Not all shift drums are the same!

[Bill Campbell]

Tried to put my 79 125 bottom end together tonite with the help of our mate Dennis. Guess what when you tighten the engine allen bolts up the shift drum locks solid. Back the bolt off half a turn and the drum would work. We compared it with another Den had and there is about 1.5mm difference in length. I can only guess that somewhere the bottom end I bought had a strange drum put in it as I bought the motor locked up with corrosion. Does anybody know the history of shift drums from say 1974 to 1980? We learn't another new one tonight.

Cheers Bill

[Kip Kern]

I can say from the 100's of engines I have torn down 71-76, I have noticed no difference in length of the drums.  Of course the 71/72 and some 73 KTM's have the old fashioned drum VS the new drum on the later 73 and up. Good thing to have a few used around to make comparisons.  I never messed with anything later than 78 so there may be a change of some sort.

[G Ellis]

Bill ... Take the shim off of the shifted drum. I have to do this because the center gasket are not the right thickness.  Or the bolt on top of your shifted drum-clutch activator is to long. Hope this will help.

[Bill Campbell]

Heres where I am at. It is possible it is a shift drum from a 1981 125. Cannot confirm it at the moment and how it got into a 1979 125 is another story altogether. What I have is two first generation shift drums that measure 125.84 and 125.96 mm bearing surface to bearing surface ie inside of case to inside of case. The drum that was inside the 1979 cases measures 127.92mm and the distancse inside the case including gasket mrasures 127.78mm. You can see that it just binds but my quandry is where should the shift drum sit in relation to the sides of the cases and can I have almost 2mm side play if I used one of the first generation shift drums. I do not know what tolerances there are before the shift forks are in danger of being bent. Thanks guys for the other suggestions.  Bill