Clutch Drag

[Woody850]

I must apologise for opening once again a clutch drag thread. Much time has been spent reading articles and threads but nowhere could I find the answer.

I rebuilt the clutch on my 73 850 with a new centre bearing, pushrod, circlips and rear circlip. The plates got a good cleaning and a pushrod seal has been present for several years now.
Last year I had the the centre adjuster screw backed of by about ¼ of a turn although the lever adjuster is fully screwed out leaving little or no play (not optimal I know). With this setting I could ride the bike without drag and go through the gears and select neutral normally.

This year I first tried backing the centre screw off ½ turn but at the handlebar lever I had to screw the adjuster out as far as it would go. Back home I reverted to backing off the centre screw ¼ turn but found the result to be the same, lousy tickover, hard to select gears and inability to find neutral.

Helpful information would very gratefully accepted.

 

[Peavey Jeltz]

Did you check the plates for flatness on a glass plate or similar while you had them out for cleaning?

 

[lazyeye6]

Two thoughts:
Tight primary and/or drive chain
Notched clutch center and/or chainwheel

 

[Woody850]

Did you check the plates for flatness on a glass plate or similar while you had them out for cleaning?

That comes as a though, I lay them as a pack together and they sat on each other snugly. I have just been at it again and pulled the pushrod and thought I smelt GB oil on the adjuster face.
Tried many settings but couldn't stop the kickstarter turning the rear wheel while in first gear.

Both chains have enough play while the clutch basket is in good condition.

When I fill the GB I shine a light on the overflow plug and fill to below the plug, bike on centre stand.

 

[cash]

Tried many settings but couldn't stop the kickstarter turning the rear wheel while in first gear.

I think that's normal.
After you rebuilt the clutch does it still drag? If so it has to be one or more of; buckled plate, tight primary chain, wear or slack in the main shaft/clutch assembly allowing the whole clutch to move.

 

[Woody850]

wear or slack in the main shaft/clutch assembly allowing the whole clutch to move

Could you explain that in detail, I did not quite understand where the slack would be.

As soon as I have a bit of time I will strip the clutch again and scrutinise the plates. Is there a possibility of a buckled diaphragm?

 

[L.A.B.]

Tried many settings but couldn't stop the kickstarter turning the rear wheel while in first gear.

As cash said, that's normal because operating the kickstart in 1st gear turns the layshaft.

How much clutch lift at the diaphragm spring (centre)?

 

[gortnipper]

I would first look at the primary chain tension. An easy way to do this without draining and pulling the cover is using a 10mm open end wrench held steady against the edge of the inspection hole for reference to check chain play.

Dont be afraid to make too loose at first, just for troubleshooting to see if it fixes tick over and the finding of neutral. If it does, then you can snug it up appropriately.

 

[Torontonian]

Fit a new clutch cable ?
A new clutch center makes the world a better place to start from.

 

[CanukNortonNut]

Could you explain that in detail, I did not quite understand where the slack would be.

As soon as I have a bit of time I will strip the clutch again and scrutinise the plates. Is there a possibility of a buckled diaphragm?

Using the tool, take the diaphragm off the clutch basket. Now take the tool off the diaphragm and let the diaphragm spring relax to its normal state. Re-install the tool and carefully adjust, only just enough to allow movement in the clutch diaphragm to spin behind the big cir-clip when in the basket. It could be that you pushed the diaphragm over and in too deep causing the clutch to drag. In other words you flicked the diaphragm to the other side of the curve. You will find this phenomena happen when you have severely worn out clutch packs.
Cheers,
Tom

 

[Joachim]

I just went through the same on my 850 MkII. I could only switch into neutral when the bike was rolling and selecting especially first and second gear was hard. The solution finally was replacing the clutch center which had some severe notches, probably up to 1mm deep. This probably stops the plates from moving sideways and disengaging the clutch.

 

[cash]

Could you explain that in detail, I did not quite understand where the slack would be.

As soon as I have a bit of time I will strip the clutch again and scrutinise the plates. Is there a possibility of a buckled diaphragm?

The bearing that's held in place by the clutch operation mechanism is worn, or the nut underneath it holding the mainshaft in place could be slack. Before you start taking it apart watch the basket and slowly operate the clutch lever. If the basket moves out a little before the diaphragm that's a good sign that could be the problem. The basket movement can also be caused by a slack clutch nut but you said yours is tight. I don't think a buckled diaphragm would cause drag, but you never know, worth a check.
Dave

 

[concours]

That comes as a though, I lay them as a pack together and they sat on each other snugly. I have just been at it again and pulled the pushrod and thought I smelt GB oil on the adjuster face.
Tried many settings but couldn't stop the kickstarter turning the rear wheel while in first gear.

Both chains have enough play while the clutch basket is in good condition.

When I fill the GB I shine a light on the overflow plug and fill to below the plug, bike on centre stand.

Read dynodave’s clutch information.
Do it once & enjoy a well behaved clutch. Pushrod seal too.

dynodave Atlantic Green Technical Services

 

[Woody850]

How much clutch lift at the diaphragm spring (centre)?

Just made the measurements and have after several attempts come up with a deflection between 2.4 and 2.1 mm and just to note as a reference I used the recess of the inspection plug which gave me 31 mm to the boss of the diaphragm while released.

 

[Woody850]

With the clutch stripped and the plates cleaned up I checked that they were even on a piece of glass, all was fine. I took the measurements and list them below:
Copper plates 3.1 mm
Steel plates 2.3 mm
Stack height without thick steel plate 24.0 mm
Stack height with steel plate 27.8 mm

No notches to be found on the centre splines and I have a new clutch cable fitted.
In the workshop manual they have 4 fibre and 5 metal plates which must be wrong and friction (fibre plate) should be between 3.759/3.607 mm
Is this true?
Any answers to this?

 

[L.A.B.]

In the workshop manual they have 4 fibre and 5 metal plates which must be wrong and friction (fibre plate) should be between 3.759/3.607 mm
Is this true?

That's 750 models (late 750 models also had the 5 bronze friction plate and thin pressure plate clutch).

dynodave Clutch Pack for Norton Commando - Atlantic Green Technical Services - British Motorcycles

 

[Woody850]

Thanks LAB I just did some calculating or rather converting and my clutch seems to be in the parameters. I will loosen the primary chain and put it all together but I really am stumped.

 

[L.A.B.]

Just made the measurements and have after several attempts come up with a deflection between 2.4 and 2.1 mm

That seems a bit on the low side to me.

 

[Woody850]

That seems a bit on the low side to me.

Would you suggest I look on the gearbox side after it is together and as a question what should I expect for movement?

Could the clutch rod seal screwed onto the end of the mainshaft be of disturbance?

Sorry that I am picking your brains but it's a great help.

 

[L.A.B.]

Would you suggest I look on the gearbox side after it is together

Yes, it could be worth checking.

and as a question what should I expect for movement?

My Mk3 I get about 3.2mm/0.126".

As the thrust ring of the pressure plate is at (about) the mid-point of the diaphragm spring and although I don't have any figures I would estimate the actual 'clutch lift' to be significantly less than the 'pushrod/centre' lift.

Could the clutch rod seal screwed onto the end of the mainshaft be of disturbance?

It's a possibility and would be worth checking.

Sorry that I am picking your brains but it's a great help.

Always happy to help if I can.