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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.


1968 Triumph T100S Fork Oil Questions

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.

Fork oil questions

Q: I have a 1968 Triumph T100S and want to change the fork oil. I have taken the drain plugs out of the bottom of the fork legs and will let the oil drain for a day or so. For refilling, I have a few questions: I assume I take the nuts off at the top of the triple tree. My manual says to add 190cc to each leg. Do I just pour the oil in the top and replace the nut? What oil do you recommend to use? I have Harley-Davidson fork oil from my old Shovelhead days left over, would that be OK? Some people have advised to use ATF transmission fluid, but I don’t want to mess this up. John Schaub/via email

A: In addition to pulling the plugs and letting the oil drain, it’s helpful to pump the forks to get even more oil out. Unfortunately, with the drain holes pointing left and right, pumping the forks just about guarantees spraying oil all over the place. Once you’ve emptied the forks as much as possible, you do indeed just pour the oil in the top. You should either put a jack under the engine to support the bike while you remove both caps, or take the easy way out and just remove and replace one at a time. Either way you’ll have to compress the spring to get the cap back on the fork tube. That’s easiest if the bike is jacked up so the least amount of load is on the fork springs. Take your time pouring the oil back into the fork tubes as the oil will collect in the spring before trickling down into the lower stanchion. Your Harley fork oil should be fine, too, providing it’s 20w fork oil. After 1972 Triumph recommended ATF for fork oil, probably because is was a similar weight and easy to source. MC