Aprilia RS 125 Selector Drum Rebuild (Rotax 122)



  • I went to rebuild the engine for my Aprilia this weekend, when I thought I would just have a quick look at the selector drum (better safe than sorry). Disappointed then, when I spun the selector drum on my fingers to hear that audible worn bearing sound....

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    I am posting this, because after 20 minutes of not getting anywhere, and after 20 more minutes of searching the internet, and a further 2 hours, I finally retrieved the final bearing from the selector drum. IIRC the DTR Selector drums are similar, so it seems fit to post it here and allow the information to be found.

    The selector drum (as pictured above) is the cylinder that rotates around its axis moving the dog ears up and down depending on the gear you wish to select. In turn this shifts the transmission cogs into and out of position changing the ratios allowing you to increase or decrease maximum velocity.

    There are two bearings you need to replace. Bearing two is 6001. A widely used bearing and can be had for a couple of quid from www.simplybearings.co.uk (I'd recommend getting high quality Koyo bearings).

    The second bearing was widely available, but vastly more expensive. This bearing is 61804. AJSutton helpfully listed these bearing titles allowing me to source Japanese bearings at a much more reasonable price.

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    The bearings should be punched out with a drift and hammer. Bearing labeled 4 is very easy to remove, although is the move expensive one of the two.

    Bearing labeled 2, again is very easy to remove, and costs less than £2. HOWEVER removing the circlip, labeled 3, is a completely different story, and is the reason why I am writing this blog.

    The circlip is a blind circlip, with no obvious way to reach it. There are no holes, it would almost seem that these bearings are not serviceable. After much time I was able to remove this circlip allowing the bearing to be removed.

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    To make access a little easier, and to remove pressure on the circlip, I punched out the race of the bearing, then knocked out the inner bearing (this didn't make the actually removal of the bearing hard since it's not a press fit, merely retained by the circlip.

    Two people are required for the last bit.

    First use a punch to carve out an anchorage point in the ends of the circlip. Then using a nice long flat blade screwdriver, you should be able to twist the driver, forcing your way into the anchorage point. The aim is to move the circlip slightly away from the wall. Then using a fine smaller screw driver (and a helping hand) jab the screw driver into gap you made.

    Once you have the screw driver in between the walls of the drum and the circlip, you should be able to leverage the circlip out. This took us a good number of attempts, we almost gave up on the idea when we noticed the circlip jump.

    The key to our success was using a long enough (sharp) flatblade, so that the other person can easily jab the circlip into the position. Once we had a long enough screw driver, we actually accomplished the task in a matter of minutes.

    We practiced lots and eventually got the technique. I'm writing this so that people who are in a similar position can see that the bearings can be removed without destructively damaging the drum, the item is serviceable if you try hard enough.

    I am going to replace the circlip with one with internal eyes, hopefully simplifying the process in the future.

    Good luck to whomever needs this!



  • You've read my book then.😁



  • @oldman So you're Susan Bauer? Nice to meet you.



  • It's a biography😉



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