Clutch coming off crankshaft taper

Forums Technical Two Stroke: Help needed Clutch coming off crankshaft taper

  • This topic has 7 replies, 4 voices, and was last updated 6 years ago by Anonymous.
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    • #7340
      Anonymous
      Inactive

      I have a 250/1 I cannot keep the clutch on the crankshaft taper. Ive changed the housing (second hand) but it still comes undone when running. The shaft and housing have been properly degreased after (gentle lapping) before fitting and tightened as per the manual and it stays on the taper as described. I used the clutch bearing for the pretightening before final assembly. What am I doing wrong? or do I need a brand new clutch assembly?

    • #7341
      Richard Smith
      Participant

      Try putting some washers on the shaft as well as the bearing,to make sure the clutch is fully home.It needs to be very tight .If it still comes off when running,then the crankshaft may have been damaged when it spun off.
      A member of my section, [Yorkshire] had a keyway machined in his crankshaft,to prevent the clutch coming loose,but the cost was not far short of buying a new crank.Don’t know about the 250/1,but a new crank for my ETZ 300 was 90 euros from Ost2Rad,[currently,101 euros],it has now covered 12000 miles without any trouble.

    • #7342
      Richard Smith
      Participant

      Just had another thought.There is a very thick washer that goes on the end of the crankshaft,have you put it on?

    • #7343
      Anonymous
      Inactive

      Thanks for the reply.

      When I bought the bike the engine was siezed and the clutch was removed with the washer missing. After bebuilding the engine with a new crankshaft I made a washer to suit and followed the instructions but it would not stay on the taper. I eventually realisded that it was bottoming out on the inner thrust and wavey washer. As an experiment I machined a few thou off the inner face and it seated fine and lasted for a few hundred miles.
      I bought a second hand clutch inner, swapped the clutch bits and it worked ok even lapping it gently as reccomended. However this one only lasted for a few miles before it came loose and the resultant push home. The bore of both inners always looked slightly ragged and were not smooth so suspect that the replacement may have also been faulty.

      Good to hear yours has lasted, if someone had a keyway cut do some engines suffer from this problem? A new clutch inner is sounding very attractive!

    • #7344
      Richard Smith
      Participant

      Talking MZs at various rallies,I have heard of two cases of the clutch drum coming loose.One from the bloke it happened to,the other from someone who knew someone.It seems to be fairly rare,and my guess is its cause is incorrect assembly and/or inadequate tightening.
      A new clutch inner should solve it,I think it is the pressure plate that you need,the tapered inner is part of it if memory serves,[its been about two years since I last stripped my clutch].Both the MZ shop and Ost2Rad have them at £46 and 40 euros.
      Best of luck with it.

    • #7345
      Membership Man
      Moderator

      I suggest before buying a new clutch centre that you double check the state of the taper on the crankshaft as well. This should be smooth and there should be a number of horizontal grooves (4 I think) running down the taper. If these are no longer present or in any way worn then the crank has suffered as well. You may find you can still get round this with a new clutch centre and by using a smidgeon of bearing fit to hold it in place. But be warned that if it works it will be the devil to get off again probably needing heat to softer the adhesive.

      By the way fitting a key into the crankshaft is neither necessary nor desirable. The taper is what provides the grip. A keyway is primarily to provide a positive location for things which need to be lined up correctly e.g. the dynamo stator to ensure timing is correct. Keys don’t provide a secure drive except perhaps in very low stress applications and on an MZ with a worn taper would almost certainly fail quite quickly doing even more damage. Not a good investment for this application.

      PeterF

    • #7394
      Anonymous
      Inactive

      Thanks for the replies, it looks like I’ve got a problem rather than just incorrect assembly as I’d never done before. I’ll check the crankshaft for damage but I’m going to renew the clutch centre and go from there.

    • #7411
      Anonymous
      Inactive

      Interestingly enough in the ‘official’ manual it advices you to check the tightness of the clutch nut every time any service work is carried out so this must have been a known problem but by regular checking it’s torque this is overcome.
      Mick
      es250/1
      ts250/1

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