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ATOM Unit - help please ?
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Sponge
Lancashire (A chip shop somewhere near Preston)
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July 8, 2019 - 9:16 pm
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I have a D7 that is fitted with one of these postage stamp sized atom ignition units.  It is situated where the condenser would normally be. There is no points or condenser in the magneto 

The little bike starts well and runs fine but how/why does it work ? can anybody help and how do you set the timing ??

I think it originally came from C&D autos in Midlands. 

 

Sponge

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swalsh58
St. Mary's Bay, Kent
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July 8, 2019 - 9:34 pm
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I am a firm believer in the principle that if it isn’t broke, don’t fix it. If it’s running well, leave it alone! Find out how to adjust the timing when/if you need to. I think these units are SFL and have no consumer repairable parts inside. 

If your desperate for information try contacting C&D, I have always found them very helpful, they may have a copy of the instructions you could have. A word of warning though. I have found as I get older that each new piece of information I force into my brain, automatically pushes a previously stored nugget of information out. Now, where did I put 10mm socket....

Current bikes......1958 D5, a 77 Suzuki GT250 and a 77 Honda CB125S. I have a B175 in the workshop and a 76 Honda C90 waiting its turn. A 1980 Honda CB400N waiting for MOT.  Everyday ride is a 2011 Harley Davidson Sportster. 

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sunny
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July 9, 2019 - 7:29 am
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 i  think  you  will  find  C&D   are  the chapes  that  first  sold  the  ATOM  And  a  ht coil with  a  SCREW  fiting  for  the HT lead      both  very  good   ,,  how / Why  has been  coverd   befor   wot  is   also  inportent    is  that  the things  that need  to  get  fixed  like   the  end  of  the  crankshaft at  the oilite   bush  need  to  be  in  very   good  contion    as   with all  engines    uther  units  have  also  been  used    coz     the  ATOM  &  the  coil  are  hard  to get  not   made  eny moor   do  a  SERCH    from  the  top  of  the  page

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jolon1
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July 9, 2019 - 1:05 pm
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Rooster did a unit, very similar to the Atom. Unfortunately, paxo, who owned the company passed away a couple of years ago, but I think you can still get info on the club website, as He was a member. I didn't know you could get rid of the points though. There is another similar unit on Amazon, for lawn mowers. Read the reviews as I think someone mentioned using one on a two stroke motorcycle.  

D7 & D1 Racer

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cocorico
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July 9, 2019 - 4:33 pm
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If I recall correctly, the semiconductors in the unit sense the peak magnetic flux generated by the rotor in the primary coil, then work their magic to send it to the secondary. Don't ask me how, though.

1956 D3 running, lights to sort. 7 other bikes in the Barn, including a Morini 250 now running nicely, almost road worthy.

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Sponge
Lancashire (A chip shop somewhere near Preston)
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July 9, 2019 - 4:45 pm
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Many thanks for the responses. It certainly works well but I am suspicious about ignition timing - how can it possibly know when to trigger the spark ?

Reason I ask is because the bike seized up the other day.  It has never done that before, after 30 years of careful use, everything was fine ( starting, fuel, carb etc) but I suspect it was due to incorrect ignition timing !!!

I am also concerned about where it is located inside the magneto timing cover. It gets quite hot in there and I was wondering if the heat was having an effect upon the ignition timing.

Also if you don't give it a good kickstart it can run very well backwards - very surprising when it happens, especially if you stall at the lights then give it a kick and try to make a quick getaway to save face - straight into the front bumper of a Range Rover !!! Despite being very rich those Range Rover owners do not seem to have much sense of humour do they ? 

Everybody should spend a week or so depending upon a Bantam (or other small BSA) as everyday transport - it would change their lives. 

I wish I knew more about the Atom unit though ......

 Sponge

 

   

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mike p5xbx
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July 9, 2019 - 5:02 pm
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Sponge said
The little bike starts well and runs fine but how/why does it work ? can anybody help and how do you set the timing ??
 

the timing is set by the Atom you cant alter it
( they did actually make 4 different ones for chainsaws lawnmowers etc with different timing needs)
it works by the changing voltage from the flywheel magnet passing over the HT coil and switching on and off just like the points do
however they were all made for engines with only one magnet
(so only sparked once every 1 or 2 revolutions)
not the multiple ones that the bantam has with lighting coils
which is why they can fail unexpectedly, more so for the Nova type that are sold now
they only really work on 4stroke lawnmower type engines

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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Piquet
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July 10, 2019 - 12:49 am
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Difficult to describe. They can only work on magneto type ignitions. The magnets are not randomly situated around the flywheel, they are precisely located in relation to the key-way.

Think back to the standard ignition, the coils/magnets are arranged so that the maximum flux is generated at the timing point, ie. when the points open. If you were to remove the flywheel woodruff key and put the fly wheel back in any other position and lock it on the taper, there is a good chance that the ignition will no longer work. The points and timing can still be correctly set but if the current being generated does not correspond to the timing point then the result is a poor spark at best or more likely no spark at all.

Back to the Atom and similar units, if the flywheel and coils are correctly located then the maximum flux is generated at the timing point, the circuitry in the unit senses this and uses it as the position to create the spark. It only works because the D1-D7 Bantam engine is not very fussy about ignition timing and as long as the spark occurs somewhere close to the specified timing point the the engine will run. It also explains why it is so easy to start and run backwards, the timing (magnetic flux) is virtually the same in either direction.

I'm not a complete idiot ............................................ some parts are missing.

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mike p5xbx
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July 10, 2019 - 5:16 pm
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You could in fact move the flywheel to alter the timing if you have an Atom fitted
(maybe that has already happened with yours re the seizure)
as it does not suffer the same points position problem
but without it being held in position by the woodruff key there is always the risk of it moving and timing being well out or not running at all
this is the circuit diagram for the Atom if anyone is interested
about £4 worth of components
Atom4.jpg

sp_PlupAttachments Attachments

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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BSAdave
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July 11, 2019 - 10:05 am
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Ive been running my D3 with the brown atom unit without any problems for a long while, no points fitted, what the Atom instructions do say is you need to mount it away from a heat source. I would move it away from inside the points cover. Can't help with how it works, but from my experience it works well. I have tried thge pink Atom unit and this one does not work, if the unit is faulty I don't know.

The Brown ones are hard to find now.

I could agree with you, but then we would both be wrong

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thornebt
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July 11, 2019 - 1:10 pm
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BSAdave said
Ive been running my D3 with the brown atom unit without any problems for a long while, no points fitted, what the Atom instructions do say is you need to mount it away from a heat source. I would move it away from inside the points cover. Can't help with how it works, but from my experience it works well. I have tried thge pink Atom unit and this one does not work, if the unit is faulty I don't know.

The Brown ones are hard to find now.  

I've also got a brown Atom unit on my D1 - inside the points cover.  It works fine and I prefer not fiddling about with points.  Cheers.  Bruce.

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