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  1. #1
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    Spitfire - Custom bushings/shim fix

    I bought a 2009 Spitfire last year with lots of miles on it. The guy who rode it... rode it hard, but it was still in good shape. I'm talking 300-500 hard rides. I put it through the ringer this year, I'm estimating at 130-150 rides. I replaced bushings twice. The last time I replaced them, I only got about 2 weeks before the frame was clapped out again. The right side of the sub pivot (the pivot behind the main pivot) was over-sized, and causing the IGUS bushings to wear prematurely. If I had to speculate on why it was over-sized, I would say the nut came loose and the pivot was running wild for a ride or two. It really wen't downhill fast, whatever it was. Any side impact really stretches that hole out too.

    I work as an engineer in an unrelated field, and have access to a full shop, so here is my take. I yanked the link off and inspected, and found about .015inch difference on one side. This was causing the axle to wobble around and wear things out. I thought about machining a new link (which I may still do), but decided on shimming the hole to fit the axle. Its just a simple 6061 aluminum shim with a .0065 wall thickness (I have one hell of a lathe).




    Inspecting the rest of the pivots, I found wear in just about every spot. I pulled dimensional prints from IGUS (Banshees bushing company) and realized I would need something custom to take up the slack in the distortion fits. I went with Turcite A (blue stuff) for the bushings. Info on turcite is here. Boedeker Plastics : Turcite A, Turcite X Datashee Boedeker Plastics : Turcite A, Turcite X Datasheet
    I bumped up the length of the bushing to .750 vs the standard .625. Reasoning? Best I could figure the IGUS bushings are a little harder, so I wanted to spread some of the stress out further.




    I'm about 6 rides in to the new setup. Rain and heavy mud included. Everything seems to be working fine, and the bike feels new again. I'm still very much in to the bike, its got clean lines, and as an engineer I can appreciate the simplicity and strength of Banshee's frames.

  2. #2
    FM
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    Nicely done

  3. #3
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    Very cool!

  4. #4
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    I'm sorry that your second hand frame developed issues, but I admire your high quality self manufactured solution. I'll be interested to hear updates about this frame in 6 months time to see how your bushings and shims have lasted. Keep up the good work!

    (Damn nice lathe work, 0.17mm shim thickness is increadibly impressive to achieve without deformation!)
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  5. #5
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    Thanks Builttoride, and the rest, I'll update in the Spring. Winter is coming here

    Quote Originally Posted by builttoride View Post
    Damn nice lathe work, 0.17mm shim thickness is increadibly impressive to achieve without deformation!
    Sharp tools, a well kept 1961 Hardinge HLV, and a couple tries.

  6. #6
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    Wow, good stuff, always cool to see when someone with actual knowledge and access to proper machines has a bike related issue and how they solve it. What sort of time frame are we talking doing all this? I'm assuming it was quite time consuming and not something you'd want to do again.
    One day your life will flash before your eyes, will it be worth watching??
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  7. #7
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    something like this takes a skilled craftsman probably a couple of hours... probably to long for reasonably offering this repair to other people...

  8. #8
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    Quote Originally Posted by LyNx View Post
    What sort of time frame are we talking doing all this? I'm assuming it was quite time consuming and not something you'd want to do again.
    Probably looking at two hours total, but I also machined the thick aluminum bushings for the RP23 and custom cut some DU bushings out of larger stock in that time. The shapes of the bushings are not complicated at all, just very precise, like +/- .0003.


    Quote Originally Posted by MalcolmX View Post
    something like this takes a skilled craftsman probably a couple of hours... probably to long for reasonably offering this repair to other people...
    You are correct, for a guy like me, it wouldn't make much sense to sell this as a service as the price would be unreasonably high. However, if you had a similar issue, and were out of warranty and out of options with getting your frame fixed, you could always bring your frame to a general machine shop and have them make you bushings. A good shop is going to cost you 50-75 bucks an hour, but they are going to want "prints" (line drawings of the part with tolerances), which are usually drawn by an engineer.

  9. #9
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    Quote Originally Posted by blast_off View Post
    This was causing the axle to wobble around and wear things out. I thought about machining a new link (which I may still do)
    Nice work! I am also an engineer with shop access (although our lathes at work are not very good) and have been debating between a similar fix for my frame or just getting a new frame via the upgrade program. The most significant wear for me is on my short lower link at the main pivot. I would like to machine a new one that changes the way the pivot axle attaches to it, but it is not a simple part to make and would not be cost effective to have made. So your solution of the custom bushings and shims is a good balance of not too difficult or expensive to make. Hopefully the bushings last a while since if you need to replace them you will have to make more.

  10. #10
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    Quote Originally Posted by LyNx View Post
    Wow, good stuff, always cool to see when someone with actual knowledge and access to proper machines has a bike related issue and how they solve it.
    Amen. Very interesting post, thanks for sharing it!

  11. #11
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    blast_off, I'm very interested to know what is happened next with your update. Does it work good and you have had no issues anymore?

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