BSA M50MX Under Water


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

Under water

Q: I have a 1972 BSA B50MX that was under water for 72 hours or more back in 1997 due to a river flood in Dallas, Texas. The owner couldn’t turn it over after several attempts, and at that point he just quit and sold it to me. He impressed upon me the main bearings were steel and must be replaced. It’s been on the back burner ever since. I’m hesitant to turn it over to someone without knowing what it really needs. I believe I could do it, but I also know older bikes have tricks you don’t get in manuals. Do you have any suggestions? 

Jerry Weber/Florida

A: Jerry, this sounds like something that won’t respond to my usual mix of solvents to free up an engine. You will probably have to use Evapo-Rust or Metal Rescue or something similar and allow them time to work their magic. Remove the spark plug and fill the cylinder and also fill the sump via the rocker boxes and pushrod tubes. Give it a week or so and drain the sump so as to not hydro lock the engine when trying to turn it over. Pull off the primary cover and using a proper sized socket on the crank nut, gently try turning the engine over. If it moves at all reverse the ratchet and go back the other way. Carefully working back and forth you should be able to free the engine enough to get things rotating. Don’t go too far though. Once you have the piston and crank bearings loose, you’ll have to do a complete overhaul as those main bearings will be useless from corrosion, as will many other moving, rotating and sliding parts.

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