New style BT-H mag

[Hugo Myatt]

I replaced everything you could think of, poor wire, mis threaded wire, poor kill button, bad plugs, rebore engine for fresh compression, new rings for least oiling, new plug cap,

Yes I dont see replaced coil in that list.

I don't have personal experience of this but others do. I am told that the early coils could fail unexpectedly. What symptoms they displayed in failing I do not know. It seems that a 'new and improved' coil is now supplied.

 

[craig]

I borrowed Lucas magneto, the problem Comet ran 100+ miles with no problems - used same plug wire, cap, sparkplug, kill button, etc, - only changed mag and ATD.
So my new BTH has a problem when brought up to normal operating temperature. i believe these are factory tested at ambient temp

I have had nothing but problems with my new Comet BTH since day one. Bike runs fine for 30-40 miles then total loss of spark. After it cools down for several hours, the spark returns...........by then ..............several times you have trouble shot and replaced everything you could think of, poor wire, mis threaded wire, poor kill button, bad plugs, rebore engine for fresh compression, new rings for least oiling, new plug cap, send unit to England to be told there is nothing wrong with BTH, reinstall ....run 20 miles then total loss of spark....cools down, spark returns.
I am planning on borrowing a standard Lucas magneto to see if a standard mag will run as required.
I am hoping BTH can provide a good solution as well.
This Comet has been stranded 6-7 times for this BTH.
I have ridden a standard Comet for thousands of miles during this same time. The owner is reluctant to let me pull the Lucas to trial on mine, but in just a few days.....

 

[vibrac]

So my new BTH has a problem when brought up to normal operating temperature.

Or the coils...

My point is the coil or coils (I have twin spark) are small, they cost relatively little, postage cost is low compared to the unit. try new coils then if it persists then is the time to remove the BT-H and get it checked

Nb I just had mine checked the test is impressive

 

[Phil Mahood]

s there a standard coil that can be sourced other than from BT-H?

 

[craig]

How were the secondary coils individually checked off the magneto?
What acceptable parameters were found when these were checked?
To what temperature were the coils heated to achieve normal operating conditions?

My point is, my BTH system was checked by BTH and returned and continues to fail. I was not impressed with the test.

Or the coils...

My point is the coil or coils (I have twin spark) are small, they cost relatively little, postage cost is low compared to the unit. try new coils then if it persists then is the time to remove the BT-H and get it checked

Nb I just had mine checked the test is impressive

 

[bmetcalf]

Maybe Goffy has one. See http://www.norbsa02.freeuk.com/goffyelectrex.htm scroll halfway down. It doesn't say specifically for BTH.

s there a standard coil that can be sourced other than from BT-H?

 

[davidd]

I have never had a problem with the New BT-H in years of racing. Stock magnetos last a couple of races and need lots of work. I have been very impressed, however, I had to add a ground strap as the standard mounting did not seem to provide a consistent ground. Like Phil, I would love to know if there is a replacement coil from Dyna, PVL, etc.

David

 

[craig]

I ran the Comet another 100+ miles to day with 10+ restarts on first kick........again this is with a stock Lucas magneto rebuild by Doug Wood about 3200 miles ago.
Upon returning, i took a trigger operated heat gun and took readings all over the engine.
Oil about 135F
lower engine 140F
top of head 270F in several spots, but generally 230F
all over Comet non engine chassis parts - 95F
not real scientific, but data
alloy cover over magneto i did not remove and get Lucas temp, but i will next time.

I borrowed Lucas magneto, the problem Comet ran 100+ miles with no problems - used same plug wire, cap, sparkplug, kill button, etc, - only changed mag and ATD.
So my new BTH has a problem when brought up to normal operating temperature. i believe these are factory tested at ambient temp

 

[Phil Mahood]

So far all my customers have had reliable service with BT-H magnetos. In setting them up, only two problems have arisen. Unfortunately either problem can defeat casual users.

The connection between the lead and pin is bad. It is bad for screw-on types or otherwise. The coils and lead barely fit under the magneto cowl. Putting the cowl on often pushes the lead out of contact. Two thind help. First, silicone the boots to the unit. Then I actually lockwire the leads to the coil bracket. It's an old racer trick to hold gas and oil lines. You tightly bind the lead with lockwire using lockwire pliers then pull it into the socket by securing the wire to the bracket. This bodge works and lasts.

And now for something completely differenet - the armature threads are a bit fat. When doing up the 3/8 BSF nut on timing, it may seem that you have brought the fitting onto the taper. It tightens up hard. Alas, on two recent occasions, the lockup was against the threads, not the taper. The pinion turned but but the armature didn't. I have had to chase the armature threads and check them with a nice new 3/8 BSF nut. Now I do this with all BTH mags. I reported this to BT-H but nothing seems to have been done. All new armatures still have threads that are slightly off - just enough to cause problem.

But, ith all this done, the units works very well, to say the least. That said, I have had equal success with Lucas magnetos rebuilt by Doug Wood. My personal B Rapide has a Lucas. It has been a first kick starter and hard runner for years.

It's hard to beat a good mag, Lucas or BTH.

Cheers, Phil

 

[craig]

Thanks Phill and David, I would like to look over the internals of this BTH, what is the proceedure to do so? Are there diagrams or IPB's for these BTH. If you disassemble a Comet BTH is there an advance or other setting that cannot be reset without special equipment? Have you had to replace internals of a BTH? rotor? circuit board?
Thank for your help on this
Craig

So far all my customers have had reliable service with BT-H magnetos. In setting them up, only two problems have arisen. Unfortunately either problem can defeat casual users.

The connection between the lead and pin is bad. It is bad for screw-on types or otherwise. The coils and lead barely fit under the magneto cowl. Putting the cowl on often pushes the lead out of contact. Two thind help. First, silicone the boots to the unit. Then I actually lockwire the leads to the coil bracket. It's an old racer trick to hold gas and oil lines. You tightly bind the lead with lockwire using lockwire pliers then pull it into the socket by securing the wire to the bracket. This bodge works and lasts.

And now for something completely differenet - the armature threads are a bit fat. When doing up the 3/8 BSF nut on timing, it may seem that you have brought the fitting onto the taper. It tightens up hard. Alas, on two recent occasions, the lockup was against the threads, not the taper. The pinion turned but but the armature didn't. I have had to chase the armature threads and check them with a nice new 3/8 BSF nut. Now I do this with all BTH mags. I reported this to BT-H but nothing seems to have been done. All new armatures still have threads that are slightly off - just enough to cause problem.

But, ith all this done, the units works very well, to say the least. That said, I have had equal success with Lucas magnetos rebuilt by Doug Wood. My personal B Rapide has a Lucas. It has been a first kick starter and hard runner for years.

It's hard to beat a good mag, Lucas or BTH.

Cheers, Phil