Clutch help 250mx 1980

[Adrian Crawford]

Well, with an event only 10 days away we did a bit of service on our KTM team. We got a 80 250 mx but clutch slips, We have free play at the lever on the crankcase, but giving her a run (up the road) clutch slips pretty easy.
This is a similar motor to my 79 (which works) and my 1981 which floods!
Advice appreciated.

[Mickey Sergeant]

Friction plates worn or week pressure plate springs, or combination of both.

[Mike Rosso]

IMO Mickey is spot on.

I know on the later models you could add an additional steel plate and/or put washers over the posts at the base of the springs (spark plug washers worked). If the plates are worn then the spring washers are moot as the pressure plate ends up sitting on the top of the inner hub. If you know the dimensions of the clutch plates new, the quantity, then you can calculate how tall the entire stack should be new. Then if you take the pressure plate and sit it on the top of the inner hub and measure the clearance between the top and bottom friction areas then you'll know what you need minimum and maximum. If the plates are within those two measurements then it's the springs that are the problem.....then go find all of those old spark plugs that you knew you were saving for a reason.

[Adrian Crawford]

Clutch Fixed.
I know there are a few threads on this so will pass on what I have found in case it helps the next man. I might not have this in the logical order so apologies.
(assuming condition of plates are good.) (assuming the clutch springs are in spec.)
1. Measure the thickness of the whole 'pack' of clutch plates/drive discs. I needed to add another drive disc to get to the total pack thickness stated when added up in the parts manual. (x discs +y drive plates.)
2. Although there are dimensions for the actuating rod length I found a prev owner had messed with the pressure plate adjustment screw(if you have one) so the rods were too long. I had to shorten and re harden.
3. Adjust the rod length to ensure you have the correct distance/ dimension from the operating arm to the cranckase. On my 79 this was 42.5-43.5 and on the 1980 with the different mechanism 43.5-44.5.
This arm dimension is critical, too far from the case means the rod does not bear correctly on the actuating assembly and gets pushed up, causing friction, enough that is spins with the motor and quickly ruins the single ball bearing between the two rods. The clutch clearance goes away and your finished and the clutch gets real heavy as the rod gets more and more hung up with ridges.
4. Which I guess should come sooner... I took the operating arm apart, re finished the bearing where it hinges, removed and turned around the hard steel pin where the operating arm sits.
5. So now with the clutch pack thickness correct, the operating arm at the right distance.
6.Then i pulled the lever to the bars and tie wrapped it in position. I adjusted the screws on the pressure plate (springs) to try to get the pressure plate lifting /clearing evenly. I used a dial guage initially, but found that by touching the pressure plate it completely changed the reading, in other words the darn thing seems to bobble about all over the place. I abandoned the dial guage and adjusted the springs to give roughly a thread or two showing (enough for the lockwire) and a relatively even clearance (by eye) as i spun the rear wheel.
7. I checked the clutch operating arm distance from the case once more.
8. Reasembled , filled with atf dextron II and hey presto, working clutch for the whole meet.

The later bike with the better bearing cap for the pressure plate is still important to get the dimension for the arm/crancase right. One bike the clutch plate 'stack' hieght/thickness was completely wrong and I adjusted with some spare drive discs
Get the dimensions of the pack hieght correct (as in the parts book) and the clutch arm to case spot on and you have a chance.
Trouble is whoever fiddled with it before you could have made some errors or bodges.

Ran two bikes this weekend in Cornwaal, the 79 250 and the 80 250. Both worked perfectly for the whole meet. Yeehaa.