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St4s Swingarm Pivot / Bearings

Discussion in 'Sport Touring' started by Turbogeek, Apr 5, 2020.

  1. Decided that I'd spend today looking at the only service job I'd never done since I bought the bike - checking and greasing the swingarm pivot and bearings.

    Got the 'pegs, clutch slave, chain cover, chain and rear wheel out, and thought everything was going really well until I tried to undo the nut holding in the chain-side cotter pin. The nut was just spinning round, on the partially stripped thread.
    With no room to get anything in underneath to split the nut off, I had to drill through the cotter pin from above using a right-angle drill, big enough (6.5mm) and deep enough (17mm) to break the stud portion off so that I could drift the large diameter portion out from underneath.
    20200405_113535.jpg 20200404_163017.jpg

    The serious over-torquing of the cotters has deformed the pivot shaft so I need a new one of those, and the bearings had play so they'll need to be replaced also.
    20200405_113954.jpg 20200404_163006.jpg 20200404_163000.jpg 20200404_163024.jpg

    Never straightforward, is it? I now have a unicycle, but at least being stuck at home means I have time to sort it properly!







    #1 Turbogeek, Apr 5, 2020
    Last edited: Apr 5, 2020
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  2. Ooh keep us updated.
    I'll be following this thread.:upyeah::motorcycleduc:
  3. Great job on drilling that out! Nice and straight etc! So it looks like the last person to do up the cotter just kept tightening until it stripped and then kept turning? Might even have been they were trying to get it off but were simply turning the wrong way until it was all over! Oh well, you are getting there, well done.
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  4. Good work, Not to hijack but I have around 1-2mm of movement on my swinging arm (right angles to the lenth of the bike) is this cause for concern?
  5. I'd say that was more than I'd be happy with, @johnny . But, it doesn't take much movement in the swingarm bearings to give that sort of movement at the wheel end.

    I've found that the bearings are shot, and also there's too much side-to-side play, due to needing additional shims between arm and engine cases.

    I've tested a 20mm ground steel shaft in the old bearings, and it slides straight through arm and engine cases, so it's not all bad. The bearings are rough, and I can feel movement/wear in them, so they'll be getting replaced.

    Moto-Rapido Aid Package is on it's way, so should have more to report soon.
  6. Yes, the old factory specification of tighten until it strips, then back 1/4 turn!
  7. If the movement is on the end of swingarm and vertical, I think you will find thats from the linkage assembly. I had that too but never could find a tolerance for the play...
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  8. Thanks, next winter maybe i shall take a look
  9. Got the necessary delivery of parts to tackle this task yesterday, thanks to the team at MotoRapido for their excellent service.

    First task was to clean everything so I didn't get covered in dirt whilst working. Used both Bilt Hamber Surfex HD and Bilt Hamber Auto Wheels to clean the swingarm, to get from this:-
    To this:-
    20200415_111442.jpg 20200415_110808.jpg
    Not perfect, but much better.

    Cleaning the inside of the arm revealed more evidence that not all owners of this bike have owned or had access to a torque wrench....

    So, then to start to remove the bearings and seals.
    First, the outer seals can be gently pried out:-

    Then the slide hammer comes out. Started with the first side one at a time,
    20200415_122233.jpg 20200415_122243.jpg

    But got braver with the other side and did them both together.

    I removed the inner seals, but left the circlips that go in the crankcases in place, no need to remove them. The case bores were cleaned and some marks lightly dressed.

    With that, time to start the rebuild - the inner seals go in first, be REALLY careful with these - the steel outers are very thin.

    Then it's time to drift the new bearings in using a suitable device (I used an old socket, no pics of that). Putting the bearings in the freezer for a bit, and heating the cases gently with a hot-air gun on medium setting proved helpful - if only psychological!

    Sometime later, after summoning up the courage and some gentle persuasion (BFH), we get to this stage on both sides:-
    Shiny new bearings and seals in!

    Then it's time to set the axial clearance between the swingarm and the crankcases, starting by putting in 1 x 1.8mm shim either side and measuring, then adding 0.1mm and 0.2mm shims as necessary. I ended up with 1 x 0.2mm each side, and an additional 0.1mm on the right.

    Swingarm back in! I still need some parts to fix some other bits (threaded bush for the bottom damper bolt was in really poor shape), but the bike can go back together once those are here.

    Overall, not as bad as I expected, but definitely needed the internal bearing puller/slide hammer.


    #9 Turbogeek, Apr 15, 2020
    Last edited by a moderator: Apr 15, 2020
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  10. Great write up.
    What’s the mileage on your St4s?
    The pivot shaft of my 888 was pretty worn and there was quite a bit of corrosion too. I just used the shaft off my St4s donor (along with the engine) when putting my 888 back together.
  11. It's on 47k. Didn't have much corrosion, luckily, which meant that the old shaft came out without too much of a fight, but the bearings were definitely worn.
  12. Thanks for the illustrated write up, I always wondered what that pinch bolt looked like! I tried to get mine out last year to grease the shaft but gave up since there was no side play. I have been lubricating them with various wonder products since but they still won't budge, I guess they must have been torqued up by the same chap who did yours 19 years ago. I think I will leave it a while longer.
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  13. Yes, they're interesting in that the hex in the top of the pinch bolt/cotter pin can mislead one into thinking it should turn. That hex is only for aligning the pin whilst the initial nut tightening is done, once it's drawn into position the wedge shape stops it from turning.

    I've also been told I have a mismatch of parts - the cotter pin arrangement should be a model-year 2003-on ST4s feature, but mine is a 2002 model bike (built 17/04/2002) but registered on an '03. Apparently other years of Monster did use this version of the ally swingarm before the ST range got it and my swingarm has a January 2002 date stamp. Either it was a mix-and-match to get bikes out of the door or the parts have been changed in the interim - always possible on a 18-year old bike!
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