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1951 ES2 Clutch worm arc of movement.

Submitted by keith_mountain on Tue, 01/10/2019
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My 1951 ES2 began to suffer from very bad clutch drag. On examining the action of the clutch worm I noticed that even in the optimum position the lever only rotates the worm towards the clutch over a distance of about 1/8". Are all laydown gearboxes arranged in this way ? Examination of an earlier upright gearbox clutch worm shows significantly more travel along the worm - and hence more lift of the plates - for the same amount of clutch worm lever movement through the arc. The clutch worms are not, of course, interchangeable. The machine is equipped with Tomaselli - type levers (replicas, I am sure) and I wonder if these may have a smaller range of movement than the original pattern although they do not appear particularly limited.

By trial and error in adjusting the cable adjusters at both the handlebar and gearbox I have reduced most of the drag but it is never far away ! 

Any advice would be much appreciated as I am new to Nortons.

Submitted by richard_cornish on Tue, 01/10/2019

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Hi Keith,

   Take off the oval inspection cover, take the cable out of the arm and undo the clamping nut. Use a straight blade screwdriver and screw in the worm to take up any slack, then turn back a fraction, push the arm down as far as possible while holding the worm in position and re-tighten the nut. Refit the cable and adjust to give a little slack and this is about all you can do unless you change handlebar levers.

   There have been many posts on clutch drag and this can be due to several reasons, but I've found plate distortion is a very likely cause when they get hot.

Submitted by ian_soady on Wed, 02/10/2019

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... needs to have 1.1/16" distance between pivot and nipple centre to get maximum lift. Although 1/8" travel (I'm assuming you mean pushrod travel) should be enough.

Submitted by keith_mountain on Fri, 04/10/2019

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Thanks to Richard and Ian for your very helpful responses. I was surprised that a generous arc of movement on the worm lever produced such a small axial movement along the worm gear itself, especially in comparison to that produced on the gear from an upright box when moved over a similar distance. Adjustment of the cable at both gearbox and handlebar has removed the worst of the drag in that the engine no longer stalls when the machine is brought to a halt in bottom gear with the clutch lever pulled in to its fullest extent. I`m beginning to think that the remedy may be to replace the clutch and brake levers with original specification types as these appear to provide a longer reach from the bar to offer a greater lift on the plates when fully extended. Could anyone recommend from experience particular levers from the usual suppliers ?

Submitted by ian_soady on Sat, 05/10/2019

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.. the bronze thrust washer on the gearbox mainshaft? In my very impecunious early Norton single days that was the problem I had with my first 16H / Model 18. It means that the first part of the pushrod movement is lost in pushing the mainshaft sideways.

I just bought a lever from ebay - the 1.1/16" pivot distance are quite common, especially for plain blade types. You mention adjusting at the handlebar - I believe that most levers with adjusters are actually 7/8" pivot distance.

I would imagine that virtually all levers available these days actually have a common initial source.

Submitted by colin_eggleton on Sun, 06/10/2019

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Hi,i have a model 18 and a dommi 88 with laydown boxes and both are on the limits regarding cable slack and clutch slip. I agree with ian regarding mainshaft end float. I re shimmed mine when I had them apart to about 0.003" if I remember correctly. still not great. I think new plates are probably the way forward. check the steel plates for deflection on a plate of glass and a feeler gauge. 

 


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