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OR . . . You could have the threaded portion cut off the main shaft, drill and tap the shaft, and fabricate a threaded piece to replace the damaged portion.Triumph twins retained the alternator rotor with a threaded stud and nut for decades.
Now thatís an idea I hadnít thought of, interesting. The shaft and flywheel are one piece.
I might be able to help , what is the diameter of the flywheel ? Peter ( in Burnaby, B.C)
Drill the end and thread the hole. Works for Moto Guzzi and BMW.Loctite (RC680) in a quality stud and you have an easy lifetime repair.If it ever gets messed up just torch out the stud and install a new one.
I'd try what Huzo is suggesting. The tapered shaft part and the woodroof key slot is clean so once the nut is tightened enough, it should all lock in nicely (obviously, they couldn't get it back out). If the tapered shaft were scuffed from stripped woodroof keys over the years, then you'd have to rely on a lot more torque on the nut to lock it all down.
I think this is the safer route for me, I trust my ability to weld up the shaft tip but my thread turning skills on a lathe are crap. I can drill a straight hole with the lathe, just have to be very careful to not snap a tap cutting threads. I need to decide upon a stud diameter, I think the threads are M12 on the tip, could probably get away with an M8 or M10 stud.
If in doubt, load the tap into the tailstock, and just turn the chuck by hand or with a strap wrench.Just for giggles, check Mcmaster.com for shoulder bolts. You might get lucky and based on the thread size you pick, end of with a should diameter that matches the flywheel inside diameter.
If that is a flywheel on the crank I'm pretty sure the key is used for timing purposes, not flywheel retention. Flywheels are often located with keys but retained by being bolted firmly on a locking taper. They are fit dry on the taper so they lock. The BMW R60/2 locks its flywheel on to the tapered crank with a single bolt through the center of the flywheel. This bolt is tightened to 175 ft/lb. It is also keyed to put the timing marks in the correct place. If the flywheel is not tightened fully it shears the key then damages the taper.If your crank is similarly configured. I would suggest you make the stud out of a 12.9 bolt using the threaded portion as a stud (cutting off the rest) Drill and tap the crank the diameter and pitch of the existing stub. Make the working threaded hole depth 2 times the diameter of the existing stud. That way it won't strip out. Then torque to original specs, if available. Otherwise use a good reference chart for the materials used.
Not a lot of meat at the smallest of the taper but it is supported by the 12 mm stud inside and compression from the flywheel outside. Alloy steel stud only. Either cut it out of a 12.9 bolt or socket head cap screw if you can't find the equivalent stud material. Stainless is much weaker. There's a reason they put a 12 mm thread there.
I see where you going with the shoulder bolt, do you know if anyone makes a stud that is 12mm on one side and 10mm on the other?Based on the measurements I took off a good 200 cc crank, the threaded end of the crank shaft that takes the rotor nut only projects 13mm (1/2") and is 12mm diameter. I am a little reluctant to use a 12 mm stud into the end of the crank, not much meat there at the end of the taper. I think a 10mm could be drilled and threaded into the crank shaft. Alternately I could just machine up a 10 mm deep nut for the rotor securing fastener. Pretty sure the thread pitch is 1.25 fine (maybe 1.5 - will check tomorrow), will probably need to order a stud, should I use a carbon steel stud or a stainless steel stud?This is the deep nut used on the rotor, off another engine I haveI usually tap threads on parts I can chuck in the lathe and use a spring die holder tool in the tail stock to keep the tap straight and under light pressure, turning the chuck by hand while holding the tap wrench stationary, rocking the chuck back and forth to clear chips. I can chuck up the crank flywheel in my 4 jaw, center it and if I am real picky set up a steady near the tip before drilling and tapping.
I am missing something here. I thought I saw pictures of your lathe in a previous post and it looked nice. You all know lathes are great at making round parts and round parts with threads right?. Why are we not thinking of making parts exactly as we want instead of buying one that is pretty close. I think a little more time to learn how to use a lathe is in order. I have been making parts for quite a while and these are some of the most basic parts one might make with a lathe. I have seen your work on more than a few bikes and see no reason lathe work should not be an easy step forward.
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