Clutch issue

[Simon Dinsdale]

I note a sticky ATD being mentioned as a cause of fast engine idle. I don't believe that to be correct.

If the throttles are closed to their normal idle position and the ignition remains advanced as the engine slows down, then the engine will idle slower, not faster, and will often stall. This is easily verified by adjusting the timing on a running engine by turning the distributor - as the ignition timing is retarded the engine idle will speed up.

In summary, sticky ATD will result in an engine that idles slower, idles rough, and is difficult to start.

Sorry but you are definitely wrong. If the atd stays advanced at idle the idle speed is high. Just try advancing the ignition lever on a bike with manual ignition control on the handlebars at idle. It increases the idle speed. Having two bikes with manual advance, one a Vincent, both bikes do this. Retarding the ignition lever returns the idle to its correct speed.

An atd is fully retarded when the springs pull it against the stops. When the rpm increases the weights advance the ignition against the springs. If the atd is sticking the or the springs are weak then the atd remains advanced or reacts too slowly as the rpm decreases to idle.

 

[kurtflys]

OK another dumb question. Were all the nuts and bolts on a Vincent Whitworth or were there SAE stuff also?

 

[A_HRD]

OK another dumb question. Were all the nuts and bolts on a Vincent Whitworth or were there SAE stuff also?

Nearly all the nuts and bolts on a post-war Vincent were British Standard Fine (BSF). There are a few exceptions where Cycle Engineering institute (CEI) - more latterly known as British Standard Cycle (BSCy) - were used; such as the nuts that hold the brake-arms to the brake plates - and those that hold the rear torque-arms on; and all over the place on Brampton forks. Then there's the usual sprinkling of British Association (BA) threads such as in mags, dynamos, carbs and other places too. There is actually very little whitworth around - with the exception of threads in Al Alloy - usually where covers screw on. There's a whole appendix devoted to this subject in Know Thy Beast.

If you're asking whether UNF or UNC were originally used on Vincents, the answer is no, none. But many US-owned Vincents in particular seem to have quite a few of them fitted - whether they fit properly or not!

Peter B
Bristol, UK.

 

[b'knighted]

What this should mean to you is that the spanners you use will be labelled BSW or BSF rather than AF. As an example a ¼ BSW spanner is also used on 5/16 BSF and is actually 0.525 inches between the flats. Using a 14mm (26 thou over) or a 9/16" AF (38 thou over) may work in an emergency but will eventually round off the nut.

http://www.sat.dundee.ac.uk/~psc/spanner_jaw.html may help

 

[vibrac]

Once again as the old comedian said
"You lucky people"
Not only did the threads stay the same and consistent but Eddie (Know thy beast) Stevens tracked down 98% of them for you.simply turn to the back of the new testament and read
Just try one of the products from the Birmingham/London parallel twin Mafia especially during their thread change over periods.....

 

[kurtflys]

I managed to get the ATD cover off with a little liquid wrench and when I rotate the unit to the right and release it it only goes about 3/4 of the way back to the stops, and not quickly. If it is suppose snap back it doesn't. I did not see a picture of the ATD in the parts book. You also mentioned "small tools". Are there special tools or just small screw drivers and the like?

Do you think Coventry might have the springs?
Thanks

 

[kurtflys]

My ATD does not spring back against the stops, but stops about half way or perhaps 3/4 of the way. And it does seem like the springs are weak. How many weeks will it take for me to change the springs=(

Sorry but you are definitely wrong. If the atd stays advanced at idle the idle speed is high. Just try advancing the ignition lever on a bike with manual ignition control on the handlebars at idle. It increases the idle speed. Having two bikes with manual advance, one a Vincent, both bikes do this. Retarding the ignition lever returns the idle to its correct speed.

An atd is fully retarded when the springs pull it against the stops. When the rpm increases the weights advance the ignition against the springs. If the atd is sticking the or the springs are weak then the atd remains advanced or reacts too slowly as the rpm decreases to idle.

 

[b'knighted]

While it is fitted the pinion is held in position by the timing gears and the magnetism of the mag gives the armature a favourite stopping place so the tiny ATD springs may not return it to the stops while the engine is static. Watch what it does as you turn the engine over as you may see it move to full retard then stop partially advanced.
I don't think that I'm explaining this very well but perhaps someone else will recognise what I'm trying to say and clarify it.

 

[Holger]

What you are describing is a positive feedback loop... Advancing the ignition timing causes the engine to speed up which causes the ignition to advance which causes the engine to speed up which causes the ignition to advance... etc etc

One other point is that if the combustion chamber mixture is ignited such the combustion is complete before the piston reaches TDC, then isn't the power from the combustion trying to push the piston back the way and thus slow it down?

 

[Martyn Goodwin]

My ATD does not spring back against the stops, but stops about half way or perhaps 3/4 of the way. And it does seem like the springs are weak. How many weeks will it take for me to change the springs=(

I had the same problem woth my Comet - I am using a Magneto. There are a few things to try. First up a liberal spray of WD-40 into/over the ADT mech just in case there is any old gummy oil on its pivots then give it a good workout by hand operating it full travel a few times. Next you need to go to the other end - the points within the magneto and make sure they also operate well in respect to the points cam. In a magneto you will have a ring cam and again WD-40 should be used to clean the rubbing surface and once clean then a small touch of hi temp grease onto the cam surface - I use a "cotton bud" to apply it with my magneto.

If you still have issues then you may want to try replacing the ATD springs. There are 3 grades of spring available from the VOC Spares company - Standard, stronger and bloody strong, however before you start playing with the springs it may be useful for you to look at this site

http://brightsparkmagnetos.com/faqs... is the spring rate and preload in an ATD.htm

The VOC Spares Company springs part numbers are:

407256 - Velocette heaviest,
416060 - 500cc AJS/Matchless middle, (BTW These are what I have fitted to my ATD)
498154 - lightest all others including Vincent, Norton, BSA etc, etc.

Here is a link to the VOC Spares Company

https://vocspares.mamutweb.com/Account/Logon?ReturnUrl=/Shop/List

And finally, from the archives, Big Sid's instruction on changing ATD springs

" One can often shorten a spring that fits loosely by cutting off the end loop and bending over the next one or the second one if careful . With the cover off and the center nut still tight so it's taper is well set you proceed as follows . Carefully back off on the center nut just enough to slip out the horseshoe and tin disc so revealing the springs . Go easy not to back off the inner removal mechanism .
Change the springs , now accessible , be sure they tug on the peg , not hang loose , trim off the end loop and reform if needed .
Tuck in a piece of cloth below in the opening to prevent dropping in the spring ! Remove the cloth . Replace the tin disc and the horseshoe washer . If this is bent up , often is , flatten it first . Re tighten the center bolt holding all in position carefully .
Replace the cover . All done . Good luck . Sid . "

Hope this is of some help

Martyn