E: Engine My BT-H Is Not Providing Spark

[CarlHungness]

I have a BTH that was bought around 2006/07. At first it was great but during a very wet ride to the Scottish Applecross rally in 2009 the bike got harder to start but once started ran fine and this is a bike that I have done thousands of miles on over 30 years and is usually a 1 or 2 kick starter. Eventually the BTH failed and refused all efforts to start but there was still a visible spark at the plugs. I replaced the HT coils and leads and rechecked the static timing it made no difference so removed the BTH and returned it to the the manufacturer at the time which in 2009 was different to the guy who makes them today. At the same time I refitted the old points /coil ignition unit and suprise the bike started first kick which to me proved the BTH was the problem. The unit was returned to me with a note saying there was no problems with it so I refitted it and went back to virtually impossible starting. So the BTH was thrown on the shelf in disgust and the bike has successfully run on the old points ignition since them.

So I have just dug out the old BTH from the back of the workshop and opened it up. First thing was I removed the small cover off the end which has BTH engraved into it and I was suprised to find 9 threaded holes in the end of the main cover but the smaller BTH cover only uses 3 of those. There was no sealing of the smaller cover to the unit and no sealing of the unused holes so an easy path for water to get in. I then removed the main larger body cover which again had no gasket or sealing at all. The two screws which hold the pickup coils are rusty and the magnet in the rotating arm has loose rust particles magnetically attached to it and when rotated to line up with the picup coils the rust particles bridge the air gap and this will result in a varying timing and is probably the cause of my problems. I may de-rust these pickup areas sometime and try the BTH on a bike againg but the Rapide is running fine so I'm loathed to start messing with it.

Please note BTH is now owned by a different person and I believe he doesn't service devices made under the previous owner, but you would need to check that. I have no experience as to how they are assembled today.

These photos were taken today:

View attachment 59475View attachment 59476


View attachment 59477

What coil/ignition system do you use now? I have an original mag, rebuilt and never used, but I'll consider
something else if B-TH won't service my unit.

 

[Simon Dinsdale]

What coil/ignition system do you use now? I have an original mag, rebuilt and never used, but I'll consider
something else if B-TH won't service my unit.

It’s a unit I made myself 30 years ago.

 

[CarlHungness]

It’s a unit I made myself 30 years ago.

That's wonderful, sure glad to hear it's working well.

 

[BigEd]

I've never heard of a B-TH 'going bad', so I may have set a precedent.

Upon inspection I DID find oil had seeped down a plug wire, through the now supple spark wire caps and into the bottom where the wire attaches to the coil(s). So I thought oil on a plug wire was my problem.
I ordered new coils and wire and paid very close attention, I hope, as to how to unhook the old and install the new without mixing up the wires.
Just tried to start the bike, and seemingly not getting any spark. All alone I can kick the machine over with no plugs and hold a spark plug to the head. I have a center stand now that allows me to stand next to the machine and kick it through. I've held the plug to the head, put my finger on the electrode(s) and no spark. I tried both plugs and am sure they were grounded as I kicked. I've done this previously years ago with a helper and did get spark
Suggestions?

I just don't have enough knowledge to know how to test the BT-H, so need some assistance.
Thanks in advance.
Best,
Carl Hungness

See if you can check continuity with a multimeter from the wire end to a tab on the coil. When you fitted the new HT leads to the new coils did you check that the spike or screw thread in the nose of the coil actually went into the wire? It is possible to miss the wire and screw into the insulation of the HT cable. Poking the point of a scriber into the wire to make a bit of a pilot helps. See if you can check continuity with a multimeter from wire end to tab on the coil.

 

[Chris Launders]

Before doing anything else cut the cutout wire near the unit and isolate it, no-one has mentioned this but if there's a short on this it will obviously stop it from sparking
It seems strange you cannot get at least one spark out of it, the systems inside are separate for each cylinder, I think you should be able to do quite a bit of detective work yourself.
Take it off and mount it in a vice so you can spin it with a tap wrench or battery powered drill
The unit consists of a generator and two CDI units, so having made sure there's no rust or corrosion you should be able to find the wires from the generator and see if spinning it you get an output.
If you have then try a meter across the connections for the coils and again spin it, also check the gap between the rotor and the pickup coil ends, this should be minimal.

 

[CarlHungness]

Before doing anything else cut the cutout wire near the unit and isolate it, no-one has mentioned this but if there's a short on this it will obviously stop it from sparking
It seems strange you cannot get at least one spark out of it, the systems inside are separate for each cylinder, I think you should be able to do quite a bit of detective work yourself.
Take it off and mount it in a vice so you can spin it with a tap wrench or battery powered drill
The unit consists of a generator and two CDI units, so having made sure there's no rust or corrosion you should be able to find the wires from the generator and see if spinning it you get an output.
If you have then try a meter across the connections for the coils and again spin it, also check the gap between the rotor and the pickup coil ends, this should be minimal.

Now I'm mixed up..the mag is off the bike...if I am LOOKING at the shaft, pointing at my nose, which direction do
I spin it to check it. This is frustrating as hell. Of course I isolated the cut out wire, and have kicked it until I
was blue in the face and got no spark from either plug...I held the damn leads with my hand against the heads,
and no spark. Thanks.

 

[ClassicBiker]

Carl,
I snagged the gear train from thevincent.com. With the shaft of the mag pointing at your nose as you describe turn it clock wise and you will replicate the rotation as if in the engine.
Steven

 

[CarlHungness]

That's what I thought but oh, how to make sure. It sure is lovely to have folks out there
so willing to help. My many thanks. Will go see an electronics friend who can
definitively tell is she's sparkin'.

 

[Simon Dinsdale]

Carl
Sorry it may sound like a stupid question but was the BTH actually rotating when you kicked the engine over? Just wondering if there a few stripped teeth on the mag gear as it still uses a fibre or plastic drive gear in the timing side area.

 

[oexing]

Just thinking, do electronic CDI "magnetos" need an internal timing for generating high voltage ? My knowledge about these is minimal, thinking they just charge a capacitor while in rotation. That cap will be discharged at ignition position later , so is an internal timing essential on them ?

Vic