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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

Leaking Fork on a Triumph Trophy 500

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 e-mail with “Keith’s Garage” as the subject.

Leaking Fork

Q: I just completed a 5-year restoration of my 1971 Triumph Trophy 500. My problem is a leak on the left front fork. It appears to be leaking from the small bolt that holds the bracket for the wheel. I’ve tried some black RTV on the threads and also teflon tape with no success. What can I do? — Al Rieske/Reno, Nevada

A: There are three potential leak points here. Two of them are likely and one unlikely. The first is the drain screw and sealing washer. You can get fiber or copper washers for these; I prefer to use copper. Make sure the sealing surface on the fork leg is clean and flat. Often, if a fork slider has been powder coated, the coating will cover the sealing surface, making it difficult for the sealing washer to seat. The second likely source is the bolt at the bottom of the fork securing the cone-shaped restrictor inside the fork slider. The restrictor provides a hydraulic lock at the extreme end of fork travel, stopping the forks from bottoming out metal-to-metal. There is tremendous oil pressure in that space at the extreme end of fork travel. If the aluminum sealing washer is worn out, you will often find a leak here. You may be able to retorque the bolt holding the restrictor, but a permanent solution will be a new crush washer. The final and least likely leak source would be if the studs holding the axle cap had been over-tightened and either cracked the stanchion or pushed through into the oil chamber at the bottom of the stanchion. NOTE: A follow-up email from Al indicated the leak was indeed from the bolt securing the restrictor. Retorquing the bolt fixed the leak. MC