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  1. #1
    mtbr member
    Join Date
    Jun 2006

    Motor oil in semi-bath forks

    I'd been thinking about this for a while, and another thread on here prompted me.

    A lot of modern forks are now semi-bath, where, while there's a lubricating oil bath in the fork, the damper oil is separate from it. All Rock Shox with Motion Control or Mission Control are like this, as are the FIT equipped Fox32, Fox36, and Fox40 forks.

    Since the lubricating oil is now separate from the damper, is there a better choice out there than suspension oil? While it's good for damping, it might not have the best characteristics for a lubricating oil. I know several people who use motor oil in theirs' because it's designed to stick to internal parts better and has anti-wear additives (though forks probably don't hit the pressures and temperatures to make it relevant).

    So what's the word? Are there better, safe options than normal suspension oil?

  2. #2
    mtbr member
    Reputation: dascro's Avatar
    Join Date
    Apr 2007
    Jerk_chicken had all the background info on this, and I'm sure its posted somewhere but I don't really have the time to search for it and think it over again...

    But, my results are there are no noticeable differences when using motor oil vs. fork oil for this purpose. I've been doing it for several years in various RS and Manitou forks. It works just as well and is cheaper. I use Shell Rotella full synthetic 5w 40 without friction modifiers. I guess I only use that since its a very cheap full syn. that is known to be a great performer in atv and motorcycle engines. That way I only need to have 1 container of oil for my semi bath oil and ATV engine oil.

  3. #3
    Former Bike Wrench
    Reputation: mtnbiker72's Avatar
    Join Date
    Jan 2007
    Synthetic motor oil works good in warmer temps, but get the lightest available for Fox or RS forks (like 0w-20)...Manitou actually specs 5w-40 for their forks anyway. Synthetic ATF is a good option as its actually a tad lighter than even the lightest motor oil and is actually pretty close to Fox Fluid 7wt.

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