urgent: need advice if I should tear my engine apart

Hey guys, some major engine problems here. I've been having a speed bottleneck problem recently, I just put non resistant spark plug caps on and was testing my bike out. I stopped after going 65 miles per hour, and was idling at a light when my engine just died. Road-side examination found there was no spark, and the engine kicked over very easily. When I got home I found I had power to the coils, so I opened my points cover and found that my camshaft is not moving when I turn over the stator. The cylinders still move, but the camshaft does not. I tried readjusting the cam chain but It did nothing. It's important to not that I didn't hear any kind of crack or break when the engine died on the road, and moving the stator produces no grinding or strange noises. It feels like my cam chain just disappeared. I am supposed to drive down to the barber motorcycle festival tomorrow, I think I need to tear down my engine tonight so I can order parts for when I get back. When I get back I only have a week before I'm supposed to go back to college(stayed home for an extra month to help family through a hard time), and I'd much rather fix it at home. Do I need any specialized tools to take apart the top end of my engine? Am I totally off here? It's also important to note I was getting 115 PSI on a cold start so I will do new rings and cylinders at the same time. Here's a video of me turning over the engine https://photos.app.goo.gl/GCtpMhK4QLYsCWqC9

edit:cb350, 68 fat cam engine on a 73 body

Agree with your diagnosis that the cam chain has snapped (or joining link displaced giving the same result.)

No real specialised tools needed unless you're also removing centrifugal oil filter. Should be a full engine removal job though. Whilst the cam chain can be accessed by removing the top cover, threading through a new chain would be difficult. More importantly though, you might find link remnants floating about the crankcase which should obviously be removed. Could be a big call to get it done within the week if you're not overly familiar with the process. All the best.

Sorry to hear of it. Certainly seems as though the cam chain let go. Typically the 350 uses an endless chain so a link coming apart would only be the case if someone had previously replaced the chain with one using a pressed-on side plate master or staked master. No part of the top end is removable in the frame so yes, the engine will have to come out. If you had not tried to start it (but that's always a typical roadside reaction) you might have gotten away without bent valves, but since it has been turned over a bunch with the cam (seemingly) sitting still there will likely be at least one bent valve. The good news is it won't be horribly bent if so, since the rpms were very low when it shut off so it's likely you avoided valve guide damage. You might try to carefully turn the 10mm-headed bolt in the end of the camshaft to see if it turns, there's always the possibility that the bolt came loose, the advancer slipped out and off the locating pin and the cam is turning behind it. Probably not likely though based on the video.

Hondaholic said:

No real specialised tools needed unless you're also removing centrifugal oil filter. Should be a full engine removal job though.

Click to expand...

If I recall, the clutch has to be removed to pull the shift linkage lever, which requires removal of the filter.

He’ll need to do this to get inside the cases to remove the metal that’s surely accumulated.


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I think previous cam chain breaks end up jamming the crank, so my guess would be cam chain sprocket bolts failed?

One thing you can do is remove your cam chain tensioner and see if you can see the chain, or push the roller to see if there is chain or just empty space.