I've just fitted a new BTH mag to my Rapide and am experiencing no spark on kick over. I've taken it back to BTH who bench tested it and it was sparking properly but having now refitted it there is still no spark at the plugs and no voltage to the coils on kick over. The cutout black wire has been insulated so it isn't that and the bike has been properly timed. BTH instructions on fitting have been followed to the letter and I am now at a total loss what to do next and so are BTH. The timing pinion with rev counter drive was supplied by Maughan & Sons and all seems fine, i.e. turning on kick over. Has anyone had a similar experience and can advise?
Misc: Ignition B.T.H Mag - no spark
- Thread starter PaulC
- Start date
Breather pinion spinning on it's spindle?
It is only a suggestion, but visually it is very difficult to see the spark emitted from the BTH Magneto, quite different from the big fat blue spark that we are used to seeing from a good Lucas Magneto, I have no idea why this is, but I can say that even if the spark is hard to see, they normally work very well.
Thanks but I have done a multimeter test on the wires to the coil and there is nothing. I'm not sure how the timing pinion drives the mag but I torqued the nut as per instructions and the cogs mesh nicely. I noticed that the pinion nut does not turn on kick over but then I don't know whether it should or not.
I know when I got an early BTH from the original maker Tony Harris the only way we could test it was to place a cigarette paper between the plug electrodes no spark was visible but you could see the burnt holes in the paper afterwards
I suggest you spin the bike up on a roller and then look. I would forget the drive and concentrate on the coils are they the latest version? The older version coil was selling cheaply at Stafford in 2018. Also I cut the cutout wire off there has been reports of interference from the ignition leads
I suggest you spin the bike up on a roller and then look. I would forget the drive and concentrate on the coils are they the latest version? The older version coil was selling cheaply at Stafford in 2018. Also I cut the cutout wire off there has been reports of interference from the ignition leads
Definitely no voltage to the coils (latest versions) and BTH have suggested maybe the timing pinion tapered sleeve is not a close enough fit with the mag spindle so is not driving it. They've never experienced it before but it sounds logical.
"I noticed that the pinion nut does not turn on kick over but then I don't know whether it should or not."
Do you mean the mag drive pinion nut? 'Cos it has to turn otherwise the mag is not rotating.
Do you mean the mag drive pinion nut? 'Cos it has to turn otherwise the mag is not rotating.
With the ATD inspection cover removed you would see very quickly whether the magneto drive pinion was rotating or not, I suppose it is possible for it to loosely grip at kickover speed but not running speed, but to me that does seem a tadge unlikely, as Tim suggested, did BTH test the coils that you are using as well as the magneto.
I doubt you could measure any voltage at the coils with a multimeter on a modern BTH.
The old points type ignition you could place a multimeter across the coil and look for the battery voltage switching as you turned the engine over.
The new BTH is basically a electric ignition and I believe it works on the principle of providing a pulse to the ignition coils and this pulse will be fast rising and fairly narrow in time and also could be over 50V which is why the coils are so small as they are transforming from a higher input voltage. I doubt any multimeter will react quick enough to see such a pulse output from the BTH unit and so you would need an oscilloscope.
I have never seen the wiring diagram of the BTH internal circuit so this is all just speculation and may be wrong.
I suspect the drive pinion is slipping and so not turning the magneto.
Simon