Misc: Ignition BTH Magneto ground wire issues

[craig]

I have owned (and still do) several BTH ignition systems, single and twin, early BTH and later BTH.
For some reason none of my BTH systems are in service on Vincents, simply sitting in boxes.
My mind is a little cloudy now after a few years of running and maintaining Norton P11 and Commandos.
By the way , I have converted 4 Norton to Tri Spark that we ride several days a week with no issues for years.

So now I am trying to remember why I pulled this BTH 0810AR94S off the Comet and went back to Lucas OEM mag.
I think it might have been hard starting and weak spark, but there was discussion on "grounding" wire.
This BTH has a single , thin, unshielded ground wire.



Some fix involving running the ground wire to the rear, under the engine, wrapping it around the rear axle three times installing a kill button on the rear fender.
Maybe I don't recall exactly.

So years go by, I get a twin running , and order another BTH, figuring BTH things had gotten to a higher standard, and all of the happiness reported here on forum.
This BTH is also in a box with the twin running a stock Lucas magneto. I don't recall the issue but some perceived problem.
This twin BTH magneto has a "shielded" ground wire.



My question is - with this early BTH now reinstalled on the Comet and the fact that the Comet starts fairly easily today,
What is/was the fix for this earlier single thin unshielded ground wire??
I would prefer to have a kill button on the handle bar.
Does a shielded wire solve any issues that you have personally experienced?
can a shielded wire be retro installed easily?
do you have to cut off this kill wire and not have handle bar kill?
interference at various engine speeds with Podtronics regulator?

Thank you for valuable input on this ground wire issue.

 

[ClassicBiker]

My twin is running on a used BTH with a thin un-shielded kill wire. From what I remember is folks were having trouble because they were running the grounding wire along the spark plug wire or very near it. Thus giving a false signal of some sort. My coils are mounted to a bracket fixed to the mag cover not under the BTH. This way the spark plug wires and the kill wire are no where near each other. Mine emerges from a small hole at the rear of the mag cover and is folded over on its self and wrapped in electrical tape. I don't use. Others on here have advocated for cutting the wire off as close the body of the BTH as possible. I have my throttle stop screws set so that closing the throttle right down shuts off the engine. I have a light friction on the throttle to allow it to idle at what ever speed I desire. As there is always tension on the cables I know the slides are moving together and checking both carbs with a vacuum gauge shows they have the same draw, so they are synced.
The holes in the mag cover are the result of where I mounted the coil for the Lucas Rita when that was fitted.

 

[craig]

My twin is running on a used BTH with a thin un-shielded kill wire.

Did your bike have an issue with the thin kill wire which caused you wrap it up and stow it?

I have moved the single coil down and away.

 

[ClassicBiker]

No I didn't have the issue. I decided I would avoid the issue by not using the kill wire. Though I have been considering seeing if careful routing would allow use without issues.
Steven

 

[Robert Watson]

I have said this before. I have a BT-H on my Black B, the kill wire is zip tied to the HT leads, has been from day one. Probably 15 or 20 K miles that way, only time it has had a misfire was from A) HT leads rubbing on hot fins and burning through to the wire, and B) one HT lead working loose and almost falling out of the coils so that the spark needed to jump a gap of about 3/8" to reach the HT lead.

Maybe I'm just lucky

 

[craig]

I have a BT-H on my Black B, the kill wire is zip tied to the HT leads, has been from day one.

Is your BTH kill wire shielded or the early thin wire ?

 

[Robert Watson]

Early thin plain wire.

 

[davidd]

Robert,

I am not certain, but I think the problem was caused by running the power wire and the ground wire together. There was some "cross-talk" that caused the power wire to ground.

I ran the thin, single kill wire to my kill switch, but it was well-separated from all other wires. I never had a problem except that my BTH would not ground to the engine. I had to run a separate ground from the body of the BTH to a nut on the crankcase. The problem did go away and I believe it was caused by some sealant on the crankcase hole, although I did not see any.

Jim Young had a shielded ground on his twin and cut it to prevent a problem, which caused a problem when it got clamped hard in the mag cowl and grounded.

You can get wire shielding to slip on over your wire. It is used on small aircraft and is available. There are some ignitions that need a Faraday cage to work properly. When running unshielded the ignition, it will shut off a nearby ignition if it creates a certain RFI. Thus, the entire ignition, plug, and wires are shielded and grounded to the battery to prevent other bikes from shutting down your ignition.

Because you do not seem to need shielding, I think a single unshielded wire installed in a segregated manner would suit you fine.

David

 

[Robert Watson]

David, What power wire? do you mean the HT or are you thinking the coils are mounted somewhere besides under the cowl? This is a new style BT-H self powered CDI ignition. Only 3 wires coming out from under the mag where the coils are, all zip tied together and not been a problem except as noted above in many miles!

 

[GBewley]

i too have run BTHs for at least a couple decades, and the first still in place, unshielded wire running alongside the HT leads. Never the first problem. I recently installed a new BTH on a customer bike and the kill wire was not shielded. I spoke to Peter Nugent who told me more people were having trouble trimming and installing the shielded ones than ever had problems with the unshielded ones so he reverted to the original design. I have run both types with no issues.

FWIW, one thing I do is always install a bullet connector in the kill switch wire, this placed so it can be tucked into the space between the oil tank proper and the headstock. This way if I’m questioning my ignition I can pull the bullet connector out upwardly to disconnect (bullet from switch side being pulled out and leaving the magneto end shielded by the bullet connector) and eliminate the ground/switch as a possible problem without disassembling the switch or removing the mag cowl.