Clutch Failure on the Track!

[unicorn_violence]

Hello Everyone.
i've never dealt with a motorcycle clutch before, so i thought i would pick some brains here before taking things apart.

i started feeling looser play in the clutch while at the track yesterday, and it kept getting worse. it basically felt like there was less and less resistance in the clutch lever. right at the end of the day, i lost all resistance, and the clutch stopped working. granted, i could still hard shift gears up and down without the use of the clutch. i did not heard any banging sounds inside the clutch either while shifting (thank goodness). my instant thought was that the cable snapped. however, i could see that the cable was pulling the lever that sits on top of the clutch, so that was eliminated as a possible cause.

anyone else have ideas as to what might have happened?

 

[motoputz]

if you still have drive to the rear wheel it is not the clutch pack. The cable sheath adjustment is probably loose at the lever. Or you did break some of the strands of the clutch cable and it is stretching. You can see movement on the lever arm on the outside of the case but it might not be moving far enough to disengage the clutch. The other possibility is that whatever is attached to the other end of the rod passing through the case that acts on the clutch rod has come adrift. I have not had mine apart in that area so I can not give you an idea of what could go wrong in there.

 

[green_bread]

The nut that holds the basket on has backed off. Same thing happened to me in a race last year. It's reverse threaded and kind of a bitch to properly torque at the track with limited tools.

 

[unicorn_violence]

The nut that holds the basket on has backed off. Same thing happened to me in a race last year. It's reverse threaded and kind of a bitch to properly torque at the track with limited tools.

that sounds about right Green Bread. that would explain why the resistance lowered steadily throughout the day. the lever above the clutch was definitely moving in in its full range, so i don't think the lever cable stretched at all. we shall see what happens when open up the bike sometime this week.

 

[Diploman]

I concur with Green Bread's diagnosis. Backing off of the inner clutch basket nut was a frequent problem encountered when the 390's were introduced in 2013. KTM addressed this issue by upping the torque spec on the nut. This change cured the nut loosening problem to a major degree, but it still happens occasionally, and Unicorn's issue appears one of those isolated instances. The Repair Manual now states that the inner clutch basket nut is to be torqued to 120 NM (88.5 ft/lbs) and secured with Locktite 243. The nut is a left-hand thread.

 

[unicorn_violence]

So Green Breads diagnoses was correct, that nut had back out inside the clutch basket. im gonna try and put everything back together tonight. does anyone know the torque specs of the bolts that squeeze the clutch pack together?
below is the bolt that backed out for future reference.

 

[green_bread]

Thats the one that got me. Were you lucky enough to get out without stripping the threads on the nut/shaft?

I cant remember the torque we used on the 5 bolts for the clutch pack. I dont think its a super high torque spec from what I remember, though.

 

[unicorn_violence]

Thats the one that got me. Were you lucky enough to get out without stripping the threads on the nut/shaft?

I cant remember the torque we used on the 5 bolts for the clutch pack. I dont think its a super high torque spec from what I remember, though.

yes i did. it looks like the bolt just vibrated itself loose and backed out. the threads are all there. dang thumper engines and their vibrations!

got some blue locktite, so hopefully that does the trick and this doesn't happen again. that definitely would have been a pain if it happened during a race weekend.

 

[green_bread]

yes i did. it looks like the bolt just vibrated itself loose and backed out. the threads are all there. dang thumper engines and their vibrations!

got some blue locktite, so hopefully that does the trick and this doesn't happen again. that definitely would have been a pain if it happened during a race weekend.

Thats exactly what I did. Didnt have any issues with it for the rest of the year, last year.

Really, it was just a pain during the race weekend because I didnt have access to the tools to make the job easier. It was all done with an electric impact and trying my best to hold the clutch basket by hand. I think we finally figured out that you can wedge something between the teeth but thats still not an ideal solution. Haha!

 

[oroone]

The nut that holds the basket on has backed off. Same thing happened to me in a race last year. It's reverse threaded and kind of a bitch to properly torque at the track with limited tools.

What tool do you need to properly screw it back? do you need to take out the entire clutch or just the top plate? thanks in advance!