HI,
I assume by the "spline part" that you mean the quick thread. The clutch cable pulls to a short lever, attached to a three-start aluminium quick thread, which fits into a matching "quick thread " in the engine case. When you pull on the clutch cable, the lever rises and the quick thread rotates and moves inwards, to lift the clutch pressure plate.
As far as I can see there are only two potential problems here. You don't say which model you have, but the disc-valev engines all use similar systems. Firstly, on the 50/60, 90/100 and 175/200 motors, there is a short 6mm hardened steel roller which fits into the inner end of the clutch lifter and acts like a short pushrod. On the 350 engine, there are two pushrods going through the centre of the gearbox countershaft with a 6mm steel ball between them. If the steel roller or that ball is missing, there will be a lot of play in the clutch mechanism, and you will not be able to adjust this out. Examination of the relevant pages in the parts book should show where the roller or ball fit.
The only other obvious problem is the fact that the quick thread is a 3-start thread. It is therefore possible to fit it in any of three positions, only one of which is correct. If there is loads of play before the lifter contacts the clutch, remove the lifter, turn it through 120 degrees and re-fit it. If this doesn't cure the problem, turn it 120 degrees in the other direction and try again. If there is still no joy, you may have an internal problem.
Hope that helps,
Graham
