Author Topic: S6 Dragging Clutch  (Read 405 times)

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Offline PaulW

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S6 Dragging Clutch
« on: 15 Mar 2019 at 23:34 »
I've recently bought a 1930 S6 together with quite a lot of used spares.  The bike hasn't been used for 10 years, but having dropped the old oil, cleaned all the gauze filters and oil pump, cleaned up the magneto, changed the tyres etc etc, she is now up-and-running and sounds nice.

But what I haven't been able to do is stop the clutch from dragging.  I cannot select a gear while the engine is running and back wheel is not turning...without a crunching of the gears.  If the back wheel is turning (i.e. on the centre stand), there is no problem at all.  I've had the flywheel off half a dozen times, and have cleaned and checked the two rows of rollers and ball bearings.  I've also checked for a nice sliding fit of the bearing shell onto the flywheel central hub.  I've tried several different clutch plates.  I've also checked the clutch cable length, the clutch arm angle, and the three roller plate that the arm rises on.  The thrust ball race seems fine and I seem to have all the correct thrust washers etc.

Without the engine running, if I pull in the clutch lever, then I can freely kick the kickstarter i.e. clutch is disengaged.  I've not messed with the 4 speed box, but have topped it up with fresh oil / grease mixture; all gears are easily select when rotating back wheel.  When I replaced the flywheel, I lubricated the clutch bearing etc via the central grease nipple.  Could my grease be too thick?

I'm not sure what I'm over looking, so any help and/or advise would be gratefully received.

Paul
Dorset

Offline Eric S

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Re: S6 Dragging Clutch
« Reply #1 on: 16 Mar 2019 at 07:31 »
My bike is a 1937 600 aero and had the same problem with the difference that the rear wheel was always turning at neutral and engine at idle.
After a lot of investigation I noticed that the flywheel/shaft cone surface was getting worst and worst and that the shaft coming out of the engine was loose. Cone bas been rebuilt and hope to be able to put engine back together in the next couple of weeks...

Offline douglas1947

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Re: S6 Dragging Clutch
« Reply #2 on: 16 Mar 2019 at 18:37 »
Paul,
have you checked the clutch cam / lever for using the complete way to disengage the clutch?
The 3 rollers for the cam use to wear.
Is your clutch plate / friction plate really straight?

Michael

Offline PaulW

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Re: S6 Dragging Clutch
« Reply #3 on: 16 Mar 2019 at 21:56 »
Thanks Michael and Eric.

I think I have found the problem.  As I had access to a 1930 T6, I compared the two flywheels / clutches; T6 is on the left and S6 on the right:



Everything looked identical until I examined the flywheel-side thrust race.  On my S6 version, there is step which protrudes into the roller area.  This step is deep enough to foul the rollers when the clutch is operated and also prevents the race sitting on the sprocket.  On the T6 version, the underside of the race is perfectly flat.

S6:



T6:



Having tried the flat T6 thrust race, everything is now working fine and I can select gears without crunching them.  But now I have two additional question:

1) Any idea what this stepped thrust race comes from?
2) Any idea where I can obtain another good non-stepped flywheel-side thrust race?

Many thanks for your help

Paul

Offline PaulW

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Re: S6 Dragging Clutch
« Reply #4 on: 24 Mar 2019 at 08:55 »
An update...and a big thank you to Doug for some great advice!

My flywheel side race above, the one with the step/lip, is actually a push-out one from the throw out cam; it also has a large crack across it.  As I was short of one flywheel side race, and having read on this Forum about the success of converting the ball bearing trust race to a scintered (Oilite) bronze one, I bought the parts and set to work.

Sourcing the parts was surprisingly easy.  The Oilite washer is a Bowman one (part number AW 32 48 04) and was supplied by BearingBoys in the UK, and as I wanted this washer to run against hardened, steel surfaces, I bought 1mm thick and 4.75mm thick needle roller bearing raceways from SimplyBearings also in the UK --- I wasn't sure how many of these 1mm raceways I'd need, but at 4/each, I bough a few spares....





The Oilite washer only needed to have its I/D opened up, so there was no issue with closing up the pores on the bearing surfaces.  For the 1.mm raceways, the OD needed to be reduced which I just managed to do on my rather ancient Sheldon lathe --- fast chuck speed, no cutting fluid and carbide indexed tool:





And so to the throw out cam.  I could have left the Oilite washer running against the old roller race but as I had a throw out cam with a removable race, I decided to do the job right and make a new flat bearing surface from my 4.5mm thick hardened needle roller raceway.  This entailed cutting a 2.75mm step in this washer for the interference fit into the throw out cam. i.e it would leave a 1.75mm thick surface on the top of the throw out cam.  Cutting 2.75mm doesn't sound much but it took several hours and multiple carbide tips to get through this hardened raceway --- with quite spectacular sparks and molten swarf, so wear eye protection!





And this is what I've finished up with. I needed 2mm (2 x 1mm washers) on the flywheel side to ensure the top of my 1/4" thick Oilite washer cleared the main bearing hub.  I could have ordered a thicker Oilite washer but that would have been a "special order" and I just wanted to get on with it... :roll:  Having installed the clutch several times to check clearances / adjustments etc, that helped me decide on the finally thickness (1.75mm) of the new raceway in the throw out cam.



So, it works on the bench, but will it work when the engine is running?  Time will tell as I'm not quite ready to attempt an engine starts...

Thanks for all your advice Doug!