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Dominator clutch operating helical scroll

Submitted by george_arber on Thu, 12/12/2019
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Heavy Twins

Your Xmas challenge ! 

Can anybody advise me as to the helical pitch of the clutch operating scroll which actuates the clutch pushrod on my 1956 Dominator 99 ? The gearbox is a laydown model. The rotational movement via the bell crank lever is approx., 45 deg., and I am interested to know the theoretical transmitted axial movement.

George 

 

Submitted by jonathan_newton on Thu, 12/12/2019

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George; not sure why you are not measuring the true physical movement.  With adjusted gap, pivot losses, pull angle and variable wear point on the scroll you would rarely achieve the  theoretical movement. 

 

 But I will measure it for you tonight, there is one on my bench...

 

Cheers

 

Jon

Thanks Jon for your reply. 

Yes, I have measured the axial movement at the clutch with a DTI. It measures a knat's whistle  of  around 0.040". I am in the process of having another go at setting the clutch movement and see if I can obtain an improvement.

If you check out the earlier various messages and replies on the heavy twins section on the subject you will see my reasons for my earlier queries too.

Regards,

George

 

Submitted by george_arber on Thu, 12/12/2019

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As I cannot get the bell crank lever to a full 45 deg., with the cable adjuster fully screwed in, I am beginning to suspect that the clutch cable is too short preventing me to improve the anti clockwise start point. 

 Am I  on the right trail here ?

George

Submitted by michael_sullivan on Thu, 12/12/2019

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With the clutch lever released, how much freeplay do you have in regard to the outer cable?

Mike

 

Splendid job George.  Didn’t realise you had ongoing dialogue. It’s maximising that travel by making sure you get the most effective part of the stroke translating the direction of travel.  That means your given amount of travel dictated by your handlebar lever (7/8” fulcrum) needs be halved across the bell crank movement.  (Half the given movement should bring the bell crank to its most effective angle.

At that point you then need to adjust your combined lengths of scroll, rod and mushroom to suit the released handlebar lever position.

teaching, eggs and sucking come to mind now.

 

It’s small stuff but nothing worse than a clutch that won’t clear.  cheers

Jon 

Submitted by paul_standeven on Fri, 13/12/2019

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My clutch is in good condition, but with a 7/8" pivot clutch lever, I find that the mechanism has to be very well adjusted to avoid drag.  And get neutral before you stop, or the slight drag causes warming which causes more drag......

What I do is release the clutch lifter arm from the centre shaft, push it down as far as possible, hold it down, tighten the quick-thread centre with a flat bladed screw-driver, and with my third hand tighten the lock-nut.  It must be a bit like key-hole surgery

Paul

 Thanks you all for your replies. Whilst having a cup of coffee this morning it dawned on me that fitting a slightly longer clutch cable would get the bell crank lever to the 45 deg., start position but would in fact make no difference to the movement of the push rod ! The arc of rotation of the scroll is dictated by the movement of the clutch lever which has a 7/8” pivot.

Just another ‘ senior moment ‘ . I seem to getting a lot of these lately.

I have approx., 1/16” free movement at the clutch lever and I fitted a Bob Newby clutch and primary belt drive which reduced the drag somewhat so that neutral is a little easier to find but I really would like to get some more movement of the clutch push rod .

George 

 

Submitted by ian_soady on Fri, 13/12/2019

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a 1.1/16" clutch lever? I can't remember if it was you posting re clutch worm some time ago.

I use a 1.1/16 clutch and 7/8 brake on my ES2 and they work well.

Submitted by richard_payne on Fri, 13/12/2019

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Is the worm the same as on the Doll's Head boxes ? Pre-war, Norton used levers with 1 1/8" pivot centres which give substantial lift.

Did the post-war factory forget the reason why, or did AMC force buying economies ?

Ian's solution sounds like a good one. 1 1/8" does give a lot of lever travel for the front brake making it difficult to adjust for an easy reach.

Submitted by paul_standeven on Fri, 13/12/2019

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My '55 Model 88 came to me with 1 1/8" pivot levers for clutch and brake.  I think that this was standard until the AMC box came along. 

I fitted the 7/8" levers for a lighter clutch (not that it was heavy before) and better brake pull (my 8" iron/alloy hub is wooden despite bonded machined linings)l,  and accept the consequence that I have to be careful with clutch lift and drag.

Paul

 


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