Oil tap cut-out, coil ignition

[TimK]

Hi Everyone
I've just fitted a Thorspark coil ignition to my 59 GF and am really pleased with the result - much easier starting and smoother running overall.
I have an oil tap that shorted out the magneto when switched off to prevent wet sumping and want to incorporate it into the coil ignition circuit so that it wont work if the tap is in the off position.
The attached photo shows the wiring diagram for the Thorspark ignition and I'm thinking that if I put an extra cable to Earth via the oil tap in the line from the battery to the Ignition Unit (marked Green on the picture) this will achieve what I'm after.
Has anyone done something similar? I know that I could buy a tap designed for coil ignition that lets current pass when open, but I'm reluctant to do that if I can make the present one work.
Cheers
Tim

[BagONails]

Hi Tim, you got me cos I'm bored at home with the 'rona!

Assuming your bike is '+'ve earth putting a connection between it and the '-' ve green wire would amount to a direct short across the battery would it not?

From the diagram it looks to me like you need to break the green wire with a switch operated by the oil tap. Is there a new key operated ignition switch on the bike and is this in the green wire somewhere?  If so then a second switch in series as I have described would be the way to go, how you arrange that is obviously still the question...

Hope this helps, Ian

[muskrat]

G'day Tim.
Is your oil tap switch a simple on/off type switch or a "to ground" type? If it's a simple on/off the power wire to the cdi unit would be my choice. But I'm not a sparky!
Cheers
ps: only 8 weeks till our show.

[Swarfcut]

 The suggested circuit for the Thorspark isolates the battery (non earth) power feed to the unit by means of a suitable single pole switch. Oil tap switches designed to earth the magneto in the "oil off" position are completely at odds with what you are trying to achieve, so on the face of it the two systems will have to remain apart. Wiring the oil  tap switch as  the earth return for the Thorspark would mean plenty of sparks, but no oil if it is just a simple "feed to ground" type.   Not what you want.

 The earth strap specified seems a little bit of overkill, Thorspark reckoned the system would run on dry batteries in case of electrical failure, drawing just milliamps. BSA never considered a fuse necessary, but a fuse of 10-15 Amp capacity from the loom to battery to protect the main system is more than enough,  a 10 Amp in line fuse should just about handle a load of around 60* Watts on a 6 Volt system, so one with a 15 Amp rating gives some reserve. A low value fuse on its own circuit is a good idea to protect the Thorspark electronics. Perhaps under some circumstances eg a poor earth return high currents may be directed via the Thorspark and the need for a good foolproof electrically sound earth connection is what the instructions are trying to convey.

 Swarfy.

 *  Headlight 30W + Tail 6W +Stop 18W + Speedo 3W plus whatever the Horn draws. ref Service Sheet 806.

[Rex]

I recall that the Thorspark-equipped bike I had (I didn't have it long) had a fuse in the Thorspark feed, and it was a lot lower than 15A. No need for any fuse to be rated that high on old British bikes.
As said, a connection to Earth is for a mag-equipped bike only.
For a battery, coil and points bike the switch needs to be closed (passing current)  when the oil tap is open ie passing oil. That way the engine can't be started with the tap in the off position.

[TimK]

Hi Everyone

Thanks for your input - it's an earthing switch that grounds the magneto when the tap is closed so as Ian says it would be a short across the battery when closed. I was going to get around that by putting the tap down line of the ignition switch, which means that it would only be shorting if I turned the ignition on before opening the tap - but on reflection that's still not good.

Swarfy and Rex, there is 2A in-line fuse that was supplied with the Thorspark kit between the battery and ignition unit and I have a 15A fuse in the main loom to protect the rest of the system, so I'm comfortable that it's all well covered in that respect.

I may get around to changing the oil tap to one suitable for points ignition (passing current when open), but in the meantime I'll have to rely on my bright red "Remove Before Flight" tag that I'm putting around the tap when I turn it off at the moment!

Musky - I'll be bringing the Hurricane along to the show (the engine is stamped BSA after all so I don't feel guilty mentioning it here), see you there if not before.

Thanks for your ideas and opinions,

Tim

[Ted_Flash]

Rather than a tag on the tap, I use a piece of wire with a loop at each end - one loop round the kickstart pedal and one over the oil tank filler cap.  This actually prevents starting, not just reminds.

[chaterlea25]

Hi Tim,
A relay with its coil fed from the ignition switch and grounded through the oil tap switch
Use a normally closed contact  to feed to the ignition unit
When energised  the feed to the ignition will be broken
Oil tap on will de energise the relay and power the ignition

John

[BagONails]

Hi Tim,
A relay with its coil fed from the ignition switch and grounded through the oil tap switch
Use a normally closed contact  to feed to the ignition unit
When energised  the feed to the ignition will be broken
Oil tap on will de energise the relay and power the ignition

John

That's clever, neat solution, I like it! 

[TimK]

Hi Tim,
A relay with its coil fed from the ignition switch and grounded through the oil tap switch
Use a normally closed contact  to feed to the ignition unit
When energised  the feed to the ignition will be broken
Oil tap on will de energise the relay and power the ignition

John

That's clever, neat solution, I like it! 

Seconded - a relay will be a lot cheaper than a new tap, I'll give that a go.

Thanks John

Tim

[fffcycles]

Relay will be a constant load on the battery. Not much to be sure but if you don’t ride much then eventually the protection will be gone. Just mentioning because it is worth thinking about. I have a friend who just pulls the plug caps off and when the tap is turned on he refits the caps and off he goes.
Frank

[Triton Thrasher]

Relay will be a constant load on the battery.
Frank

Only when the ignition is switched on.

[Swarfcut]

 TimK nailed it, on CJ's observation. The NC contact on the relay will be "Normally Closed" when the relay coil is not energised. In other words opening the tap with ignition on allows the relay to drop out and power the Thorspark. From the new ignition switch a nice big red tell tale in parallel with the relay coil is an additional safeguard. Tap Closed, Ignition switch on, warning light on, relay pulled in...no power to Thorspark. Open tap, light off, oil flow and ignition are set to start up.

 Relay coil only draws power with ignition switched on and tap closed, as TT. In my earlier consideration I reckoned to keep oil and electrics apart,  but if a simple circuit as outlined is within reach, all the better. Only proviso is that failure of the relay coil and warning circuit will allow power to the Thorspark with the tap turned to off.

 Ted's double loop trick is a whole lot simpler....

 Swarfy.

[chaterlea25]

Hi All,

The NC contact on the relay will be "Normally Closed" when the relay coil is not energised. In other words opening the tap with ignition on allows the relay to drop out and power the Thorspark.

Yes, that was the way I figured out the circuit design

John

[fffcycles]

True, there will be the ignition switch in the circuit as well so quite suitable really.
Frank