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Thread: What Oils to Use for 1970 Bonneville T120R?

  1. #1

    Default What Oils to Use for 1970 Bonneville T120R?

    Just picked up my first Triumph; a 1970 Bonneville T120R. Have studied the Factory Workshop Manual regarding what oils to use in the crankcase, primary, and gear box. There's a chart listing "SAE Oil Grade" for each as follows: Engine Oil Tank 20 or 50, Gear Box 50, Primary Chain Case 20. I assume the 20 or 50 for engine oil is winter vs. summer. This seems pretty straight forward to me, and any good quality motor oil with these viscosities should do. But I thought I'd put this out there for any recommendations folks with more experience running these Triumphs might have. I know with my '67 Harley it says run the same oil in the transmission as the crank case, which I do, but I get differences of opinion on this. It seems like the Triumph book is saying the same thing. Any input would help as I learn this new bike.

  2. #2


    Hi James castrol 20w50 is recommended for engine and primary 80/90 gear oil for transmission. I would not use any synthetic oils in this bike ,some say synthetic oils wil allow needle bearings to slide rather then spin.Good luck

  3. #3
    Join Date
    Nov 2018
    Reno NV


    The engine breaths into the primary chaincase, so it should be the same oil as the engine.
    You should have an engine oil with high ZZP percentage as these motors use flat tappets.

  4. #4

    Default Thanks to Shovelhead68 and aumick10

    Thanks for your replies to my Triumph oil questions, which helps confirm some of my own research. Here's what I've decided to use: Brad Penn #1 20w50 Motorcycle Oil with increased levels of "zinc" (zinc dialkyldithiophosphate) for the crankcase. Castrol Hypoy 90EP for the gear box, which is exactly what the Factory Manual calls for, and I got from Rimmer Bros. in the UK, and Brad Penn 5w20 for the primary chain case. Everything I could drum up on the primary said to use straight 20w. My local NAPA store stocks the Brad Penn oils and tells me straight 20w oil is no longer made, thus the 5w20 for the primary. Thanks again for your replies. It always helps to have input from more experienced folks when starting something new. Speaking of far the bike starts on the first kick!

    P.S. An article I found on the British Cycle Supply Company website on oil recommendations talks more about the zinc issue, which apparently is reduced in current motor oils to be compatible with catalytic converters, and therefor, the recommendation to use a motorcycle specific oil with higher zinc content.

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