BSA Pre unit A7 A10 - Electrics & Ignition


  • Magneto rebuilds
  • Electronic Ignition conversion kits K2F & K2FC twins
  • Dynamo rebuilds
  • Electronic  DC regulators  6V / 12V
  • LED & Low wattage bulbs
  • Alternators & Rotors
  • AC regulators single / three phase
  • Timing kits
  • Special ignition prototypes
  • Electrical fault finding




We specialise in the renovation of the LUCAS K2F and K2FC magneto as fitted to BSA,TRIUMPH and NORTON twins.
The most common problem with original magnetos is failure once hot. The engine will start from cold
Then run for a short while, a misfire will develop and the engine will finally stop. Once the engine is cold again the engine will start. This is usually due to a breakdown in the insulation of the condenser or of the armature windings themselves.

When we undertake renovation of these magnetos we examine the following:-
•    Mechanical - Bearings, insulation, washers and shimming the armature
•    Electrical - Armature windings, Condenser, Slip ring, Points and Bushes
•    Magnetic - Check magnetism and Remagnetise magneto body
•    Ignition - Check Spark strength, Spark timing and stability

We use the CRYPTON MAGMASTER (from the 1950s) to do a comprehensive testing programme on each magneto we rebuild. This allows us to do slight adjustments to the magneto to achieve the best constant and accurately timed spark that the magneto is able to produce.

The final 20 minute hot running test programme includes:-
•    Checking the normal spark HT Voltage;
•    Checking the maximum available spark HT Voltage;
•    Checking the ignition timing stability over rev range;
•    Checking the ignition timing for correct timing angle (for most twins this is 180 degrees);

By performing this test programme we can be confident that the magneto you fit to your engine will be at peak performance and will remain reliable for years to come
Send your magneto to us, we will test it to ascertain its’ faults, provide an estimate and contact you to discuss the work required.

Each Renovated magneto is backed by our 2 year guarantee.

Have you considered replacing the magneto with an electronic ignition?

This kit is designed to fit inside your original Magneto body without having to do any modifications to the body, and to give the appearance that Magneto is standard , kit is a very low power consumption using only 6 watts of power when running, so suitable for use with a dynamo that only gives 60 watts maximum power, kit runs on 12v , can be used as negative or positive earth, it is easy to convert original 6 volt Dynamo by fitting a 6 to 12v regulator box converter, 12v battery and bulbs. Kit comes with ignition coil, modified pickups, wiring, on/off switch, main module that fits inside magneto body, and fitting instructions. A fixed magneto drive gear will be required , as the advance and retard ignition advance is controlled electronically.




At SRM we specialise in the renovation of these particular models of LUCAS dynamos.
In the 1940s the LUCAS E3H (40 Watt) unit was used extensively on a variety of British single cylinder engines later to be replaced by the more powerful LUCAS E3L (60 Watt).

The E3L dynamo was used on many British twins such as the BSA A10, TRIUMPH T100,T110 and NORTON DOMINATOR.
The design of this dynamo is the same throughout the range but different drive shafts are used for different models.

Each dynamo is tested on the CRYPTON ELECTRICAL TEST BENCH to determine its condition and an estimate of the cost to renovate the unit is produced.

If the dynamo was to be fully restored a new armature and field coil would be fitted together with new bearings. The outer body would be Nickel plated and the alloy ends bead blasted. New brushes would be fitted and then the dynamo would be thoroughly tested.
Firstly the dynamo is wired for a ‘motor’ test - this runs the dynamo as a motor, the motoring speed is checked as is the polarity and rotation. This test also polarises the magnetic field in the field coil core;
The dynamo is then fitted to the CRYPTON ELECTRICAL TEST BENCH to be driven as if the dynamo were fitted to the engine. This test confirms the dynamo will charge when fitted to the engine and in the correct polarity for the earthing system on the bike.

Each Renovated dynamo is backed by a 2 year guarantee.

CONVERTING FROM 6 Volt to 12 Volt SYSTEM            

We have that the most reliable way to convert to 12 volt is to leave the dynamo at 6 volt and use an electronic regulator box (DVR2 type) in conjunction with the SRM dynamo belt drive. The dynamo belt drive is geared so as to speed up the dynamo relative to the engine and so produce more voltage. The system would charge at around 1400 - 1500 rpm and reliabily produce 60 Watts.  We would also use a 35W/35WW Halogen headlamp bulb (as bright as a 50W/50WW stadard bulb) and an LED rear lamp to conserve power.  


SRM produce our own toothed belt dynamo drive for the BSA A10 and A7 engine


An alternative is to fit the ALTON alternator. This is a small powerful alternator condensed into the size of a dynamo. It is a direct replacement and comes with a Vbelt drive and a 12v rectifier / regulator box.

Please contact us for prices.