Twin coil

[Howard]

Just a thought from the weekend - I've been working on the bike and my brain (such as it is) starts to go off at a tangent when I'm doing mundane tasks like paint stripping and polishing.

Has anyone tried fitting a twin with a single coil with twin outputs? ie Two sets of points switching one coil with two plug leads.

Seems common on parallel twins and In-line fours.

As I see it there will be an extra spark on the non firing cylinder somewhere with the exhaust open or with both valves open. I can't see this will cause a problem, and I could hide a modern single coil easily under the mag cover.

Could I try this by connecting my two Lucas coils to both sets of points?

 

[Robert Watson]

There are many twins running single coils with twin outputs and a lost spark, however they are usually fired by electronic systems. I have run both Lucas Rita and for many years the dreaded Harley Davidson gear. HD have proved to be very reliable, the only failure I know of being from high tension leads failing, but that's what you get for putting used ones on and then driving it for 40,000 miles!

 

[Pete Appleton]

Wasted spark

A single coil with two outputs is used on many vehicles that have electronic ignition. This system is called 'wasted spark' for obvious reasons.

On an in-line engine the wasted spark occurs on the other cylinder just as the inlet valve is about to open for the overlap period. On a 'V' twin the wasted spark from the firing of the front cylinder occurs 20 degrees or so into the induction stroke of the rear cylinder with the inlet valve well open. You might think that this would cause a pop back through the carb, but it doesn't. The Pazone and Boyer Bransden electronic ignitions supplied for Vincents use wasted spark with no ill effects.

The only thing to watch out for is that you don't fit a coil intended for electronic ignition to a contact breaker system as they are very low resistance (typically less than 0.5 Ohms) This will melt the contact breakers and the long 'points closed' periods will destroy the coil within seconds. For contact breaker type systems you will need a coil of about 5 Ohms.

The idea of using twin points may need some careful thought as you will have to ensure that there is at least one set of points open at all times or you won't get it to fire when you want it to

 

[Howard]

The idea of using twin points may need some careful thought as you will have to ensure that there is at least one set of points open at all times or you won't get it to fire when you want it to[/QUOTE]

This is one I hadn't thought of, but don't you mean always one set closed? I'll have to think this one through a bit more.

 

[Pete Appleton]

twin points

No I do mean one set always open, although you have got me doubting myself.

The coil sparks as you break the earth connection on the low tension lead. With two sets of point in parallel if one is always closed then the circuit is never broken and you don't get a spark. so one set must be open and when the second set breaks this is when you get your spark.

Another thought is that you may have to remove one condenser.

 

[Howard]

This is getting very complicated. I'll sit down and think it through with a pint later.

 

[Robert Watson]

One local bike has twin points. Last year after installing new points, a few hundred miles later it went on to one pot. All the experts and a whole day later there was no improvement. The following day the point gaps were opened up and presto, two cylinders. The new points had lousy wear blocks and they wore down very quickly. One set of points must be open at all times or no sparks on one pot.

Robert

 

[Howard]

Thanks Robert.

I'll stick to 2 coils for now. I know it runs OK, and I can put it down as one of the things I can develop later.

I think a lot of things have passed me by while the Egli's been off the road, I'm trying to catch up with electric starts, LED bulbs, Alton generators etc

Regards

Howard

 

[Howard]

Sorry, thanks to Pete too, I hadn't realised it was a threeway conversation.

 

[Len Matthews]

Twin Lead Coils

I've been running my outfit for years using a Series D distributor minus original cap(replaced with cap from BSA C10) and rotor arm in conjunction with an H-D coil. This set up has been totally reliable an easy to service.