[billjensen1962]

My 1968 CB350 just quit while riding. There sounded like a slightly different noise coming from the top end before it died. I took the points cover off to check the timing and pushed the starter (see video) and the points don't move. This looks serious???
Anybody have any ideas where I would even start to get this fixed?
Thankyou!

 

[FrankyV]

It looks like the points cam is not spinning at all, make sure it is installed correctly and the bolt is tight. If it is then you have to determine why the cam is not turning, it may be a broken cam chain.

 

[Simo]

It looks like you need to rebuild the top end

 

[J-T]

Remove one of the valve adjustment plugs. That way you'll be able to determine if the camshaft is turning. When you know that you will be able to decide where to look next.

 

[ancientdad]

The engine sounds like what I've always called "asthmatic", as in not breathing properly. Sounds like weak compression when turning over so I'd guess the cam chain broke or the bolts came out of the cam sprocket. You'll definitely know for sure about cam movement when you do what J-T suggested

 

[billjensen1962]

I removed the valve adjustment plug and turned over the motor, nothing moving. So Im thinking as AD stated the bolts came loose or the chain broke. Anyone know of where I could find out how to do that? Common Motor has a video on cam chain guide and tensioner replacement which appears to be close to what I need. As far as getting to it from the top. However it doesn't show how to get the old one out or the new one in?
Thanks

 

[ancientdad]

Since you can't tear down the top end of the engine in the frame, the first step will be to drain the oil and pull the engine out. Get it on a bench and pull the top cover off and things will be a lot more evident and clear as to what you need to do. Probably going to have at least one bent valve, possibly more.

 

[billjensen1962]

My skills are probably better than the average guy on the street with a wrench but not sure about this? Is this something you think a normal person could handle? I've pulled some V8's in my day and rebuilt one from the block up but not so much with motorcycles so far...

 

[Simo]

Id do it, and im pretty normal.

 

[ancientdad]

Id do it, and im pretty normal.

Yeah, you look normal from here... :lol:

but seriously BillJensen, if you've rebuilt a V8 you can do this. Yes, it's *scary* OHC, but it's still a 4 stroke engine and there's more help here than you'll get anywhere - and plenty of those that own the same bike you do.

 

[billjensen1962]

Thanks, it's too nice of a bike not to try and not worth much the way it is. It will be my winter project!

 

[billjensen1962]

So more news on my CB350. I'm starting to get to the point where I'm finding out a bit more and could use some help. I'm preparing the bike to pull the motor but,

I lifted up the valve cover and turned the motor over by hand. The cam chain is intact and turning see video. The valves and cam however are not see video. So, I'm thinking the bolts came out that hold the sprocket onto the cam?
Is it still necessary to pull the motor? Can this be fixed from the top somehow?

 

[Yendor]

There is not enough clearance to remover the upper cover from the cylinders to access the cam chain sprocket.

The motor needs to come out.
Also you will need to find any broken missing parts (I.E.: cam sprocket bolts).

 

[fxray]

I agree with Yendor, and will add that you have likely already bent some valves when the cam sprocket bolts let go. If it didn't happen then, it would have when you turned the crankshaft while the cam was not turning. Sorry.