The BSA A7-A10 Forum
Bikes, Pictures, Stories & more => Wanted & For Sale => Topic started by: chaterlea25 on 19.10. 2020 21:02
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Hi All,
Has anyone got a spare ATD unit in good condition going spare ? currency or maybe swops ?
I have ordered an electric start kit from Steve McFarlane for my SR which has manual A/R
Steve insists on fitting an automatic ATD to prevent damage to the sprag clutch
I have missed out on a couple of units on ebay and others on there look rough
Covid permitting my knee replacement is booked for a months time, *eek* *work*
John
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Steve insists on fitting an automatic ATD to prevent damage to the sprag clutch
How does he work that one out? Not often, but have had engines kick back on me when the A/R unit has stuck in A. Doesn't happen with manual.
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Hi RD,
TBH I don't know
I did suggest a splitter on the A/R cable the second leg of the cable would operate a micro switch to prevent the starter operating without retarding the mag
Steve rejected this idea *sad2*
John
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On a tangent, John, do you know the reduction ratio of the starter 'twixt motor and crank? I ask because I have in mind constructing a starter for the project. I know cars / trucks generally run around 1:15, but what about bikes?
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Hi RD
It will be a month or so before the kit gets here so I don't know the reduction
It is probably worth asking Steve explaining your project
Stephen.McFarlane73ntlworld.com
John
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Good luck with the operation Chaterlea, hope it goes well.
Whatever his reasoning, it will be sound..... He's nobody's fool when it comes to engineering as you no doubt know, with a long list of successful projects and solutions to problems behind him.
Did he not offer an explanation when he poo pooed your idea of a micro switch?
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On the adv / ret starter theme, I thought most had a shock absorber included in the train. My Firestorm kicks back against the starter sometimes, and that has electronic ignition with presumably some sort of automatic advance mechanism.
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Commandos have a one way sprag as do Enfields. My goldie with Pearson starter has one way ratchet.
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Hi All,
I have an original BTH magneto fitted and from my experience it gives easy starting with the lever pulled back enough to prevent kickback, But I do not want to risk damaging the electric starter drive components for obvious reasons
This is what Steve wrote in his reply to me
"problem is that the more you retard the timing manually the weaker the spark gets due to the magnets not lining up with the coils in the armature and there is often not a strong enough spark to start the engine with the electric starter
You have to fit an automatic advance retard, sorry"
Below is the text from one of the information pages sent with the initial reply
""The amount of technical ability needed to fit the electric starter:
You will have to have the ability to strip and re-build an A10 engine, or know someone who has.
It is now where as much work or as difficult as striping and re-building an engine but that is the sort of ability you will need.
You will also have a motorcycle bench lift or have access to one
Good set of workshop tools
There is a small milling job to be done so you will have to have access to one or know someone who could do a small milling job.
N.B.
I have now fitted a few electric starters and I have found that when using the electric starter they are far more sensitive to kickbacks. A bike that doesn’t seem to kick back with a kick-start can kick back when using the electric starter.
I have found up to 14 degrees difference between the 2 firing intervals with the K2F magneto, with a typical difference being about 3 to 5 degrees
So if you time up 1 cylinder to 33 degrees BTDC fully advanced the other cylinder may be either 28 or 38 degrees BTDC it is important to get them the same for good running of your bike and also to prevent a backfire, which can damage or destroy the sprag clutch.
There can be quite a few causes of this problem, which I will let you know the main ones in another e-mail but in the meantime,
To properly check your timing you will need.
1 degree disc
2 spark plug DEAD STOP, not a TDC plug tool
3 one of these special timing lights specially made for magnetos
4 pointer
Picture of the equipment enclosed""
John
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"problem is that the more you retard the timing manually the weaker the spark gets due to the magnets not lining up with the coils in the armature and there is often not a strong enough spark to start the engine with the electric starter
You have to fit an automatic advance retard, sorry"
So the automatic A/R gives a different type of retard to manual (more advanced for a better spark)? The guy would make a good politician with that sort of nonsense.
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Hi RD,
The ATD does not alter the relationship /timing between the magnets / armature and the points opening position.
The manual advance does affect this so regarding weakens the spark
John
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'Fraid he is right RD.
From the point of view of a piston or crankshaft, 'retard is retard' pure and simple. But not from the point of view of a magneto it isn't, far from it.
Retarding the camring by moving it alters the relative strength of the spark by delaying points opening with reference to the point of maximum flux change of the magneto.
Spark strength drops off very fast with retardation of points opening. You can see this on the bench with any manual camring magneto just by flicking it round in the advanced and then the retarded settings - you'll get a better spark with less effort when it's advanced.
Using an ATD to alter the relative position of crank and magneto drive ensures the spark always arrives 'fully advanced' from the magneto's point of view. The spark is therefore full strength, regardless of where the ATD is in its range of movement. ATDs may be crude and hateful things in many ways - but they have this one important and undeniable advantage. If you ever try to start a large V twin using a manual mag on full retard . . . you'll see how weak the delayed spark on the second cylinder can get! Which is why Vincent were early adopters of ATDs, and why Indian went to battery and coil ignition even before they had decent dynamos to support it.
If a lot of retard plus best possible spark is what's needed to avoid breaking the sprag clutch on the 'leccy leg (I have no experience with them myself), then an ATD is unquestionably the better route.
You beat me to it John.
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john , i had full rhs knee replacement and after 6 - 8 months i was back kickstarting. but you do avoid struggling i.e. non starts
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So the automatic A/R gives a different type of retard to manual (more advanced for a better spark)? The guy would make a good politician with that sort of nonsense.
Yes, it does.
Actually, he'd make a very poor politician, he knows what he's doing and what he's talking about! *smile*
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thanks groily your post has just confirmed what I found out messing about with two manual mags, and not being up on these things has now put my brain cell to rest, I can see clearly now the rain has gone, song in there somewhere *whistle*
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Of course, you're right chaps. My apologies. Brain fade I'm afraid. The only case I could think of where spark is not reduced by retarding was the old impulse magnetos on older stationary engines.