ATD Springs

[Big Sid]

My 65 years with British motorcycles began with a used 500 AJS single rigid rear end second hand bike in lovely condition .
This followed by a new Matchless 500 twin in 49 , it's first year in America . Next came the 51 Red Touring Rapide in 51, assembling it right out of the crate myself . Each taught me a great deal overlaid on the last machine , and this hunger to know more never left me .
Living in Norfolk , a huge Naval Base town , where a fresh crop of sailors was constantly arriving from all points , many on motorcycles of various brands , mostly British , had me meeting new pals and seeing all brands up close and often laying a wrench on them to correct a fault , set valves , adj. carbs . My classroom on Avons and Dunlops , my garage the shop .
My actual motorcycle business opened in early 74 and shut down as I retired in late 92 . During that time we worked on any and every thing from mopeds to Black Lightnings , Shadows and Rapides , Harley choppers to a Morgan front motored , a big Matchless vee twin , Ariel Sq. fours, and big Enfield twins . All manner of BSAs , AJ and Matchless , Velo , whatever came in the door .
I soon had to turn away choppers because they were prone to flopping over and taking out other bikes . Hated them anyway .
So that's the background from which I draw upon for my comments as best my memories allow . Sid .

 

[Martyn Goodwin]

It has been a while since I visited this topic and despite much work on ignition timing, magneto setup and ATD tweaking I remain bugged by the phenomenon of having a motor that once hot will not return to a steady idle speed .

To recap I run an original magneto and an original ATD .

With the ATD off the bike - and cold - it returns smartly from the full advance position to the full retard position. And I assume it also does so when fitted to the bike, for , from cold, over the first 20 to 30 minutes of operation the motor will return to a steady idle. However once well and truly warmed up the idle speed increases significantly. Stationary, if I engage first gear and slip the clutch I can 'pull' the revs down to a sensible idle but as soon as I pull the clutch in the revs rise!

I gave this some thought and figured it must be temperature related - that the engine heat was somehow reducing the ATD spring force but allowing it to return when the springs cooled down.

Today I discovered the attached article which confirms that this is expected spring behaviour!

I have spoken with a local spring manufacturer about the issue and that have said they can custom make some ATD springs in a grade of material that will NOT exhibit this problem provided the springs get no hotter than FIVE HUNDRED degrees Celsius. I figure that's well within the temperature rise in the timing chest!

I am waiting on a quotation from them though they did warn me that the wire to be used was around US$3,000 per Kg. I have asked for a quote for 2 sets and also for 20 sets as I suspect anyone who actually rides their magneto equipped Vincent must experience this issue.

So if that's you, would you be interested in a set of heat resistant ATD springs?

Martyn

 

[passenger0_0]

Nice theory however I'm not sure Martyn that you'll see temperatures above 200 degrees C within the timing cover.

 

[timetraveller]

I am also suspicious. Clearly there are spring for which this is not a problem, e.g. valve springs. I know that the outside of a crank case gets hot enough for water/spit to bounce off it (leidenfrost effect for those who care) but can the springs, spining round in hot air and covered in oil and vapour really get hot enough to loose there tension? This would be a nice little experiment for someone with an accurate temperature guage and some way of tensioning a spring and measuring its length whilst hot.

 

[Martyn Goodwin]

Nice theory however I'm not sure Martyn that you'll see temperatures above 200 degrees C within the timing cover.

My local spring maker advised that their 'regular' springs of the ATD spring size would exhibit this temperature effect from around 80 degrees C and upwards, especially if made from what they described as 'black spring steel' whatever that is.

My comment was I would not expect more than 200 C so a material designed to work up to 500 C should be just fine.

I wonder what the material specification is that's used by the VOC Spares co when they order in these springs? PR22A/D. Is it possible that they DO NOT specify the material at all, just the dimensions?

 

[bmetcalf]

I wonder if the springs on Roy Price ATDs are different than Lucas units? I have a 10 year old Price unit and it is doing the same as Martyn's. A 2020 thread has some info on a Tony Cooper making the Roy Price style, does anyone have news on that?

 

[Peter Holmes]

I would imagine, but I don't know definitively, that Lucas stopped making and supplying ATD springs a very long time ago, in all probability what we have had since is springs that are dimensionally correct, but maybe the specification is not quite correct.
I doubt that Roy Price or Tony Cooper manufactured or had manufactured springs to Lucas or their own specification and probably sourced them from suppliers of pattern parts, for example, Wassel or Feked etc. It might not even be heat related, it could be a replication in reverse of what Gregg recommends if your camplate detent spring is too strong, squash it in a vice once and reduce the strength of the spring for good, I guess the wrong specification ATD spring could easily lose its effectiveness once stretched, and perhaps the original specification Lucas spring did not suffer from this.
Was it not the case that the original springs lasted so well in tension the spring ears in time simply wore away and then the springs detached themselves and ended up at the bottom of the timing chest, if you were fortunate that is.

 

[bmetcalf]

Martyn,

So if that's you, would you be interested in a set of heat resistant ATD springs?

To answer your question, yes.

 

[vibrac]

I wonder if the springs on Roy Price ATDs are different than Lucas units? I have a 10 year old Price unit and it is doing the same as Martyn's. A 2020 thread has some info on a Tony Cooper making the Roy Price style, does anyone have news on that?

I am not sure but Tony may have given up manufacture I would not be surprised I think given it is an item with many parts to make and sell at a price the market will take (given the growing alternatives) and stay profitable

 

[oexing]

My guess, the springs are the wrong tree to bark up to. Springs are heat treated to higher temperatures than you´d ever see in an engine. A strobe would tell with hot engine - or alternatively you´d check spring force with some scales when fresh out of oven - no difference I´d think.
An engine will have higher idle speed when hot, just normal, but if too high it may be related to valve clearances - not likely with Vincent engines. What grade of engine oil is used - 50 monograde ?? It takes quite some while to heat up the oil , try minimal oil in tank for shorten time till high idle ?

Vic