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Thread: 91 r100gs tranny bearing question

  1. #1
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    91 r100gs tranny - bearings and upgrades

    Hello all

    I have a R100 GS tranny open to do the circlip on the output shaft and will be changing all the ball bearings while I am in there. Do not know the mileage, the gears seem to be in good shape and it shifted by hand fine before i took it apart. As well there was little metal fillings nor had he output shaft been affected by not having the circlip (front bearing still tight to the helical gear)... looks like a good buy off ebay couple of years ago for $150
    I plan to refresh this tranny, use it on the bike while I refresh the original that is in the bike now that is all okay except for having to always lift the gear shift after a gear down before being able to make another shift down; something not returning in the shift mechanism likely.

    Reading through all the articles that i could find and reviewing my configuration I would like some advise on which bearings faces to leave open to oil flow versus having seals in place, pictures on sites show different configurations.
    The configuration I found is all open both side except for:
    output shaft rear: both seals in place (I understand the outer one with the dry drive shaft, but should the inside seal be removed for oil exposure?)
    intermediate shaft rear: seal in place against the rear housing only.

    I also plan to replace the plastic shift roller with the recommended bearing skf 628/8 or 688 (8x16x5) - can anyone report that this makes a significant improvement for shifting?
    Last edited by grahamm; 02-19-2013 at 11:49 AM.

  2. #2
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    Guess little opinions out there on trannys. Going to stick to the seal configuration as found on the bearings and replace the plastic roller on the shift mechanism to a skf 628/8 bearing.

    Bearings in skf all tallied to about $110 and gaskets and seals to around 75. Getting output shaft to my favourite machine shop for the "groove" this week so when I get back late jan I can measure the bearing end play and then order the required shims... Hopefully it will be back together mid feb if the shims are stock locally.

  3. #3
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    Got the shaft done by my fav shop... 60 bucks got me the groove machined and the bit of metal removed from the top and bottom of the taper that came from the flange... Guess they welded themselves together a bit.

    Report from the shop.... Wholly crap that shaft was hardened, good quality heat treating and metal

    When I get the gaskets and seals in from max i will post up the reassembly pictures and full report of refresh cost.

  4. #4
    DaveM Dave Backmarker's Avatar
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    Transmission rebuild

    Graham, Suggest you look at http://www.cycleworks.net Dan offers bearings, tools and a video that includes fantastic tips on rebuilding an airhead transmission. I've rebuilt my R90S transmission and the tools, parts and advice I got from Dan's cycleworks site were critical to a great rebuild.

    DaveM
    1975 R90S
    2000 R1100RT

  5. #5
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    Quote Originally Posted by Dave Backmarker View Post
    Graham, Suggest you look at http://www.cycleworks.net Dan offers bearings, tools and a video that includes fantastic tips on rebuilding an airhead transmission. I've rebuilt my R90S transmission and the tools, parts and advice I got from Dan's cycleworks site were critical to a great rebuild.

    DaveM
    1975 R90S
    2000 R1100RT
    Good suggestion, thanks... I missed that video is available.

  6. #6
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    Got around to getting it all back together

    Circlip groove added to the output shaft:








    Shift mechanism plastic roller replaced with recommended Ball bearing:








    Housing, Cover and gear train all ready for re-assembly:






    To determine requirements for shimming I used the Solder method. 2.5mm solder installed without any shims, installed covere with spec'd torque. Dis-assembly and measured resulting thickness of the solder. Shim stack calculated with .05mm end play for each shaft - used .38, .28 and .2mm shims to get the required .05 end play. 0.2mm were special order from Germany all the others were stocked in the Canadian warehouse. Took about 2 weeks for them to come.












  7. #7
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    All buttoned up and lubed ready for installation in the bike:




    All back together and test rode around the block... silky smooth gearing now


    That was the spare tranny... next is the tranny that matches the bike.... this was practice

    Winter sure is long, can wait for the warm weather to come back. Now on to the Honda '78 XL100 clean up and winter maintenance on the KTM, Husaberg and wife's F650GS.

  8. #8
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    Total: ~$260

    $106 for new SKF Bearings including the little bearing for the shifter upgrade ($12!)
    $24 for shims ( hopefully I have enough to do the original tranny too)
    $62 for gasket and seal kit
    $60 machining of the Output shaft groove
    $2.14 circlip and locking ring

  9. #9
    Registered User PAS's Avatar
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    Grahamm, Kind of late to ask but did you notice much slop with the 5th gear when on the shaft? I have heard of guys needing to bush the gear or shaft. My 5th gear is like that after 160K plus miles.
    Great pics, thanks

  10. #10
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    Quote Originally Posted by PAS View Post
    Grahamm, Kind of late to ask but did you notice much slop with the 5th gear when on the shaft? I have heard of guys needing to bush the gear or shaft. My 5th gear is like that after 160K plus miles.
    Great pics, thanks
    Not sure of the mileage on the tranny I rebuilt but everything was nice and tight. I checked all the gears on the bushing and there was little to no play. As well there was no metal shaving in the casing.

    All good

  11. #11
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    Brilliant.
    Nice work. I hope to try this myself some day.
    Thanks for posting.

  12. #12
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    Very nice documentation Grahmm! I've used plasti-gauge before but never heard of the solder trick? Is that used in higher clearance (thicker) applications? I'm still stuck in the deep freeze in VT and have a ktm I should have put studs on to get some winter riding in. I'd like to put the lighting kit on her and get it registered this year.

  13. #13
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    Quote Originally Posted by saggs View Post
    Very nice documentation Grahmm! I've used plasti-gauge before but never heard of the solder trick? Is that used in higher clearance (thicker) applications? I'm still stuck in the deep freeze in VT and have a ktm I should have put studs on to get some winter riding in. I'd like to put the lighting kit on her and get it registered this year.
    Solder trick I picked up in one of the references for airhead tranny rebuilds. Other solution is to buy a gauge plate for around $90 which would avoid installation and removal of the cover for the shim determination. You install the precision gauge plate instead of the cover and then can make measurements to the bearing faces. Installation and removal of the cover is not all that bad.

    I love my KTM... The problem with me and my GS I always end up somewhere I should have the 250lb KTM I should also put studs on it to get through the winter... No room left for a sled

    VT... Love Vermont, my sister has a place at Jay... Know any good trails in the area for the KTM or the GS?

  14. #14
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    Some of the guys i ride w/ have lots of class 4 roads documented and mapped out for some serious dual sport riding. Alot is in central VT and the N. east kingdom area. Some of the connecting trails may be better suited for the katoom.

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