Hello Graeme
Here are machining details for the drive gear sleeve mod
The Mk 3 starter system can be made to reliably perform like a modern bike, so much so that i,m seriously considering removing the kickstart altogether and the bonus of that being i can then make some rearsets that don't have to accomodate the kickstart so can be neater in apperance
This mod increases the angle of the sprags so it has no chance of 'flipping' and consequently wrecking the sprag/drive gear/sprocket
Obtain 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 bore
turn/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 radius
Press 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 Done
Ken 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)
My last commando (thirty years ago) crunched its sprag in Stockholm (Sweden) when I was going to the Britti Ralli in Finland. Thank goodness for kickstarts! That bike had a two pole starter. This was years before I got myself a well equipped machine/workshop.
I have since done this modification for a number of people and i now use the inner race from second hand bearings removed from overhauled industrial gearboxes. Although this requires removing more metal to get the sleeve to the right diameter.
I have also converted brand new harley davidson starters to fit the mk3 commando. I have one of these on my MK3 and since i got her back on the road in april last year i have not used the kickstart at all, and up until january of this year she lived outside even down to subzero temperature, and she still started on the button.
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!)
I run a duplex chain on my Mk3 primary drive as according to Andy (the chainman) No one makes decent triplex chain anymore.
Regards
Pete
dobba99
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Joined: Sun Jan 26, 2014 1:34 am
Location: Yorkshire, England