BTH magnetos

methamon

Well Known and Active Forum User
Non-VOC Member
I fitted aBTH to the twin 4 years ago and have nothing but praise. My only concern was the substitution of one mounting stud for an allen bolt - not nice. From memory I avoided this by welding a nut to a socket; using this this required the removal of some metal from the body of the magneto (cant remember quite where) but the casting is very rich anyway.
 

peterg

Well Known and Active Forum User
Non-VOC Member
Howdy Hugo,

There are two variations on the solid drive - which you definitely want rather than retaining the ATD which means buying the BTH with fixed timing forever wedding you to the former - using the same kit. One is a white nylon-ish gear which some claim grows too much with heat causing a lash/mesh issue and the fibre one that looks a lot like the old ATD gear (shiver).

I have one of each on my two installations and Tony's site illustrates exactly what you should purchase. In your case because of location, at VOCS. The fibre one was drilled a tad offset on some holes requiring dressing with a rat tail file to achieve alignment.
 

deejay499

Well Known and Active Forum User
VOC Member
An adaptor is available from the VOCs and probably others and then set up as per series `D`. Straightforward.
 

rapcom

Well Known and Active Forum User
VOC Member
Plastic/Nylon/Tufnol ?

What's wrong with a steel gear? I know it is slightly more noisy, but I like the security of knowing that it will not "grow", will not shed teeth, will not absorb moisture or oil, and with such a light load, will probably never wear out. Just use a cam pinion with a suitable adaptor in the centre.
 

BigEd

Well Known and Active Forum User
VOC Member
VOC Forum Moderator
BT-H Magnetos

The body shape of the BT-H flange fitting magneto enables it to fit on many different makes of bikes. Removing the rear fixing stud and substituting a socket head cap screw was the simplest and most economical way of making it compatible with a Vincent twin.
The need to relieve the casting/magneto body seems to be very random and is not usually a problem. The different thickness of crankcase casting I assume is due to variations you often get with sand castings. The weight of my '48 cases suggests there is certainly plenty of metal and the BT-H magneto went straight on. A "dry" fit first to check clearance after removing the old magneto is a good idea.
A fixed timing pinion (ET48), steel pinion boss (ET223/1), self extracting nut (E54), plus four fixing screws, nuts and washers are required. I got this kit from the VOC Spares Company. If you want to avoid buying more parts you can use an existing mechanical advance/retard pinion with the mechanism "fixed" by welding. [People who have had trouble with mechanical adv/ret mechanisms might suggest blowing up rather than welding up. :) ]
You can see some fitting instructions online at the link below. There are also links to photographs and fitting comments supplied by customers.

http://www.bt-h.biz/vincent_fitting.htm

Eddy
 

block

Forum User
Non-VOC Member
More BT-H praise here

I installed a BT-H on my 1950 C Rapide at the NA VOC Rally. After easy installation (thanks to Neil Donovan and Tim Holcroft for the help and Glenn Shriver for the supervision) the Rapide fired 1st kick. It has transformed my machine (or at least the rider) and brought reliable 1 kick starting cold or hot, as well as stable idle. This all with clapped out carbs. With renewed confidence in my ability to positively start this machine at all times, I feel like I have a new motorcycle. Cheers to the BT-H.
Joe B.
 

mikelmonaghan

New Forum User
Non-VOC Member
BTH Mag

Great! I know how you feel about the starting - I had reached the stage where I prayed that no-one was watching when I started the Rapide - now it just happens.

I take your point about the clapped out carbs - mine are the original 276's and were almost impossible to tune - now I don't know why I fiddled about so much - they just seem to be stable now and I can even run them lean enough to require the air valve from cold.

Happy riding
Mike Monaghan
 
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