Clutch slipping when oil is "warm" not hot



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Thread: Clutch slipping when oil is "warm" not hot

  1. #1

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    Clutch slipping when oil is "warm" not hot

    so my 85 cb 650 i put a new clutch and springs in last year for this same issue and everything was in spec. until the oil get's hot after a good 15km+ ride it's fine but untill then when it hit's powerband 6,5-7k it start's to slip. I'm using Motul oil non synthetic. is clutch material oil temp sensitive
    Ride or drive anything but transit

  2. #2

    Re: Clutch slipping when oil is "warm" not hot

    Quote Originally Posted by Knight View Post
    so my 85 cb 650 i put a new clutch and springs in last year for this same issue and everything was in spec. until the oil get's hot after a good 15km+ ride it's fine but untill then when it hit's powerband 6,5-7k it start's to slip. I'm using Motul oil non synthetic. is clutch material oil temp sensitive
    No - a new clutch will not slip if the oil you're running is a JASO motorcycle spec.
    Something else is amiss, did you replace the steel plates at the same time or only the frictions ?

  3. #3
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    Re: Clutch slipping when oil is "warm" not hot

    I've run into clutch slip being temperature-sensitive on occasion ... Engines make more power and torque in cool weather, for example (because they're getting a denser air-fuel charge) and that favors clutch slippage. It's possible that your engine makes more power when it's warm enough to run decently but not completely up to operating temperature. (you have an air-cooled bike, they generally run hotter than we would "like" them to run)

    In any case, the clutch in your bike should have enough capacity to handle these fluctuations. Maybe it did originally, and now it doesn't, which means something's up. Maybe the springs don't provide enough clamping force, maybe your release mechanism is binding/jamming and not fully releasing (been there, done that), maybe you didn't replace the right parts, maybe your clutch basket is so badly notched that it's not allowing the plates to fully engage. (Look at the slots in the clutch basket that the tabs on the friction plates engage with) Or maybe you put something together wrong - forgot a spacer, parts put together in the wrong order, didn't check stack height and select-fit plate thicknesses accordingly (usually this is for "slipper" clutches but check the service manual), etc.

    On a yamaha fizzer, the pressure plate will go together 5 different ways, but only one of them works ... the one where the alignment marks on the pressure plate and the basket line up ...

  4. #4

    Re: Clutch slipping when oil is "warm" not hot

    1985 CB not on the original clutch cable is it ? <- possibly hanging up and not releasing completely
    :/ clutch pad material should survive heat as well as your oil does, if the oil burns your clutch pad material will start to burn. Is not suppose to get that hot in there, wet clutches should work and last pretty amazing.

  5. #5
    Robbo's Avatar
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    Clutch slipping when oil is &quot;warm&quot; not hot

    When did it start slipping? Just recently or last yr even after you changed the clutch and springs?

    What brand replacement parts did you install?

    How does it shift through the gears?

    Which Motul oil are you running in the bike and when was the last time it was changed? Using the correct type and weight is important in these older bikes. Iím asking for specifics because some oils work better than others for the older CBs.


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    Last edited by Robbo; 08-06-2018 at 08:14 PM.

  6. #6

    Re: Clutch slipping when oil is "warm" not hot

    Quote Originally Posted by Trials View Post
    1985 CB not on the original clutch cable is it ? <- possibly hanging up and not releasing completely
    :/ clutch pad material should survive heat as well as your oil does, if the oil burns your clutch pad material will start to burn. Is not suppose to get that hot in there, wet clutches should work and last pretty amazing.
    1985 Honda CB650 has a hydraulic clutch. IF the clutch master or slave cylinders were causing a problem the clutch would drag not slip.

  7. #7

    Re: Clutch slipping when oil is "warm" not hot

    Quote Originally Posted by TK4 View Post
    1985 Honda CB650 has a hydraulic clutch. IF the clutch master or slave cylinders were causing a problem the clutch would drag not slip.
    Sweet!

    might work for a couple of laps if you wash the plates off in some gasoline and then put them back in.


    How about water in the clutch hydraulics?
    Last edited by Trials; 08-06-2018 at 07:33 PM.

  8. #8
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    Re: Clutch slipping when oil is "warm" not hot

    maybe an old wives tale.....
    but were the friction disks soaked in oil for awhile first?
    not sure I believe it this, but I do it anyway

    wet clutches are definitely oil temp sensitive
    but not for slippage
    cold, think oil can cause drag

  9. #9

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    Re: Clutch slipping when oil is "warm" not hot

    Quote Originally Posted by JavaFan View Post
    maybe an old wives tale.....
    but were the friction disks soaked in oil for awhile first?
    not sure I believe it this, but I do it anyway

    wet clutches are definitely oil temp sensitive
    but not for slippage
    cold, think oil can cause drag
    No, some bikes, ST1100 being one of them, require friction disks to be soaked in oil before assembly, people usually leave them soaking overnight. If you don't do this you run into drag issues though, not slippage.
    PS

    2002 Honda ST1100, 1977 Yamaha XS750, 1975 Yamaha XS500, Honda MT250, Honda CR250, Honda CB450, Honda TL125, Honda CB175, Kawasaki G4 100 and Honda CT70

  10. #10

    Re: Clutch slipping when oil is "warm" not hot

    This bike has 6 friction, 5 steel plates and 5 springs. There's no way to mix them up.
    At the risk of repeating myself, were the steels replaced or just the frictions and springs ?

  11. #11

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    Re: Clutch slipping when oil is "warm" not hot

    the steels wern't replaced but everything was within spec. even the old friction discs were close to new thickness.
    the oil I'm using is Motul 3000 10w40 ma2 mineral. it did this even on the honda oil I was using last year.
    I went by all the measuments in the clymer manual
    Last edited by Knight; 08-08-2018 at 05:36 PM.
    Ride or drive anything but transit

  12. #12

    Re: Clutch slipping when oil is "warm" not hot

    Quote Originally Posted by Knight View Post
    the steels wern't replaced but everything was within spec. even the old friction discs were close to new thickness.
    the oil I'm using is Motul 3000 10w40 ma2 mineral. it did this even on the honda oil I was using last year.
    I went by all the measuments in the clymer manual
    Replace the steels, bleed the hydraulic clutch system and re-try.

  13. #13
    Robbo's Avatar
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    Re: Clutch slipping when oil is "warm" not hot

    Sounds like you are using a good motorcycle JASO-MA oil. Maybe switch the weight to 20w50 and see if that helps. 10w40 might be too thin.

    Have you done any work on the hydraulic clutch? The master and slave reservoirs can get gunked up. Also, there is a tiny pressure relief hole in the master cylinder (closer to the hose banjo than the lever) that can get clogged. Fluid canít return to the master. This can build up pressure in the slave cylinder as it warms up. This acts just like you are squeezing the clutch lever and can cause slippage. Something to look into.


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  14. #14
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    Re: Clutch slipping when oil is "warm" not hot

    Surface finish of the steel plates may be an issue. It needs to be slightly rough.

    Take them out, get a sheet of approx 100 - 150 grit wet and dry sandpaper, lay that on a flat surface, resurface the steel plates by moving them in a circular pattern over the sandpaper while applying a bit of pressure. Re-assemble.

  15. #15

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    Re: Clutch slipping when oil is "warm" not hot

    Ok I'll try sanding the steels before buying new ones. I just bled the clutch recently but even with the nasty old stuff it was still doing it. and of course since I have changed the fluid the master is leaking but a new one is on order.
    Ride or drive anything but transit

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