BT-H Magnetos Ltd.

F.A.Q's

A selection of questions we have been asked.

Question:  "Is the new BT-H magneto 6 volt or 12 volt? 

Answer:  Neither.  The new BT-H magneto generates its own power so it doesn't rely on a battery or the bikes  lighting circuit.

Question:  "Will the new BT-H magneto fit my nineteen hundred and frozen to death, XYZ Sport?

Answer:  If your bike originally had a Lucas or BT-H magneto we will almost certainly have a model to fit.

Question:  What is the magneto points gap?

Answer:  The new BT-H magnetos don't have any mechanical contact breaker points.  The spark is triggered electronically so there is nothing to adjust.

Question:  I like spending hours fiddling around trying to adjust contact breaker points  and adjust ignition timing with bits of cigarette paper in inaccessible places.  What am I going to do with my time now that I have fitted my new BT-H magneto?

Answer:  You really do need to get out more.  Try going out for a ride on your bike now that you have got the ignition sorted.

Question:  Can I fit a manual advance lever to my new BT-H magneto?

Answer:  The simple answer is no.  Your new magneto has an automatic electronic advance built in.  You can specify fixed ignition if that is what you prefer.

Question:  How long will I have to wait for my new magneto.

Answer:  We are usually able to supply any of our standard range of magnetos off the shelf.  In the UK we are often able to offer next day delivery if we receive your order early enough in the day. 

Question:  Can I fit my new BT-H magneto myself?

Answer:  If you are comfortable removing, replacing and timing your old magneto you will find fitting your new one easy.

Question:  Will I have to alter my carburettor settings?

Answer:  The carburettor settings on old bikes are often set rich to keep the bike running with old, worn parts or failing magnetos.  Your new BT-H magneto will often fire weaker mixtures which helps your petrol consumption.  If you have fitted a "new" carburettor don't assume that it will be OK because it is "new".

Question:  Will fitting a new BT-H magneto be the end to all my bike troubles?

Answer:  We would like to say yes but realistically there are too many other factors involved.  A correctly fitted new BT-H magneto will solve your ignition problems.  Here is a selection of things that that our magnetos did not solve after customers had finished a bike restoration:  

Tight tappets, exhaust pushrod out, carburettor jets wrong, different length needles in twin carburettors, not enough petrol in the tank, plug leads on the wrong cylinders, timed on the wrong stroke, just simply worn out, ............ 

Question:  Can I use suppressed plug caps on my new BT-H magneto?

Answer:  You can use suppressed plug caps if you wish.  The supplied plug caps are used to give a "period" look.  It is a simple matter for you to unscrew them and fit your own preference.

Question:  What is the advantage of the timing peg?

Answer:  The timing peg allows more accurate static timing as it locks the magneto in the correct fully advanced timing position during installation. 

Question:  There is no spark.  What should I check.

Answer:  Check the spade connections are pushed onto the coil connections and make sure that the high tension lead has not become dislodged from the high tension coil.  The HT lead should be pushed firmly onto the spike inside the coil.   Secure it with silicone sealant or a dab of glue if loose.  A misfire or poor pick-up can also be a sign that the lead is partially dislodged.   Also see the next FAQ's.

Question:  Is there something wrong with my new BT-H magneto as the spark seems very thin?

Answer:  This is normal as the spark from our magnetos is very high tension which produces good performance.  It is sometimes difficult to see the spark at the plug gap, especially in bright light.  Also see the next FAQ.

Question:  How can I easily check that the spark is strong enough?

Answer:  Remove the spark plug and put it back into the plug cap.  Hold the plug by the plug cap or lead to avoid a shock.  Hold the metal body of the plug approximately 1/4" (6mm) away from the engine while you or preferably an assistant turns the engine over.  The spark will jumping the gap from the engine to the plug body and the spark plug gap.  If you can't see a spark because of the light conditions you will almost certainly hear the "crack" of the spark jumping the two gaps.  Practical example.

Question:  Everything seems to be OK on the ignition side but it will not start.?

Answer:  If the ignition side seems OK look at other reasons.  Have you got fuel?  Is the fuel old?  Modern petrol loses the volatile portions if left standing for more than a few weeks.  (Example.)  Try some fresh fuel.  Have you done a rebuild?  What else have you changed?  Valve timing, valve clearance, carburettor, etc.

Question: Do I need to earth the small HT coil to the frame or engine?  

Answer:  No.  One of the connectors on high tension coil provides the earth.  N.B.  The magneto body does need to be earthed if it does not bolt directly to the engine.  On some platform magnetos the unit sits on a separate plate, e.g. Ariel singles.  A layer of thick new paint can insulated the magneto from the engine.  If this is the case put a wire between a magneto fixing bolt and a good engine earth point.

Question:  Will I need to alter the crankcases on my Vincent?

Answer:  On early engines some of the sand cast cases were quite thick.  Some customers have had to relieve the area around the magneto mounting point before fitting.

Question:  Can I use an electronic rev counter with my new BT-H magneto.

Answer:  Several people are successfully using the self-powered Scitsu electronic rev counter.  Nick Brown and Tony Dawson of AJS Motorcycles has sent us this advice.   Scitsu fitment table.

Another rev counter we have successfully tried is sold by Mick Hemmings.  This simply needs a diode (IN4001 or similar) in the sensing lead and a 12 volt supply.

We have tried a Krober rev counter but it did not work.  We have not been able to successfully contact the Krober agent to try and resolve this. 

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Copyright © 2008 E. Grew