Drive Sprocket Shaft Dilemma

[Netter]

A little background to start, I was out riding the other day and heard a terrible crunching grinding noise. I pull over get the bike into neutral let go of the clutch and black oil with confetti starts leaking out of the engine....
this is what it looked like when i took it apart




so I went out and found a new engine,
the engine looked good except for the drive sprocket, it had an awful lot of play, after removing the cover i found that there was a round spacer poorly welded to the drive shaft acting like a stop for the sprocket (it looked like it took some beating from the chain).
after finally getting the spacer off i found that there was no threads on the shaft...



that is my problem, any input on how to fix that problem besides replacing the shaft?
I was thinking about trying to use a die to re thread the shaft, but then the lock nut would have to have a smaller diameter as i can slide the nut on the shaft as it is...



any input would be greatly appreciated

-Thanks
Annette

[tampaFZR600]

OMG THOSE VALVES....or lack there of.

Good luck man.

[DonTZ125]

Scavenge the two engines, two to make one...

[sweekster]

[yamaha_george]

Scavenge the two engines, two to make one...

That is the simplest way of curing the problem.

Trying to put fresh threads on that shaft is not too likely the shaft is hardend (or it was before the Numb nut PO put a weld on it.) Chances of getting the threads straight are small where it is , removing it would make life simples . BUT then you might as well put your old engines shaft in.

Else take the shaft to a machine shop with a new sprocket nut and have then add metal to the shaft , machine on a new thread to suit the sprocket nut ( none of that would be cheap )

[Netter]

Would drilling a hole through the nut and the shaft and adding a codder pin work to hold everything together?

[cad600]

Would drilling a hole through the nut and the shaft and adding a codder pin work to hold everything together?

There is a lot of force on that area. I wouldn't put a pin in it to use as a primary retaining method.

[yamaha_george]

Would drilling a hole through the nut and the shaft and adding a codder pin work to hold everything together?

The Problem with a Cotter pin is the side pressure for keeping the sprocket from rattling around on it splines PLUS keeping the pin away from the chain is simply not viable. As i stated elsewhere that shaft is hardened and would require a pin of similar hardness which would again cause a problem

PS
I am assuming you are NOT referring to split pin but a cotter pin which is a wedged dowel as per bicycle pedal cranks ? I ofter hear split pins being wrongly named as cotter pins .

[Netter]

I guess I was thiking of a split pin but, i was really just trying to get that idea across or drilling a hole straight through and using a pin of some kind to keep the nut in place.
It looks like I will be takeing the drive shaft out of the old engine and putting it in the new one, is there any way to that with out taking the lower crankcase apart?

[cad600]

I guess I was thiking of a split pin but, i was really just trying to get that idea across or drilling a hole straight through and using a pin of some kind to keep the nut in place.
It looks like I will be takeing the drive shaft out of the old engine and putting it in the new one, is there any way to that with out taking the lower crankcase apart?

Nope.