OK, I give up.  

Dave, how did you get this picture???

"The flange broke off the back of the sprocket that goes on the crankshaft and holds the primary gear.
https://imgur.com/SXPtib"

Very interesting indeed.  So do we have a situation where the cam drive sprocket failed in a way that the flange broke off but the sprocket portion remained engaged....or.....did the entire sprocket fail?  Does Blake have a bunch of bent valves?

If the cam drive sprocket is the root cause (which seems plausible), how did the balancer drive gear pin end up falling out?  

I think it may have been a failure that was a long time in the making.  For instance, the flange fails on the cam drive sprocket, which relaxes the pinch on the balancer drive sprocket, which allows the balancer drive sprocket to start moving, which starts working on the pin, and the pin eventually gets worked loose from the constant pounding back & forth.  That round pin falling out plays a major role here.

How in the world did you get that picture of the fractured cam drive sprocket?????

@DragBikeMike

Valves are fine and made no contact with the piston. I turned the engine before disassembly and it felt like it made good compression. Everything in the top end looked great as far as I could see.

@stewmills

We are just going to part it out. She really needs a more modern bike with fuel injection since it's a daily. It lasted her a good 5 years. Thanks though!

DragBikeMike:  The photo of the broken flange came from a previous post.  The sprocket is splined all the way through, so when the flange broke off the  cam would still be in time.....the loss of the flange does not allow the sprocket to spin on the crank and change the timing.

I do agree that you are likely correct in thinking the crankshaft gear and pin for the counterbalancer likely started moving around once it lost the clamping force when the sprocket flange broke.  It very well could be the pin broke and the counterbalancer shaft went out of timing and that is what happened when the engine blew the counterbalancer out the front of the engine.

BlakeEM:  The crankshaft is a snug fit in the ball bearing - so you won't be able to pull on the end of the crank and get it to move in the bearing and feel any side to side play in the crank.  The movement of the crank to the right side may have taken a while to occur......and that is likely why the failure didn't occur immediately.

Whoah!  

Dave, is that busted sprocket picture from a previous post by Blake....or.....some other member's busted sprocket?

Blake, is that picture of the busted sprocket from your engine....or.....is all this stuff about the busted sprocket purely speculation?  Is your cam chain drive sprocket all in one piece or is it all busted up?

I appreciate your help on this as I have to make a decision based on your answers.  Please clarify.

Also, note that Blake submitted a picture of his right hand main bearing. It looks like it drifted to the left about 1/8" or so.  If that bearing controls the axial position of the crankshaft, what restrains the bearing outer race?  How do you control the axial position of the crank (right/left) if the main bearing isn't somehow locked in place?

Yes.  That's what I'm curious about.  Somehow, that picture didn't show up in the string of posts that I could see.  So, that totally failed cam drive sprocket is all yours.

Thanks very much.  I have no clue why that particular post wasn't in the string that I was looking at, but it clears up a whole bunch of stuff.

What a mess.  Really a spectacular failure.  Your wife is so fortunate.  Good luck with the fuel injected replacement and muchos mahalos for sharing all the great photos.

Best regards, Mike

Dave wrote on 06/29/20 at 19:01:09:


I noticed that as well...

That looks to me where the problem started.