing one of these old beasts come back to life is inspiring. When I work on one for someone else, the look on their face when they hear it start up for the first time is priceless.

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