Author Topic: S6 - Clutch slip - ethanol  (Read 3820 times)

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Offline Michael Scott

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S6 - Clutch slip - ethanol
« on: 03 Oct 2011 at 10:05 »
With lots of help I got my S6 box of incomplete bits on the road a couple of years ago and had lots of fun but with some clutch slip which I had to ride round.  When I rebuilt the clutch I had the maximum sized disc of ferodo bonded to the clutch plate and used new clutch springs from the Club. After the Banbury run I took the clutch to bits and made some minor clearance changes but more importantly I took note of the witness marks and took a 4 thou skim off the ferodo (face mask and hoover the lath afterwards !).  I also took Frank Dolman's advice and reassembled with only three clutch springs (I know that is counter intuitive - less pressure force more slip). The result is acceptable clutch lever force and I can accelerate up through the gears from a virtual standing start on a nearby reasonably demanding hill without a hint of clutch slip (I will probably regret putting that in writing but euphoria reigns!)

Ethanol
With beautiful weather and quite a lot of short rides my ethanol problems have increased (I already had a tank problem). I noticed that the throttle was stiff and then that there was a lazy return so started to inspect the throttle and the cable but they were fine. The problem was a sticky desposit between the throttle slide and the carb body. Now it seems to me that this is caused by the heat from the exhaust evaporating the petrol left in the carb when I stop (like reducing a sauce in cooking) and inevitably it is the heavy ends of the petrol that are left and they accumulate until partial seizure results. A natural outcome of the S6 carb exhaust pipe configuration.
Has anyone else suffered this problem and is there a solution?
Michael

Offline Doug

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Re: S6 - Clutch slip - ethanol
« Reply #1 on: 03 Oct 2011 at 16:23 »
Michael,

Regards ethanol. I have not had a problem per-say with the fuel (10% ethanol) evaporating and leaving a deposit, but the fuel dissolving other things and leaving the deposits behind in the carb. In my case it was the tank sealer being dissolved and then transported to the carb slides. This glued them shut over the winter such heat was required to get them unstuck. Acetone cleaned everything up and the tank sealer was replaced by a more recent product that seams to dissolve more slowly; though I have yet to find any sealer that is ethanol proof.

If you do not have tank sealer in the system, check to see if the lining of your petrol flex is not getting soft and gooey.

-Doug
P.S. Yes, using less springs in the clutch does sound counter intuitive.

Offline eddie

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Re: S6 - Clutch slip - ethanol
« Reply #2 on: 05 Oct 2011 at 08:28 »
Michael,
               I am also surprised that you get away with less springs in your S6 clutch - especially as you are using a 'Ferodo' type lining. On the postwar models, Douglas used Ferodo but reverted to cork linings for the higher powered 'Plus' models to prevent clutch slip. Also, the original S6 clutch plate only has the corks protruding about 40 thou, so I wouldn't have thought there was enough room for a 'Ferodo' lining without reducing the thickness of the plate. If this has not been done, then maybe it has affected the operating geometry of the clutch release.
      On the subject of the ethanol - we are all suffering from the effects of the modern brew that masquerades as petrol. If left in a carburettor to evaporate, it usually leaves a sticky residue that either blocks or severely restricts any jets, and causes slides to stick. This problem can be exaggerated on machines like the S6 due to the close proximity of both the hot exhaust and timing chest increasing the evaporation rate - the S6 is a big old lump that takes ages to cool! Whatever machine I am using, I make a point of turning off the fuel and leaving the engine running until it empties the carb before putting the bike away - this seems to have got over that problem.

          Regards,
                          Eddie.

Offline Michael Scott

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Re: S6 - Clutch slip - ethanol
« Reply #3 on: 05 Oct 2011 at 09:00 »
Eddie
Thanks for that.  Yes I did change the geometry of the clutch and had to do some minor machining which I had to do anyway because the clutch was in a rather sad state when i got it. Give some earlier sad S6 Clutch stories on this Forum I thought that a radical approach was needed.

I have now adopted the run to empty procedure but will not know the result until next year now since I suspect S6 riding will diminsh sharply this year. (Tank has already been drained!)
Regards
Michael