Saturday, March 8, 2014

2013 KTM 50SX - Clutch Replacement.

Clutch slipping, loss of drive but, more importantly, no race wins!
Moving on from the centrifugal, three shoe clutch of the previous mini KTM's, they now have an adjustable, multi-plate assembly fitted. Let's have a look inside.

First thing to remove is the brake pedal so the clutch cover can be removed. The cover itself is fitted with a large O-ring so no gaskets to worry about.

Four bolts and it's off. The three holes in the clutch basket allow access to the clutch adjusters (allows you to alter the point, or revs, at which the clutch starts to drive). The Torx bolt in the middle really needs an impact/air gun to remove it. Using a pair of thick gloves makes it easier to hold the clutch basket while you undo it.

Bolt out. Don't lose the washer!

With basket lifted out of the way, you can see the clutch mechanism. Take off the thrust washer in the middle and remember to refit it afterwards. The three hex bolts are the adjusters. The six Allen bolts hold the clutch together.

There's always one bolt that doesn't want to move! The Allen key started to twist in the hexagon so a light tapping with a ball pein hammer was needed to make it tight again. Eventually it yielded.

And there's the clutch pack. The plates just slip off, and the complete kit from KTM just slips straight back on. Easy... read on.

I wanted to look a bit more at how the mechanism works. Six springs, three of them adjustable. Six pairs of ball bearings which ride up their respective ramps when the engine is turning fast enough - it's still centrifugal. As they ride up and outwards, they pull the back of the clutch assembly which compresses the springs and engages the clutch. Sorted.

OOPS! Started to fit the new plates and then realised the larger cutouts are for the springs, while the smaller ones should go around the posts. It should also be noted the first and last plates only have friction material on one side.

The old clutch pack. Measured altogether with a digital vernier at 14.6mm thick. The new one measured at 15.3mm.

Fitted properly. The plates are a good tight fit around the posts. The springs are a bit fiddly to get in the right spot but, with a screwdriver and a little jiggling, the cover goes back on. Try to keep the tabs on the plain plates all inline so the clutch basket can go on easily later.

Spot on!

At this point the top cover can be bolted back on with a little dab of Loctite on each of the bolts.

Then slide it back on to the bearing and refit the thrust washer. The clutch basket can now be slid over the clutch pack and the bolt and washer can be refitted.

A small dab of Loctite went on the centre bolt too.

And finally the adjustments. They click just like a suspension adjuster. We put it back to factory settings and all that was left was the cover and brake pedal. Simple enough. 

Happy to say it worked a treat. The bike takes off nicely now, and almost flipped the first time Billy gave it a handful! Race wins coming up.
You can buy aftermarket covers with inspection holes which allow you to adjust the clutch without removing the entire thing... good idea. Apparently, these clutch packs can be retrofitted to the older versions with three-shoe clutch too.