Thorspark Electronic Ignition on a VH

[Bob.Murphy]

I've been playing about with my 'VH' again . . .

After fixing the tank, machining the barrel top face to fit the head without a copper gasket and fitting a 7.5:1 piston I had it running with a re-built MO1 Mag that had a 'Brightspark' condenser. The Dynamo is now running at 12 volts and the bike has been re-wired Negative Earth with a "Dynamo Regulators Ltd DVR2" Regulator. It has LED bulbs.

I had it running but starting wasn't good. When it ran it felt good with plenty of poke. It has a 28mm Concentric with a 200 main jet.

Then I stripped the Concentric down, put it through my Ultrasonic Cleaner and re-built it with some new parts and gaskets. At the same time I removed the points assembly from the Mag and fitted a 'Thorspark' Electronic Ignition System (it has a coil and a keyed ignition switch but still uses the manual advance/retard).

The 'Thorspark' set-up has an alloy rotor in place of the points assembly and a solid-state pick-up mounted where the face cam fits. The rotor has two magnets (?) at 180 degrees - presumably for balance. This will produce a 'lost spark' on the exhaust stroke.

Timing is a bit hit-and-miss. There is a felt pen mark on the static part and this is aligned with a magnet on the rotor when at full advance with the piston 5/8" before TDC on the compression stroke. so far so good.

On starting, the exhaust note is extremely loud, it won't run cleanly or tick-over (despite playing with the throttle stop, air jet and the height of the jet needle) but it feels to have great potential. A neighbour, who has the same Thorspark set-up on his 3GL Matchless, is saying "There's something not right there, but I can't decide what" .

I have adjusted the timing (by rotating the rotor a little at a time) but it doesn't improve. I'm now thinking that the lost spark is the problem and its that which is causing the very loud exhaust (the basic motor hasn't changed since moving from Mag to Coil ignition).

My next step is to rotate the rotor 180 degrees in case the magnet polarity is critical. The little magnets may well have he same polarity as they are set axially in the rotor, so this may be a waste of time. Removing one may be the solution.

Has anyone else been here and have any pointers (apart from "leave the B thing alone, Ariels knew what they were doing" )?

Bob (striving for perfection).

[nevhunter]

bob, the usual cause of a very loud exhaust (Muffler not having been altered ) is retarded ignition or advanced cam timing. Ie exhaust opening early The wasted spark is not a good thing as it can make a flooded engine catch fire more easily when you are starting it.
. The dead spark cannot cause the effect you are getting but could cause an intermittent loud backfire (explosion in the muffler) if you have a very crook plug. It's a common feature of many coil ignition systems on 4 cylinder motors where you run 2 coils for 4 cylinders and no distributor Distributors are pretty much absent from modern motorcycle engines. Your split slip ring is a distributor in twins with maggys Nev

[Bob.Murphy]

Thanks Nev. I had thought about retarded ignition but the bike kicks back when starting. On two occasions it has kicked back and then run - which is probably a symptom of the lost spark.

I have never investigated the valve timing since acquiring the bike back in 2013, I have assumed it was standard as it seemed to run OK (but disappointingly slow) when it was going - starting became an increasing problem hence the work on the Mag and the trial move to coil ignition. I intend to ride long distances and British Motorways, in the rain, with heavy traffic is no place for a dodgy spark or a failed dynamo!

It has always had a fair 'bark' when under load. The silencer looks standard and is an "Ariel Motors" one - made by the Club some years ago. It may be just an empty can, I don't know! I'll need to check it out.

My main problem is that I have too many variables, its never a good idea to change three critical items at the same time (compression ratio, Carburettor & Ignition System) so its a matter of eliminating potential problems one at a time.

Bob.

[will_curry]

My Thorspark purchased last year has only one magnet.

I've not fitted it yet so I can't help with how it works but I've just seen in the Thorspark
notes that the second magnet shouldn't be removed. Another challenge.

I bought the Thorspark for much the same reason as you having had a magneto fail catastrophically
when the slip ring broke up. Especially annoying as the slip ring was replaced when the magneto was
refurbished not 10 years ago.

[Bob.Murphy]

That's very interesting, Will - thanks for that.

I re-read the Thorspark fitting instructions and it definitely says (not verbatim) "The magnetic trigger for a single cylinder motor has two magnets, do not remove one of them".

I wonder if it is for balance, in which case replacing it with a piece of mild steel might be OK ?? On the other hand it may be a polarity issue.

Next consideration . .

The fitting instructions say "set the piston to 5/8" before TDC on the compression stroke with the ignition at full advance and then set the rotor such that the magnet marked with a felt pen is adjacent to the felt pen line on the solid state trigger unit".

The problem here is that I don't have a felt pen mark on the rotor so don't know which magnet to use. Maybe it doesn't matter, but I think it does as the Instructions go on to say:

"Test the timing with a strobe" (it describes how to set up a timing disc and pointer etc) "you will see one bright light and one dimmer light, ignore the dim light".

I assume the dim light from the strobe is the 'lost spark' on the exhaust stroke, which means that the magnet polarity matters.

This afternoon I went back over the settings. The exhaust tappet was a bit tight so I reset it. I put the jet needle back in the middle groove as it was worse when in the lowest setting (highest groove), made sure that there was slack in the throttle cable so that the slider bottoms-out properly, I marked the magnets on the rotor blue and red. I was running on red so rotated it 180 degrees to give blue a try.

What I really need is a small magnetic compass to see if the magnets really are different, which brings another conundrum . . .

The red tip of a compass needle points to Magnetic North which is a few degrees off Geographical North (and fluctuating), but is the Earth's North Pole N or S (i.e. is the North compass needle actually a S pole) ?? . . . So many problems .

Once I have worked out which magnet works best I'll remove the other one and see how the bike runs. To do this I may have to examine my neighbour's 3GL Matchless .

Bob.

[will_curry]

Bob,

Try 'phoning them. They were very helpful when I couldn't make the backplate fit.

I'm not sure it actually matters which polarity is which. What matters is if they are the same
or different.

I'd wondered about balance. If I get some free time I'll experiment tomorrow. I have a
spare magneto in bits at the moment to play with.

Will.

[will_curry]

Bob,

Just found a compass - the outer face of the single magnet is North and the inner South.

By North I mean that the part of the compass which points North - Bedford in my case - points
to the outer face and the part of the compass which points South - Luton ditto - points
to the inner face.

Will.

[Bob.Murphy]

Thanks Will,

I need to find a compass and see if both magnets are oriented the same way. If not I'll use the one with the outer end that the North needle points to for the trigger.

BUT:

I wonder if Thorspark intended your rotor to only have one magnet (I can't see anything apart from friction holding it in). Did you query it ??

Maybe you are missing one (which negates the above test) .

Life just gets too complicated .

Bob.

[alan.moore]

Bob,
Could you test the polarity with a small bar magnet, if the magnets in the rotor attract the same end of the bar magnet they have the same polarity pointing outwards.
As you say the fact that Thorspark say you get a strong flash and a weak flash from the strobe light would suggest there is a difference in the magnets but the question is which one to use

Cheers
Alan

[roger.fellows]

When the Earth's polarity flips - which is supposed to happen from time to time - it probably won't matter a lot to any of us.