Thorspark Electronic Ignition

[bsa-bill]

You don`t have to kick start an aeroplane engine,cheers

Excuse me, according to Les Dawson his mother in law kick started Jumbo jets 

[Stu55Flash]

The sparke is started by the points just starting to open so how does changing the points gap affect the timing? From the various bike I've had the next development iteration from the 1950's was to keyway the shaft mechanically fixing the magneto to the timing on the crank. The points back plate could then be moved to alter the timing - but again the sparke was initiated by the points just starting to open. The points gap was set independent to this not affecting timing.

Not sure of the logic of using the points gap for timing?

Stu

[bsa-bill]

altering the points gap moves the fixed point, the moving point therefore rests at a different place when closed which means the fibre heel is nearer or further from the cam-ring so it contacts the cam ring ramp sooner or later opening the points quicker or later

[Alan @Ncl]

I think Bill is quite right and he explains it nicely (but then, we North Easterners always support each other when facing the world beyond).  I did not realise that there was a generation of keyed mag shafts though.  Would the autoadvance pinion on these need to to have a unique matching position relative to its driving pinion with some kind of mark (similar to the camshaft drive)?

And can I just check with Marcus, if you have an auto-advance, how easy it is to actually see where the timing is with the strobe?  With a lightly damped mass spring device like this in the drive train to the mag, I can imagine the timing dances all over the place until the engine revs are high enough to drive it it hard up against the fully advanced stop?  Presumably you have to keep the revs up above some threshold if you want to be able to see what is going on?  This will also apply when setting up a Thorspark system as they recommend using a strobe to set up too.

Also, once you have set it dynamically like this, how well does the timing correspond to what you get using the old static 'fag paper' or the 'timing light across the points' method?

[Triton Thrasher]

 I did not realise that there was a generation of keyed mag shafts though.

I don't think any thing like that appeared on old Brit bikes.

And can I just check with Marcus, if you have an auto-advance, how easy it is to actually see where the timing is with the strobe?  With a lightly damped mass spring device like this in the drive train to the mag, I can imagine the timing dances all over the place until the engine revs are high enough to drive it it hard up against the fully advanced stop?  Presumably you have to keep the revs up above some threshold if you want to be able to see what is going on?  This will also apply when setting up a Thorspark system as they recommend using a strobe to set up too.

Also, once you have set it dynamically like this, how well does the timing correspond to what you get using the old static 'fag paper' or the 'timing light across the points' method?

The strobe image is pretty steady. At idle, you sometimes get an occasional flash out of position. Rev it up and it advances fairly smoothly to the fully advanced position. You have to rev it high enough that it stops advancing.  If the points pivot is worn, you can get strange timing effects at speed, that might make you glad you checked with a strobe.

[Alan @Ncl]

Thanks TT on both points.  I note you say its steady at idle as well as at the fully advanced position.  This makes sense as its hard on the two respective stops.  Its particularly interesting though that it also stays steady in the intermediate range which suggests it is very stable and progressive after all (I seem to recall seeing somewhere that it tends to behave more like an on off switch than a proportional device, which is what it is supposed to be).  Good point about showing up things like worn pivots too.  I was wondering though if the timing you arrived at with the strobe came out the same as you thought you had with the old method and if not, which direction, and how far, was it different?

Alan  

[Triton Thrasher]

I found, with good points etc., and a new auto-advance I found no difference worth talking about, between strobe and fag paper timing, but if you never do strobe timing, you'll never really know what the timing is doing when running.

With a badly worn points pivot and a solid pinion, so it was fixed at full advance, the timing jumped from about 39 degrees to about 45, at something over 2000rpm.  Quite scary!

At low rpm (and while setting timing with fag paper), I think the slop in the pivot was taken up before the points opened. At higher rpm, the points were getting knocked open instantly, through an inertia effect. That's what I theorised anyway.

[Alan @Ncl]

Thanks TT.  Useful info here.
incidentally, walking back from the pub tonight, I realised I had stated in an earlier post on this thread that I had read that 1 thou of points gap equated to 2 degrees of timing difference.  On reflection I think what I read might have been one flat of the CB screw equated to 2 degrees.  Somebody will have the answer to this?  Apologies if I have misled the brotherhood.

Alan

[bsa-bill]

You were right first time 1 thou = 2 degrees, this courtesy of Trevor.
This is a powerful bit of info and allows fine setting of timing provided you are deft enough with a feeler gauge, most feeler gauges go down to 1.5 thou, I have discovered a set advertised as going down to 0.0006 ( 6/10ths of a thou ) hopefully this is not a misprint (others sellers stating the same). will report back if they are wrong

[Brian]

Jusy for interest here is how BSA recommended to find TDC and set the timing.

[groily]

And if anyone wanted a proper drawing of the modified cam ring locator peg I mentioned above, thanks to he who did it I now have same. Slightly at odds with what I remembered, it actually gives 8 degrees variability (crank), uses the same 1/4 bsf thread that is there but with a 5/16ths one-off locknut on a stepped shank - and is a simple turning exercise. It doesn't look like a carbuncle.
I'd be happy to send it to anyone as an e-mail attachment. But can't attach here as despite it's simplicity it's a pdf file and over the 600 wotsit limit and I'm too dumb to know how to shrink it.

[Stu55Flash]

I always believed the the auto advance is there to ease starting and reduce kick back fire, therefore when running it should be in the advanced position? Although I don't know where I've had this from.

All this talk of perfect ignition worries me a bit as the best bit about riding my bike is the odd mis-timed spark especially around the country lanes when between close in buildings I can open the throttle and rattle some misfitting window panes. The day it gets that perfect it runs like a japanese sewing machine I will give up!

Having said that I am also having hot starting problems. I dodged a mag rotor rewind on rebuild much to my regret. I am now thinking along the lines of stripping the mag HT wires from the rotor and connecting the low tension to the slip rings and connecting this to an external coils via the pick up leads. This way the ignition works independent of the battery, uses the mag to generate the pulse and time the engine, looks the same and has the advantage of an external ht coil.

Has anyone tried this approach?

[lawnmowerman]

Don't see why it would not work Stu with the addition of an ignition switch. It would still be dependant on the battery though to power the coil as you will only be sending an interrupted earth to it and I think you would still need a suitably sized capacitor in circuit. If it could work it will be a fairly cheap fix.
There was an older topic about jury rigging where the HT was fed through a second coil but I think only with limited success.

Jim

[Alan @Ncl]

I am falling behind a bit as there have been a few interesting recent posts here. Working back from the most recent, I am really intrigued by Stu's idea and the variation on it (as I understand it) from Jim.  Both certainly worth further exploration.

Next Groily: I would appreciate a copy of your pdf please if you can send to alan.fowler@ncl.ac.uk. Nice sanity check from Brian also noted.

Then to Bill and the issue of how much timing adjustment you can get on the points.  I have been playing around with this wondering where the numbers come from.  Consequently I have come up with the notion that it is approximately 2 thou change in points gap = 1 crank degree, or one flat on the screw = 2 crank degrees.  I attach my calculations for critique by the experts.  This is very provisional as I don't have a good vernier to make accurate measurements or a dial gauge to see what happens in practice.  I hope it is 'right ballparkish' though. If anyone can 'tighten this up' with better input data, then I can modify the calcs accordingly. Better still if those with dial gauges and dexterity with feeler gauges could confirm empirically.

[chaterlea25]

Hi All,
Yes Stu's  method will work, without a battery
BUT!! the connections have to be soldered to the slipring not pushed in
the slipring now has to carry current (not much voltage) also the brushes need to have neglibile resistance
This modified system works on the energy transfer method. You need 2 coils, they have to be AC types
(old honda 50 or italian scooter)
I sucessfully even got a V twin BSA to go on this system,
My brothers early Rudge which ran the mag at engine speed (originally maglita) ran on a conversion like this for years and years
This was back in the days when it was virtually impossible to get a mag rewound at a reasonable cost

HTH
JOhn O R