BOS Deville oil change??

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  • BOS Deville oil change??
  • hugh_b

    Hi everyone,

    Have any of you carried out an oil change on your BOS deville forks yourself? I’ve purchased some 7.5wt Motul oil as recommended by LOCO on another thread. But just after some tips on completing myself such as oil quantities etc.


    orange 225

    I did mine recently, used fox 34 skf seals, the oil volume can be a bit of a faff, make sure you follow the instructions exactly though and make sure you bleed all the air out when refilling the oil.

    mr plow

    Orange 225 – Do you have any detailed instructions for pulling them apart? :mrgreen:

    mr plow

    It tells you about checking the oil height but I require a dummies guide to pulling them apart so that I don’t mess them up? :mrgreen:

    E.g. how to get lowers off correctly to clean them up and get all the oil gunk out?

    orange 225

    Rightio. Ill try remember.
    Let all air out of fork
    Undo silver adjuster (3mm Allen head)
    Undo grub screw on red adjuster
    Put bucket under forks
    Undu footnut (17 mm ish)
    Undo other footnut (5mm Allen)
    Before you totally undo them, tap with mallet to break the seal (with the 17mm ish socket on to prevent damage)
    Pull the lowers down a few inch and leave to drain
    Pull lowers off
    Cycle rebound rod to push the rest of the oil out
    Clean lowers and replace seals if needed
    (You can’t get bos ones without a service)

    orange 225

    To ref-fit
    Slide lowers back on
    Put footnuts back on and adjusters
    Undo rebound cap (red bit on top of right leg)
    Push forks fully down and lift out the rebound rod as far as it’ll go
    Get your syringe and oil
    Squirt oil into the rebound stanchion the push and pull rebound rod a few times to bleed the oil
    Keep repeating till its at the correct level
    140 = 60mm from bottom of threads
    160 = 50mm
    170 = 58mm
    All above are with the fork fully compressed
    Screw rebound cap back on
    Pump up and robs your mothers brother

    orange 225

    Also. Turn your rebound dial to its slowest as it makes it bleed quicker

    mr plow

    Excellent post, thank you for taking the time. I will probably smear about of grease on there for good measure while they are apart, spring side at least as it only has a small oil volume. 🙂

    orange 225

    No problem, yeah forgot that. Stick a load of grease in the gap below the seals. Good luck


    Thats great thanks!

    the manual mentions 5ml of 20w oil in the air side, i assume this is to go in the bottom of the leg?

    orange 225

    Yeah. I put 17ml in on j-techs advice

    Thread resurrection!

    I’ve had some dirt slip past the wiper seal on the air side so I’m going to do a lowers service myself rather than pay £70 for a service.

    Orange 225- YGM

    Update for anybody else who’s going to do this.

    I’ve been informed by the person who did this about the best oil to use:

    Apparently the oil BOS use has a 15.60 cSt@40C viscosity, and the closest thing to it is actually the 2.5wt form of Motul Factory Line (15 cSt@40A viscosity), not the 7.5wt, like most people use.

    Hope that helps somebody. I’m just passing on what I’ve told.

    For anybody that cares, the service is done and the fork’s back on the bike and plusher than it’s ever been. I think 5wt oil might be the way to go next time, though, because it feels like there’s less damping than there was before with the same compression/rebound settings. Or I might get a bottle of 7.5wt and experiment with mixing with the 2.5wt. Hope this helps somebody in the future.


    Great info on this thread – much appreciated.

    Just to add a word of WARNING to any Deville owners out there, DON’T believe the manual when it says only service the forks every 6-12 months. I’ve had mine for just over 6 months of not particularly hard use (I tend to use my winter HT in the real mud/slop etc) and thought I’d play it safe. Dropped the lowers and found a nice score mark along the length of the stanchion. From a brief telephone conversation, the chances of BOS warrantying this is next to zero so prevention is much better than cure!

    Oh, one more thing to add. The oil fill levels should be measured from the top of the stanchion/where the top cap meets the stanchion/crown, not the bottom of the threads.

    I’ve had a ride of my fork and it feels ridiculously plush and with the extra oil in the air spring lower leg, it should feel like this for longer now. I used some Fox 10wt Green because it’s one of the best out there for lubrication but any 10wt+ oil should do. I’ve had to add some more clicks to the compression and rebound so some slightly heavier weight oil is definitely the way to go.

    @fbk- Yeh, I took the service intervals with a pinch of salt and was planning on giving them some love before a year but getting that dirt under the seal meant I had to do it sooner.

    EDIT- The service intervals say you should do an oil change 1-2 a year but I’d do it every 3-4 months to be safe and make sure your fork is working at its best.

    Premier Icon guitarhero

    Another thanks for all the info. Thinking it’s about time for an oil change

    If you do the service with 5wt Motul Factory Line then would you mind reporting back on whether it feels like the right weight, as in your settings feel the same as before the service?

    Premier Icon guitarhero

    Sure thing 🙂


    Just serviced my Deville 140’s with Motul 7.5wt oil as recommended by Loco and replaced seals with the SKF low friction ones, they are super plush now, better than when new. Found quite a bit of dirt in the grease under the seal on the left leg so will be dropping the lowers every few months. I’ve been riding these since Christmas on average once a week but didn’t get out at all through March.
    You need a 21mm socket for undoing the foot nut, and to undo the rebound cap to put oil into top of leg is the same as a Fox fork (I think it’s 26mm socket)

    Really easy service and well worth doing. Cheers for all previous posts to help.


    Good informative thread, ta guys.
    One more thing on the to do list…!


    I also used Motul 7.5wt, if anything it feels like there is a bit less damping than with the original BOS oil. I’ve slightly increased my compression and rebound settings since the service. Slight wear on the air side stanchion for me too so I’ll be servicing them more regularly from now on.

    Have serviced my forks, oil change and new seals.

    Feel much better during use, but have some initial stiction when left overnight which takes a little shove to break.

    Any idea what the reason for this is?

    Premier Icon guitarhero

    Has everyone just been using the 7.5W for the air side also or 20W as BOS recommend. I’ve got some 15W if that would work. How about Fox Float fluid?


    Bit of a thread resurrection, but the instructions above worked wonders although mine seem to different sized bolts in certain places.

    I’m running 5w oil in the damper because that’s the lightest oil I had to hand. Likewise the oil in the sprung side us on 10w for now.

    The spring side had no oil in it whatsoever, so I put 17ml in the bottom as per the post above. Luckily after a fair few grotty rides and a dry spring side there is no wear that I can see. I’ll do them again in a few months but will buy the correct weight Motul oils.

    The forks feel smooth and are holding air so hopefully everything had gone to plan. The hardest part was getting the lowers back on.

    Cheers again for posting the above info.


    How the **** do you get the seals out of these!!!??

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