Misc: Ignition B.T.H Mag - no spark

[greg brillus]

I have struck it several times, the pinion nut does not pull the taper up tight.........It basically becomes shank bound before the taper bites home. You can do one of 2 things.......Either machine a small amount off the inner face of the nut so it can screw on a bit further, or disassemble the 4 small screws that hold the pinion assembly together and install a washer between the face of the center nut and the inner drive boss, this will space the two apart enough that it pulls on to the taper enough to clamp it. You could do a simple trial fit first before assembling the pinion completely.........There is you issue, all good.

 

[Martyn Goodwin]

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.

please confirm - when you kick the motor over does the drive pinion rotate, that's the pinion or gear attached to the magneto , inside the timing case (there is a small cover over this that you can remove, just 6 screws). If that's NOT moving then neither is the magneto mechanism and then no way will you get a spark.

 

[van drenth]

Most probely you have the coils wired up wrongly.
van Drenth JC

 

[greg brillus]

Read carefully the last sentence from Paulc post number 4 above........ That description says it all.

 

[vibrac]

Check you have clearence between back of ATD and crankcase wall Ben had just this trouble last week on a customers bike not used for 40 years it just needed a few thou off the back heads and the tapers engaged fully

 

[Ian Savage]

Paul, did you resolve the problem?

 

[Ken Tidswell]

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

i suggest you take off the timing cover and the drive pinion and the mag and assemble it on the bench you can then see if the drive is properly engaged with the mag , and then do somrthing about it. My experience with the modern BTH is that although the voltage at the plug is far higher, a rebuilt Lucas mag gives a ' fat' spark of about 11/4 amperes. usually my Comet started first kick with Mr Lucas and took any number with a new BTH. And then i could give a really fast kick. As has been suggested the coils may be suspect. A local owner with a twin had the same problem , It would start hot but he lived half way up a hill which came in handy when starting from cold. Every Vincent owner should live at the top of a hill, sorry to be so fippant but you are not the only one one who has a problem with a BTH mag seemingly. it is not the magic remedy it ought to be

 

[Robert Watson]

I have found that a cold BT-H will have a hard time firing an NGK of a 7 range, but will fire a 6 much easier.

My Black B was a bear to start on B7ES as was a big bore Comet. Swap them to B6ES and pretty much will start on one or two kicks.

 

[mercurycrest]

Another problem that can occur with modern BTH's, is the kill wire is a coax cable and can accidentally ground it's self out.

 

[Robert Watson]

The only 2 BT-H's I have worked on have a plain black wire with copper core and plastic coating. Mine has always been clipped to the HT leads and never shorted them out.