Author Topic: K2F ATD Unit  (Read 239 times)

Offline scotty

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K2F ATD Unit
« on: 18.05. 2020 15:05 »
Looking at my ATD unit on the bench and the springs do not close the mechanism (to retarded position) all the way home when I release them.
All moving parts move freely
Not really sure how to verify if unit has serious wear
Left it soaking in oil overnight but still the same

Should the springs completely close the mechanism on the bench when operated by hand?
Can I replace the springs without taking the unit apart ?

Enquiring minds and all

Cheers

S
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Scotty

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Online morris

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Re: K2F ATD Unit
« Reply #1 on: 18.05. 2020 19:51 »
It should close up as good as
I think the springs can be changed without dismantling
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Offline scotty

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Re: K2F ATD Unit
« Reply #2 on: 19.05. 2020 00:02 »
Morris

Thanks for taking the time to do that !

I think my springs may be pooched.

Cheers

S
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Offline Scott and Jay

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Re: K2F ATD Unit
« Reply #3 on: 19.05. 2020 05:14 »
Hi scotty,

When I rebuilt my A10 motor, about 8 years ago now - I was attracted by a post (I think it was on the Britbike forum), that recommended these "strong" ATD springs. It was from an unusually-named supplier - "Eurotrash Jambalaya". They arrived in the post promptly. They seem to specialize in spring sets and other (stainless) bits, for classic bikes. This is the link to the equivalent springs, today:-  https://www.eurojamb.com/collections/bsa/products/bsa-441-500-650-750-auto-advance-springs-b44-a65-new
My removed ATD then snapped back to fully-retarded, and has worked fine in place - delivering a smooth power curve, ever since...
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Offline scotty

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Re: K2F ATD Unit
« Reply #4 on: 19.05. 2020 06:26 »
Thank you good sir

I’m going to look into that

Cheers

S
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Scotty

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beezermacc

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Re: K2F ATD Unit
« Reply #5 on: 19.05. 2020 07:58 »
Critically, the ATD needs to return fully when at rest so that upon startup you can be sure the bike isn't going to kick back. Once the bike is started it is important that the bob weights open fully to achieve full advance. What happens between startup and full advance isn't as important as some might suggest. If the springs are strong enough to return the ATD to its closed position they are probably about the correct strength. I have found that very light springs won't overcome the friction in the ATD itself and, having fiddled with ATD's for years I've got a pretty good grasp of which springs feel about right. Remember we are talking about low powered bikes which are quite forgiving in terms of their setup. The ATD needs to operate smoothly so that there aren't any sudden 'notches' in its operation and needs to achieve full expansion somewhere approaching 2000 r.p.m. (I guess) or the pipes will turn blue due to retarded ignition. The springs I use are cheap and cheerful, they feel about the same strength as originals, so I just make sure the ATD returns fully by 'adjusting' the springs so there is a little bit of tension applied when at rest.
I get occasional phone calls from customers saying that the springs aren't strong enough because the ATD works in the hand but not on the bike when at rest. This is normal due to the various counter-forces in the magneto. If you turn the engine over very slowly with the kickstart you should see the ATD close completely which reassures you that the bike won't kick you back next time you start it.
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Offline Swarfcut

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Re: K2F ATD Unit
« Reply #6 on: 19.05. 2020 09:24 »
 Scotty.   I've rarely seen an ATD which didn't rattle a bit when shaken, the amount of rock on the main spindle and the wear on the bob weight pivots were par for the course on any used unit. The problem you have is simply down to internal friction from wear in general and as the pivot point axes are no longer truly in their designed positions so the existing old weak springs cannot exert their full effect. Wear on the bob pivots and lever arm pivots alters the geometry of the set up.

 As BM suggests, a change of springs may effect a reasonable cure. Springs can be swapped without dismantling the unit.  Flip the spring end off the vertical post, then unhook from the lever.

  Apart from retarding the ignition for starting, the unit spends most of its time fully advanced and despite appearing on its last legs should still function just fine for leisure riding. 

 Swarfy.
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Offline scotty

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Re: K2F ATD Unit
« Reply #7 on: 19.05. 2020 13:42 »
Thanks all !!

Great info !!

S
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Scotty

Current liabilities:
'56 A10 Red Flash
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'98 HD FLHTPI
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