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Commando clutch drag 750 v 850

Submitted by richard_potter on Mon, 06/02/2023
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Commando

Since buying my '72 750 Roadster I have always found it very difficult to select first gear with the engine running.  Reading various forum postings I assume the issue is one of clutch drag.  With the engine stopped if I pull in the clutch it takes about 6kg of force to operate the kick start lever.  If I do that same on my '74 850 then the force required is almost negligible.  Changing the four friction plates on the 750 made no discernible difference. 

I know the 750 uses fibre plates as against segmented sintered plates on the 850 so does this likely account for the difference in kick starter force or is it more likely I have some, as yet, unidentified issue with the clutch on my 750?

Regards to all and thank you for reading.

Richard P.

 

 

 

 

Submitted by steve_constable on Tue, 07/02/2023

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My 750 had a similar problem when I bought it. After starting, the engine would stall when first gear was engaged (with the clutch pulled in). I found a very oily clutch when I took mine apart. Replaced the fibre plates and cleaned the steel ones and all was ok.  Perceived wisdom seems to suggest that if you fill to the primary case oil hole there is too much oil in the chaincase. I only put 175cc of oil in mine. I also fitted one of the clutch rod seals from Norvil to stop the possibility of gearbox oil entering the clutch.

I am not sure why the 750 kickstart should require more force. First thoughts are oil in the crankcase or higher compression on the 750?

Submitted by dave_taylor on Tue, 07/02/2023

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Gearbox oil can seep down the clutch pushrod drilling, and, or you've got a buckled clutch plate.

RGM, AN and others sell a seal to fix the seepage.

Submitted by richard_potter on Tue, 07/02/2023

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For your replies. I spent the afternoon taking the clutch apart again (all the plates are clean) and tried replacing one of the driven steel plates with a thinner one - made little difference to the clutch drag but did increase the heaviness of the clutch lever.  I did notice that there is quite a lot of movement in the clutch basket when the clutch is operated.  The clutch had been adjusted per the book but I then adjusted the cable adjuster to remove all the free play at the clutch lever.  That seemed to do the trick - with the lever now pulled fully back there is very little drag when I operate the kick starter.  I guess it is possible then that the bearing that supports the clutch is sufficiently worn that the first few mm of lever movement does nothing but pull the basket over such that the diaphragm spring is not fully disengaged when the cable adjuster is set per the book.

If the weather is a bit warmer tomorrow I’ll do a test ride and see how the clutch operation feels and whether or not selecting neutral is any easier……

Submitted by stan_thomas on Tue, 07/02/2023

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There's also that circlip on the mainshaft behind the clutch that can deform so that the clutch is no longer located properly. The mainshaft nut will be loose in this case.

Submitted by richard_potter on Wed, 08/02/2023

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Thanks Stan.  I took the clutch apart this morning and checked the tightness of the main shaft nut. Sadly (?) the torque setting was correct so it does look like excess play in the clutch bearing is the issue.   I ran the bike this morning and I can indeed now select neutral so I think I’ll run the bike as is for the time being.

Regards to all

 


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