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Thread: Clutch Friction Disk Original Thickness?

  1. #1
    RTNewbie
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    Clutch Friction Disk Original Thickness?

    Given that my friction plate is 0.210"/5.33mm in total thickness and averages 0.025"/0.635mm depth to rivet head and that replacement dimension (total thickness) is 0.177"/4.5mm, should I replace my friction disk?

    Does anyone out there have dimensions of a shiny new friction disk for comparison?

    If I do need to replace the disk, where is the best place to buy it? And why is the sky blue?

    Thanks

  2. #2
    Quote Originally Posted by RTNewbie View Post
    Given that my friction plate is 0.210"/5.33mm in total thickness and averages 0.025"/0.635mm depth to rivet head and that replacement dimension (total thickness) is 0.177"/4.5mm, should I replace my friction disk?

    Does anyone out there have dimensions of a shiny new friction disk for comparison?

    If I do need to replace the disk, where is the best place to buy it? And why is the sky blue?

    Thanks
    OK - I assume it is a BMW

    I gather from your screen name it is an RT of some variety.
    R80RT
    R100RT?
    K100RT
    R1100RT
    R1150RT

    Year?

    Then I can probably look the factory spec for minimum. They seldom provide a spec for new.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  3. #3
    Registered User AntonLargiader's Avatar
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    Quote Originally Posted by RTNewbie View Post
    Given that my friction plate is 0.210"/5.33mm in total thickness and averages 0.025"/0.635mm depth to rivet head and that replacement dimension (total thickness) is 0.177"/4.5mm, should I replace my friction disk?
    It's about 1/4 worn. New ones usually measure about .220. I'd keep it if the splines look good.
    Anton Largiader 72724
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    Virginia Motorrad Werkstatt BMW motorcycle service and repair in central Virginia

  4. #4
    RTNewbie
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    Quote Originally Posted by PGlaves View Post
    OK - I assume it is a BMW

    I gather from your screen name it is an RT of some variety.
    R80RT
    R100RT?
    K100RT
    R1100RT
    R1150RT

    Year?

    Then I can probably look the factory spec for minimum. They seldom provide a spec for new.
    It is a beautiful, brand new to me Pacific Blue 1996 R1100RT with 78,000 miles

  5. #5
    RTNewbie
    Guest

    Thumbs up

    Quote Originally Posted by AntonLargiader View Post
    It's about 1/4 worn. New ones usually measure about .220. I'd keep it if the splines look good.
    Great. As it turns out, there is precious little wear on those plates because they wear very slowly if properly adjusted and not abused.

    I was telling myself that more than 1/2 worn and I would replace it. 1/4 worn is OK with me as the splines show no significant wear.

  6. #6
    Registered User rxcrider's Avatar
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    North Ridgeville OH
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    Quote Originally Posted by AntonLargiader View Post
    It's about 1/4 worn. New ones usually measure about .220. I'd keep it if the splines look good.
    Am I correct to assume that 0.220" is the thickness of the new style clutch disk? The older (1996 in my case) ones were thicker and the pressure plates were correspondingly thinner - correct?

    EDIT:

    ...or not? I have my bike apart at the moment and have torn down my parts bike as well so I am staring at 2 sets of parts.

    The parts bike is a 1996 R1100RSL with the original clutch with < 21,000 miles on it.

    My bike is a 1995 R1100RS/RSL mut with a clutch that was updated in 2004 or later at an unknown mileage. It currently has nearly 80,000 miles on most of the bike including the engine and transmission. I know it was updated no earlier than 2004 based on the 2004 date stamp on the clutch (friction)disk.

    The pressure plate and clutch disk are the only parts in the clutch assembly which are different between the two bikes.

    The clutch disk thickness as measured on the lining over the rivets is ~0.210" on the 2004 clutch and ~0.190 on the old style disk from 1996. Now I don't know what each disk started out at or how much wear there is, but it is at least worth noting.

    The 2004 pressure plate is the same thickness as the 1996 part when measuring from the contact pads which touch the diaphragm spring to the clutching face. The radius (from the crank center line) at which the pads contact the spring is greater on the 2004 part. This would allow the pressure plate to sink deeper toward the flywheel creating a larger gap between the pressure plate and clutch cover for the same amount of spring compression. The machined step on the pressure plate which serves as a stop against the mounting pads on the flywheel is cut ~0.022" deeper on the 2004 part relative to the clutching face. Ths would make sense in relation to the change in contact pad radius, allowing the pressure plate to sit deeper into the flywheel without botoming out.

    Looking at the changes to the pressure plate, it would make sense for the newer clutch disks to to be thicker rather than thinner. This would also make the reports of using a new disk with an old clutch by adding shims between the flywheel and clutch cover (not sure which side of the pressure plate arms) make sense as it would work if the new disk is thicker.

    At any rate, the question of the original thickness of the 1998 & newer clutch disks still stands. If anyone knows if the 0.220" mentioned above is for the newer style or not, I'd love to hear.
    Last edited by rxcrider; 08-24-2011 at 03:47 AM.

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