I was riding about 25 mph, just shifted into 3rd gear and it went pop. Not much noise, no scrapping noise of warning, just let loose and locked up. I have 34,000 miles on the bike, I was hoping the woodruff key would have sheared off, and left the crank intact, but apparently the woodruff key is stronger than the crank end. The majority of the rotor is in 1000 pieces, with the exception of the steel center of the rotor. The rotor sheared off about 1 inch of the crank stub, just the length of the securing rotor nut. I wiggled that rotor center off the remainder of the crank stub end, but it is slow going, the woodruff key or other debris were binding on the remainder of rotor.
I looked at some U-tube vids and found a description of repair of small Japanese engines by cutting the jagged edge of the stub, then drilling and tapping the center of the stub in order to insert a bolt. This is real possibility, not just wishful thinking!
https://www.bing.com/videos/search?q=cr ... 5D6BBF2CF1
I decided to attempt to center-drill and tap the crank and secure the new Lucas rotor with an 8mm 8.8 bolt. I am pushing the envelope into new territory here, but since the crank spindle is on the way on the slow boat from Mr H, I thought I would give it a try.
The rotor sheared off about 1 inch of the crank stub, just the length of the securing rotor nut. The end of the crank stub was stuck in the rotor nut (I will post photos later). It occurred to me that the conical detent in the end of the crank could be used as a centering jig for a pilot hole into the remainder of the crank stub. Sure enough, I took the rotor nut and the broken end of the crank and center drilled it with a 1/8th inch drill bit on my 1971 JC Penny's drill press. The crank material is very soft and drilling went very well, very straight. With this center hole through the broken crank/rotor nut. I was able to use this assembly as a drill guide inside the remainder of the hexagonal rotor core (see photo). With this assembly, I was able to successfully drill a 1 inch deep pilot hole into the center of the crank stub. I drilled a 6.7mm hole into the crank stub such that I can tap that hole for an 8mm bolt.
Drilled out the crank stub with a 6.7 mm drill, set up the rotor nut on the vise and tapped it with an 8mm 1.25 tap. Once I had the rotor nut tapped, I wrapped it with two winds of masking tape to take up any lash between the rotor nut and the remaining "hex center" of the exploded rotor. I then carefully began to tap the actual rotor stub. I used three different taps, one pointed, one less pointed and one blind hole tap. I cut about three threads depth, then backed off and used a magnetic screw driver & oil to collect the chips of metal. From what I gather on the web, failing to clear the chips regularly while cutting the threads in a blind hole is main cause of tap breakage. I went slow, it took about an hour to tap threads 1 inch into the crank stub. All went well. My two inch 8mm bolt went in nicely. I then slipped a Lucas rotor onto the crank stub, inserted the rotor nut into the hole, then threaded in the 8mm bolt and washer to secure the new rotor/nut assembly. I found the new 8 mm bolt head protruded 2 mm farther into the primary case and was interfering with the primary cover. I then ground off approximately 2 mm from the top of the bolt head and it seems to clear. I filled the primary case with 200 ml oil. and kicked it over several times to listen for any scrapping, hearing none, I switched on the power, fuel and it started on the third kick. I let it idle for ten minutes waiting on another explosion, but all went well, ammeter showed a normal charge. I then took it around the block, everything sounds fine.
I ran the bike for about 15 miles, changed the fluid and then ran it for another 50 miles. I will post a photo showing the shims needed to fit the Lucas rotor (which is about 5 mm thinner than the Indian rotors). You will be able to also see the file marks where I skimmed 2 mm off the head of the new 8 mm bolt.
I will post photos when I find a way to reduce the file sizes which are over 1mb each.
