General => Douglas Motorcycles - General Discussion => Topic started by: Stuart Lister on 25 May 2005 at 07:07

Title: Flywheel clutch self-dismantles
Post by: Stuart Lister on 25 May 2005 at 07:07
Hello group,

The rebuild of my EW is nearing the final stage, and I have come up against a problem I didn't expect.  Whenever I try to start the engine, the clutch falls apart.

What seems to be happening is that the engine itself is quite stiff after it's rebuild. The cylinders have been bored to a tight fit to the cast iron pistons, and, until it is run in, it is stiff to turn over. If  I give it a good old swing on the kick start, instead of the energy being transfered through the clutch to the engine, all that happens is that the flywheel turns, but the clutch spring adjusting nut doesn't, and the whole clutch assembly just dismantles itself before my very eyes. I don't think I have missed any parts off, and the drawings in the book don't seem to show any way of locking the nut to the shaft. I don't want to use locktight, because I will have no clutch adjustment if I do.

I have no previous experience of a clutch like this, so I wouldn't be at all surprised if I have done something daft, or overlooked something that should be obvious.

Does anyone have any suggestions?

Thank you,

Title: Flywheel clutch self-dismantles
Post by: Doug on 06 Jun 2005 at 02:53

If the flywheel turns over but the engine does not, then the flywheel is spinning on the crankshaft taper; problem number one.  But the clutch adjusting nut NOT turning with it is baffling.  It would make more sense if the clutch adjusting nut turned, but the flywheel nut that it threads in and out on to did not.  Then the clutch adjusting nut would un-thread off the end of the flywheel nut, and drop off.  I would think the clutch would start to slip before it got to that extreme.  

Alternately the clutch adjusting nut AND the flywheel nut could turn with the flywheel, then the whole flywheel would fall off the crankshaft taper.  

But if the flywheel turned, and the clutch adjusting nut did not (assuming the crankshaft nut is stationary as the engine is not turning over) then there is no relative motion between the clutch adjusting nut and the crankshaft nut, so it should not un-thread.  The last possible combination, but improbable, all parts of the flywheel clutch turn BUT the clutch adjusting nut.  However even if this were possible, it would cause the clutch adjusting nut to tighten, not loosen.  

Loose flywheels were always the bane of Douglas.  The flywheel needs to be a really good fit on the taper.  If the taper in the flywheel bore or on the crankshaft are torn up, then some remedial machining is required.  Otherwise one proceeds with lapping compound to lap the tapers into a mating fit.  Good enough is when you can wring the flywheel onto the taper dry, then not be able to pull it straight off by hand without giving it a twist to break the fit.  

The next thing to check is if the flywheel nut is tight.  You are not bolting on the cylinder here, flywheel nuts have to be dead tight.  Second, is the nut actually clamping the flywheel into the taper?  If the flywheel sits too deeply on the taper (lapped too many times) the flywheel nut might be bottoming out on the threads before it fully bears upon the flywheel.  Leaving out the thick washer (drive dog, with the two tabs) from under the flywheel nut could also cause the nut to run in beyond its normal position and so run short of threads.  Or this washer itself could be at fault.  Again, if the flywheel is sitting too deeply on the taper, the washer could be abutting the shoulder on the end of the crankshaft.  It can also be installed backwards, but that should be readily apparent.  In all these situations you could have the flywheel nut done up tightly, but it is only just nipping the flywheel onto the taper instead of clamping it on securely.  

I have also once seen a flywheel that had a ridge at the small end of the bore formed by the end of the crankshaft (the flywheel is soft.)  On placing this flywheel on a crankshaft other than the one it had been mated to, the flywheel got hung up on this ridge and behaved as if the two tapers were miss-matched angles.  

Title: Flywheel clutch self-dismantles
Post by: Stuart Lister on 06 Jun 2005 at 08:19
Thanks for that Doug.

You are quite right, it was the flywheel spinning on it's taper. It did fall off eventually and even I spotted it then. The clutch adjusting nut was also turning, and it was this unthreading itself that was the first obvious symptom.

The flywheel seems to fit pretty well on it's taper. I can tap it on, and it won't come off with a straight pull. (I seem to remember, when I was at the dismantling stage, that the flywheel was such a good fit on the taper that I almost had to resort to dynamite to get it off. How can it be this difficult to get it to go back on???)
I have stopped the adjusting nut from unthreading itself by putting a lock nut on behind it. This is not shown in any of the books, and it probably makes adjustment more difficult. but it seems to work.

I have now fixed the problem I had with compression, and fixed (I hope) the flywheel. All I have to do now is figure out why it still won't start. I'll spend some time today checking over the usual suspects, and if it still won't strike up, I'll post another question.