Norton 850 MK3 starter motor systemMaking it reliable and long lasting.Converting a new World Power Systems Harley Davidson pattern starter to fit the Commando Mk3This all came about when in early 2014 I bought a 850 Mk 3 Commando minus its starter motor, the starter was in bits in the spares i got with the bike.Wanting to refit the starter i did a bit of research on this and other websites i decided to purchase a WPS 5780 BN starter from Eurocar parts (this starter is for certain models of harley davidsons) primarily for the fourpole frame and brush plate that can be retrofitted to the original prestolite Norton starter. (this mod is well documented elsewhere) For all of 2014 this arrangement worked well although the bike sometimes had to be kickstarted in the mornings.Over the winter i had the engine in bits overhauling the cylinder head and during that time i decided to do something with the redundant rotor and end caps from the WPS starter as they are superior to the original prestolite items.The following words are what i came up with.The original two pole Norton Prestolite has oilite bush bearings and although they do the job, they do not control end thrust. This is controlled by the drive end cap, this has an extension that carries the oilite bush and it is this extension that has to resist the thrust of the rotor when the motor is energised. All electric motors have what is called a magnetic centre, that is when they are energised and revolve the rotor wants to revolve on its mag centre. With the norton prestolite, the rotor is thrusting towards the drive end cap, This wears away the bearing extension, saps motor power and wears into the rotor itself until the rotor windings contact the drive end cap, causing poor motor performance.The Prestolite motor fitted to the Harley has a large ball bearing at the drive end and this easily copes with the rotor end thrust.The WPS non drive end cap has a needle roller bearing as well This ball bearing is too large to fit in the end cap for the Norton as it would interfer with the idler gear spindle hole, a smaller bearing is required. I cut off the harley drive gear from the WPS rotor and cylindrically ground the bearing register down to fit a 6203 2RS bearing. Without removing the rotor from the lathe I drilled the shaft to accept a new gear that i machined up and heat treated. This is loctited into the rotor with high strength retaining compound (this stuff is the dogs dangley bits when it comes to holding stuff together)A new drive end cap is then machined up to accept this new bearing arrangment.Swap the brushes around to reverse the motor rotation.Motor rebuilt and sealed with silicone, refitted and started the engine first press after its rebuild and has started the engine all year from clap cold. I have only used the kickstart to turn the engine over when adjusting the valve clearances. I am seriously considering removing the kickstart altogether.Fitting the Nortonised WPS harley starter left me with a complete original norton prestolite in need of some TLC. I ground the rotor shaft drive end to fit the 6203 bearing like the WPS rotor. Obviously you don't have to make a new drive gear as its already there.I drew up and cut out a fill in piece to fill the cavity in the prestolite drive end cap, this was bonded into the original cap, allowing it to be machined out to accept the 6203 bearing.At the non drive end (where the brushes are) the shaft itself was ground to fit inside a 9mm needle roller bearing and the end cap bored out to fit this bearing.This motor had suffered from rotor thrusting and had worn the rotor windings into the drive end cap. I dealt with this by painting the rotor windings with proper insulating paint.About this time I was given another original two pole motor that had had a four brush conversion fitted at some stage in its life. This was in even more of a sorry state than my original. I had bought from ebay a set of Accel field coils for a harley prestolite along with new brushes and brush plate. So i set about that motor as well. Fitting the rolling element bearings and now removing the field coils from both original norton frames. After field coil removal i blasted the frames to remove the buildup of rust inside that these motor accumulate. I fitted the Accel field coils to one frame and the field coils i removed from that one i paired up with the other frame to make two four pole frames. The original norton field coils were reinsulated with fibre glass tape and connected to four pole configuration. Anyone who has done this will tell you it is not an easy job, as the input connection cutout in the norton frame is directly in line with one of the core irons, this dosen't matter with the two pole frame as that core iron hasn't got a field coil on it, when you fit the other field coils space is very cramped. Add in the field coils are solid copper and it is a real headache to get it all in and not short something out.The harley frame is better in the repect that the input connection cutout is between core irons so giving you a bit more space (but not much more!) The original field coils are connected to the frame by spot welding, I soldered the connection onto the frame using plumbers solder, unless you are confidant you can solder this connection do not attempt this work as it is critical that this connection is good.Having painted the frames inside with the insulating paint and outside with engine black lacquer they were reassembled and test run.These can be used on 'original' machines but without the 'original non starting' That sorts the starter motor out, now for the spragThis is slightly different to the Ken Merrick mod outlined on this website ages ago This mod increases the angle of the sprags so it has no chance of 'flipping' and consequently wrecking the sprag/drive gear/sprocketObtain a LRT354220 hardened bearing inner race from your local bearing stockist (should cost only a few pounds, I got two for less than a tenner)Turn/grind the drive gear spigot (what engages with the sprag) down to 1.450" diameter. make sure you have a good radius tween the spigot and gear i.e. NO UNDER CUT You can do this with the needle roller still in place, just plug the boreturn/grind the bore of the your new inner race so it has an interference fit of 0.002" (1.448") chamfer the bore so it will sit over the radiusPress the two together ,remount in the lathe and turn to length. Turn/grind the OD down to 1.632" (this is an increase of 0.007" over standard)radius the end so it is an easy fit in the sprag.Job DoneKen Merrick did his mod a little differently, he glued the sleeve to the drive gear with loctite retainer. He also internally ground out the engine sprocket to remove the sprag dig in marks (approx 0.010") and increased the size of the sleeve accordingly. I have found that it is not necessary to do this.Even if you have to pay someone to do the machining for you it should work out cheaper than replacing crunched bits for new ones. The drive gear and bearing sleeve can be turned with sharp carbide tools but I used a toolpost grinder to finish the diameters (Same toolpost grinder i used to reface the cam followers when it replaced my camshaft) My last commando (thirty years ago) crunched its sprag in Stockholm (Sweden) when I was going to the Britti Ralli in Finland. This was years before I got myself a well equipped machine/workshop.Belt drives run dry and this starter system do not mix well. The sprag requires lubrication or it will prematurely fail, If it fails and seizes the sprocket to the drive gear you will kiss your motor goodbye as the starter motor will not be able to withstand the huge increase in revs (60,000 plus) If you do have to run a belt drive make sure it can run in an oil bath (with oil!)RegardsPeter Shand
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