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Thread: 1985 K100RS. Freaky front end.

  1. #1
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    1985 K100RS. Freaky front end.

    I took my bike out for a quick first ride of the season today and noticed the front end wanders-left, right, left, right. I can best describe the movement as twitching. It's as if I was very slightly pushing the handlebars one way and then the other. It didn't do it really at highway speeds but rather when I dropped down to something like 45mph and below, even really slow speeds like coming to a stop. It wasn't predictable and seemed to get better, then worse, then back again. It was kind of scary at times as it seemed to change. It was is if the front tire was pulling the bike one way and then the other. There is no vibration associated with the front end wandering. I don't know how to explain it any better than this.

    Winter work on the front end included Race Tech cartridge emulators and springs and upper and lower steering head bearings and races. I bought the tool from CycleWorks to do the latter. As it didn't do this last year then it is clearly as a result of something I have touched. I have just checked that all the front end bits are torqued and they are. The front wheel is not the wrong way around (tire rotation is correct).

    When I reinstalled the front forks after the emulators were installed, they were set at the correct length in the fork bridge and the front axle slid in easily all the way. I've blocked the bike up and moved the front forks fully left to right several times and it feels the same transitioning left to right and back again-neither tight nor loose. I've pulled on the front forks just behind the wheel and I can't find any looseness.

    Where should I look, guys, before diving in too far? What would cause this freaky front end movement?

    Thanks,
    Tom

  2. #2
    Registered User GTRider's Avatar
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    First thing to check is fork stem bearing adjustment. It’s not unusual to have new bearings seat in a bit during the first few hundred miles after replacement. Excessive looseness can usually be detected with the bike on the centerstand and front wheel off the ground. And having the bearings too tight can produce the sort of wandering you describe.

    Best,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  3. #3
    I agree with DeVern. Those symptoms scream loose steering head bearings. And as he said it is not unusual for the races to not be fully seated and to seat fully after a few miles. Some repair manuals call for them to be readjusted after 50 or 100 miles.
    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/

  4. #4
    Registered User jad01's Avatar
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    I would also double-check the front wheel itself to verify that there is no play at the axle or bearings.
    Jim (MOA 83200)
    '78 R80/7 (Anastasia) and '84 R100RS (The Millennium Falcon), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '97 Nissan XE PU (Mighty Mouse)
    '96 Giant Upland (big Kendas, baby!)

  5. #5
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    Just getting back to you guys on this. Yesterday, Sunday, I disassembled the necessary bits to get at the steering head. Once I loosened the large hex nut the steering freed up. That's not to say that it was really tight or bound up but rather that I noticed the difference. I moved the handlebars back and forth several times, checked for looseness in the steering head (there wasn't any) and decided that that freedom of movement was what I would go with AFTER tightening the steering head hex nut. It took a few attempts between loosening the knurled nut and torquing the hex nut before I got what I thought SHOULD be okay or at least a starting point. All done of course with the wheel attached. BTW, I did check the front axle, bearings, etc, while I was at it just to be sure a problem didn't exist there, although I didn't suspect there was.

    Fast forward to riding the bike. That was it. I had slightly over-tightened the new steering head bearings. Lost my touch I guess as it has been years since I had last done this. It was like riding a different bike! Thanks for your help once again, guys.

    Tom

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    Registered User GTRider's Avatar
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    Best,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

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