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技術: AJS/Matchless Lightweight fitting Boyer Bransden electronic ignition

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A quick and easy guide to fitting a Boyer Bransden electronic ignition system to an AJS or Matchless 250 or 350 Lightweight.

The Wipac ignition system fitted to Lightweights can be improved with a bit of modern technology. While the standard system is OK when in perfect working order, the advance/retard mechanism is prone to wear, replacement points are expensive and the timing seems to flutter all over the place. This leads to erratic idle and poor high-speed performance. The solution is to fit an electronic ignition system that eliminates the points and mechanical advance/retard.

Boyer Bransden make a very neat electronic ignition system for classic motorcycles. This guide describes first how convert an AJS/Matchless Lightweight to 12V and then fit a Boyer Bransden ignition system.

手順 1 Electronic ignition parts  ¶ 

You need convert your bike to 12 volt operation before attempting to fit electronic ignition Boyer don't seem to offer a standard kit for Lightweights, so speak to them first to make sure you get the right parts. The important ones are:

手順 1 Electronic ignition parts  ¶ 

  • You need convert your bike to 12 volt operation before attempting to fit electronic ignition

  • Boyer don't seem to offer a standard kit for Lightweights, so speak to them first to make sure you get the right parts. The important ones are:

  • ROT00111 Rotor AJS/Matchless single

  • STA00156 NT1a 3" stator AJS/Matchless/Jubilee

  • A suitable 12V igniter box (I used a Micro Mk IV for Triumph/BSA singles)

  • In addition to the electronic ignition bits, I'd recommend fitting a new spark plug and suppressor cap (5000 ohms)

手順 2 Modify the rotor bolt  ¶ 

The Boyer comes with two different rotor fixing bolts You need the 26 TPI one The problem here is that both the end of the camshaft  and the rotor have the same thread - so the rotor won't tighten up properly onto the taper (and also makes it difficult set the timing)

手順 2 Modify the rotor bolt  ¶ 

  • The Boyer comes with two different rotor fixing bolts

  • You need the 26 TPI one

  • The problem here is that both the end of the camshaft and the rotor have the same thread - so the rotor won't tighten up properly onto the taper (and also makes it difficult set the timing)

  • The solution is to grind away the first 6.5mm of thread of the retaining bolt to clear the thread in the rotor so it can be tightened up properly onto the taper

  • Cut the bolt to 15mm

  • The thread in the rotor is retained so you can still use a puller to get it off the camshaft

手順 3 Fit the igniter box  ¶ 

Find a suitable place to fit the igniter box and connect the wires according to the instructions

手順 3 Fit the igniter box  ¶ 

  • Find a suitable place to fit the igniter box and connect the wires according to the instructions

  • Fix the box in place with a tie-wrap

  • I used a Triumph/BSA 12V igniter box. Presumably the Norton Jubilee/Navigator 12V one would also work fine.

手順 4 Remove the points and cam  ¶ 

Take off the points cover Remove the points plate screws and lift the plate away Remove the advance/retard mechanism retaining bolt

手順 4 Remove the points and cam  ¶ 

  • Take off the points cover

  • Remove the points plate screws and lift the plate away

  • Remove the advance/retard mechanism retaining bolt

  • To remove the advance/retard mechanism from its taper, you will need a suitable puller

  • You can improvise a slide-hammer puller by using one of the long toolbox cover retaining bolts together with a washer and the heaviest socket you can find

  • Screw the puller bolt into the end of the advance/retard mechanism and use the slide hammer to shock the mechanism off its taper

手順 5 Fit the new rotor & stator  ¶ 

Fit the rotor and retaining bolt. Finger tight is enough, as you will be moving the rotor to set the timing Now is a good time to run the Boyer trigger wires. To make life easier, solder the ends of the trigger wires to the old points wire and pull them through the hole in the crankcase. This is much quicker than taking the outer cover off... The stator plate should fit snugly into the points plate recess

手順 5 Fit the new rotor & stator  ¶ 

  • Fit the rotor and retaining bolt. Finger tight is enough, as you will be moving the rotor to set the timing

  • Now is a good time to run the Boyer trigger wires. To make life easier, solder the ends of the trigger wires to the old points wire and pull them through the hole in the crankcase. This is much quicker than taking the outer cover off...

  • The stator plate should fit snugly into the points plate recess

  • Fasten the stator plate with the two retaining screws - just set it to the middle of the long mounting holes for now.

  • I found the Boyer stator was 0.5mm too large to fit into the points plate recess. If you have the same problem, draw a reference mark around the plate and file away the excess

手順 6 Set the timing  ¶ 

Turn the engine to exactly 1/4" BTDC (or 3/16" BTDC for a late-model CSR with a 9.5:1 piston) on the firing stroke One way to find the right timing position is with a 1/2" socket extension down the plug hole together with a dial gauge. Or you can just mark off a suitable peg in the plug hole.

手順 6 Set the timing  ¶ 

  • Turn the engine to exactly 1/4" BTDC (or 3/16" BTDC for a late-model CSR with a 9.5:1 piston) on the firing stroke

  • One way to find the right timing position is with a 1/2" socket extension down the plug hole together with a dial gauge. Or you can just mark off a suitable peg in the plug hole.

  • Without turning the engine, make sure the rotor fixing bolt is loose and rotate the rotor until a white timing dot appears exactly under the hole that is clockwise from the pickup coil

  • Tighten the rotor bolt, making sure the crank doesn't move. The timing is now set.

手順 7 Timing check  ¶ 

Fit a new spark plug Switch the ignition on. You should see ~3A on the ammeter for about five seconds, before the igniter shuts off the current to the coil.

手順 7 Timing check  ¶ 

  • Fit a new spark plug

  • Switch the ignition on. You should see ~3A on the ammeter for about five seconds, before the igniter shuts off the current to the coil.

  • If you see 5A or more, your coil resistance is too low. You need to change the coil for a suitable 4 ohm one to avoid damaging the igniter box.

  • Start her up and go for a ride!

  • If it kicks back or pinks, it's too advanced. If it pops & bangs on the overrun and lacks power, it's retarded.

  • All being well, the engine should pull cleanly and run well... If it feels fine, give it a good thrashing ;-)

  • After your ride, pull the spark plug and look carefully at the earth electrode. You're looking for the heat "telltale" mark to be close to the bend. Closer to the plug body = too advanced. Closer to the tip = too retarded. The plug shown in the picture is about right.

  • You now have a spare Wipac points plate and advance/retard mechanism. These are almost impossible to find second-hand. Hopefully you won't need them again!