The following might be a useful guide to start to understand the various variants available:
Alternator types (using the LU54202299, 74 mm rotor). This rotor is RM20 and is 1 3/8" thick.
RM20 rotor is used with all stators RM19 and up.
47149 (RM15) Energy Transfer 5 wire batteryless ignition version used on T20, T100,
T120, TR5, TR6, A65, C15 etc.
47204 (RM19) 6 V, 3 wire 120W single phase replacement. Fully encapsulated, highest
output 3 wire, 6 volt unit.
47205 (RM21) 2 wire 10 amp, 120W single phase this unit can be regulated to 6 or 12
volts and is a popular replacement for the RM19. A solid state regulator must be used with
this unit if it is being used to supply 6 volts.
47239 (RM27) 12V, 2 lead single phase 16 amp. Improved output over the RM21.
Recommend 12v single phase unit, can be used with a capacitor (battery
47252 (RM24) 12V 3 phase 3 lead, 3 phase 10.5 amp stator.
Fitted originally as standard to Triumph T140 pre electric start models (from 1979).
47244 High output RM24.12 V, 3 wire 180W 3-phase. A very popular and reliable upgrade
of the electrical system. It can replace all above stators, not only producing more
maximum power but importantly producing more power in the lower rev range.
Adjusting running clearance
When mounted to the engine there must be a minimum 0.2 mm (0.008”) clearance
between the rotor and stator all the way round. Less and the rotor may touch the stator as
it heats up. If this happens the stator will overheat due to friction and fail very quickly, this
type of failure is not covered by the warranty. Inspect the pole pieces and the rotor for
signs of touching after initial fitting. The clearance is adjusted by slightly loosening the
mounting bolts and - carefully - tapping the stator with a soft faced hammer then retightening.
NOTE: Some Triumph T20s have a taper on the crank, in order to fit the 74 mm rotor you
will need to have an adaptor sleeve machined. T20SM models have a parallel fitting on the
crank. When ordering for Triumph Cubs please check the crank for a 19 mm parallel fitting.Lucas
is a registered trademark of Lucas
©Rex’s Speed Shop 2018. All rights reserved. Rex’s British Alternator Info Rev 3 nov 2018