why is the norton atlas clutch such a bear?"

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seattle##gs

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I have worked with 3 Atlases and the clutches have all been very difficult to operate. I have tried all the usual cures but nothing really helps. Why?
I finally used a Magura Hymec system on my own Atlas and it worked very well, however, I have a Triumph clutch so I can't say for sure that the Magura system is the total cure. Any one tried the Magura clutch with the stock Atlas clutch?
 
No, but I had fitted the Cdo diaphragm clutch with the proper mainshaft and belt drive , plus the Atlas hub cover as previously mentionned !
 
IIRC, the Atlas clutch was originally designed for a 500 cc machine. Over time the engine displacement went to 600, 650, and finally 750 cc, resulting in a design that was pushed too far. The plate count was increased to cope with the increased load, then the spring pressure was increased, until it became a bear.

A Teflon lined clutch cable by Venhill can reduced clutch pull by about 25%. This has made my Atlas clutch manageable.

I am not familiar with the Magura Hymec system.

Barnett plates are said to have increased coefficient of friction when oil covered, and with ATF may allow reduced spring pressure without slippage. I have recently installed Barnet plates, and set spring pressure 1/2 turn less than that to make spring nuts flush. So far no slippage, but as I have new rings without enough break in miles, I have not yet put the hammer down.

Slick
 
You do not state why it was difficult to operate, mine was fine with standard clutch lever until I put a pair of racing alloy levers on, then it became difficult. It was traced back to the distance between the centre of the clutch nipple to the centre of the fulcrum pin, which the Norton handbook clearly states should be 7/8 inch-go and check it!!!!


Ditto; the same on the clutch ass. In the gearbox end, I bet you don’t know what you have in there!:)
 
Last edited:
@Bernhard

I have 7/8 inch lever fulcrum centers, and I have stock Norton gearbox actuator. I am the original owner of my Atlas, so I do know what is in there!

The Atlas clutch is a four finger affair .... can not get around that. My first Atlas was the same, and my brother's '65 was no different.

It is simple physics .... for a given plate area, no slippage means adequate clamp pressure .... adequate clamp pressure requires more force to lift off.

Slick
 
I have a set of emgo levers that are 1" or slightly more distance, have had good luck with these reducing lever pressure.
 
!" levers will make the situation worse. You could try re-profiling the gearbox actuating lever ramp. A popular mod.
 
Interesting, whats the theory behind that?.Is the clutch center also modified?. The springs are barely done up. Is that an 88?. It would appear that the plates would bite sequentially ,a bit like a slipper clutch.
 
Last edited:
seattle##gs said:
I just don't see how it improves clutch pull, it is the same three springs either way.
Click to expand...
Simple, when you move away from standstill, the plates tend to "lock up" on one another, the opposite effect happens when you close the throttle/change down as the plate "free off" (You could in theory use weaker clutch springs) -you do not get the back wheel locking up when you change down too early-in effect it acts like a "slipper clutch" there was also the same mod to the Commando clutch.
 
norton bob said:
Interesting, whats the theory behind that?.Is the clutch center also modified?. The springs are barely done up. Is that an 88?. It would appear that the plates would bite sequentially ,a bit like a slipper clutch.
Click to expand...
When under power the clutch servos together and the faster you go the tighter the clutch gets, you back off and it is a 2 finger operation. Originally when Heinz worked at Bracebridge Street he got ahold of some unmachined clutch hubs and cut those to do the servo. He used them on his Dominator race bike. Later when talking to a friend in NM about them they decided to try and machine the basket instead of the hub which worked just as well and is easier to do and find. Not knowing what angle would work best they did it a degree at a time until they got to 19 degrees as optimal. An un machined hub I expect for average people would be difficult to do. This clutch is on an Atlas and no the springs aren't tight because they only have to hold the clutch pack together not force it to hold.
As a side note Heinz wasn't an "engineer" and when he showed the management at Norton his improvement and how well it worked they were only interested in how that would "allow" them to reduce the number of plates and save money. They weren't interested in reducing the clutch pull and rider fatigue. I do miss my friend Heinz.

John in Texas
 
Hi John,I would like to try this, Appart from the 19degree cut, the plate slot in the drum has been widened at the entry, is it possible to get a measurement for this?.
 
IIRC there is a difference between the profile of the Dommi clutch operating lever (in the gearbox) and the Commando clutch operating lever. Years ago I swapped the clutch operating lever on my 650SS for a Commando operating lever and it significantly reduced the effort needed to disengage the clutch. On the other hand the clutch does not fully engage until the handlebar lever is nearly fully released, but that is a phenomena that I have noticed on a number of Dommis over the years.
 


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