Dog mechanism and forks:
The cush is in the 4-spring clutch centre (as per the alternator bikes).
The dog inner is splined on the crank with lobes onto the normal crank sprocket. Its retained by the crank end nut, which is turned down a bit to the same dia as the OD of the splined section of the inner dog. on this sits a sleve. on that sits a 4516 needle roller that is pressed in to the inside of the outer dog assemly. so the outer dog assembly can move in and out along the crank axis - 9mm movement including 6mm of engagement. There’s 28T 06B sprocket on the outer of the outer dog.
The fork engages a slot in the outside of the outer dog and sits on linear bearings, which slide on hardened rods against springs into a base piece. The base assembly is attached to 2 of the 3 bolts that hold the primary case to the crankcase, around the crank. If I’d have got the location of this piece better I would not have had to move the oil filler plug in the case – but…
There’s 2 ip rated microswitches under the fork. (the pics show when it was just one - I hope the switches survive that environment.) One has a spring mechanism to allow a long overtravel so it engages just prior to the dogs making contact. The other when the dogs are fully home. The switches activate parallel 120A relays to the starter. One relay has a resistor block in series (3x 0.8ohm 50W in parrallel = 0.27 ohm, mounted on aluminium, for low power initial dog engagement). this resistor aproach was easier/cheaper than pwm or 2x 6v batteries and the heat is minimal.
Starter etc:
The starter motor is a mitsuba sm2(?) off an xj750 or similar. Its about 700w with internal planetary gears. I had to modify the brush plate and wiring to make it run backwards. Mounting it rigid was not easy. It has 2 mounts at the far end but originally is held by its collar at the drive end. It has 2x 6mm threads for a cover plate - not strong. So I made shaped spacer held off by 2 adjustable bolts for chain tensioning. that sits on a 20mm square bar perpendicular to the engine plates/starter mount bracket. it has not been easy to stop the starter motor from twisting a little (when under load) as the sprocket/drive end is so far from the engine pates (on which it all ultimately bolts to).
The mitsuba starter has a weird 31T 13mm spline – I couldn’t find a matching splined sprocket so machined down its original gear to make a collar inside the 06B 15T sprocket. I had sheer pins between the sprocket/collar but they broke repeatedly, spun to cause wear, slop, misalignment and so are now held with thick pins and bearing retainer. Not great. I'll need to rework this one day.
also the location of the starter needed to be as close to frame bolts as possible, on an incline to allow oil to drain back down, high enought to prevent the mudguard hitting it under fork dive and low as posisble to minimize chain length.
The chaincase:
it wasn't that hard to modify and quite fun hammering and shaping metals bits. moving the filler was annoying and making it oil tight a challenge. fitting/removing the case now requires the starter chain removal. not good design.
I feel compelled to say - its a project - could do better. to get this far it took 2 different motor types, 3 chains, 4 fork designs and a unknown number of electrical versions. if you have any specific questions ask away. And John I'll be very interested to hear what you come up with for the ZB.
