Honda Twins banner

1 - 8 of 8 Posts

·
Registered
Joined
·
55 Posts
Discussion Starter #1
I brought my head to the local machine shop and my guy told me the exhaust valves were bent and I would need to replace them. Otherwise everything was ok with my top end.

Would there be something that would cause this I need to look into further? I know that my cam chain guide was worn, but the chain and everything else looked ok.

thanks
 

·
Registered
Joined
·
785 Posts
I just can't see it happening, bending two exhaust valves is too far out without a broken cam chain. And even still I think it would be an intake and an exhaust valve, not two exhaust valves.
But, I am not a twin expert, I see DOHC Honda 4 cylinder engines behind my eye lids.
 

·
Registered
Joined
·
55 Posts
Discussion Starter #3
I have to get more info, that's what he left me in a VM. I took off the cylinder and found the chain roller was pretty beat, I've attached a photo. Do the cam chains have a master link? I can't find one.
 

Attachments

·
Premium Member
Joined
·
667 Posts
I have seen engines that are run on rotten gas have exhaust valves stick and then get bent. This was on a small engine but I guess it could happen on these twins as well.
 

·
Registered
Joined
·
70 Posts
Just a thought but could this be caused by a simple case of running the bike too hard? Running past redline, high revs all the time causing valve lash, and the valve train not being able to keep in synch w/ the pistons, then the pistons would contact the valves?

The clearances from piston to vavles are pretty close and don't think it would take much to cause some point of contact.

again, just a thought
 

·
Registered
Joined
·
6,495 Posts
smbevma said:
I have to get more info, that's what he left me in a VM. I took off the cylinder and found the chain roller was pretty beat, I've attached a photo. Do the cam chains have a master link? I can't find one.
No, no master link.

If whatever went wrong happened when the bike was running (maybe the cam chain started flopping around), there's enough inertia to keep the pistons turning long enough to make sure ALL the valves get bent. Check by putting the head on its side and pouring acetone into the intake/exhaust ports. Check for leakage around the valves. Intakes are actually more likely to get bent, they're larger......

Your rollers all look shot. Their remains are probably in the oil pump and all over the engine.
 

·
Registered
Joined
·
785 Posts
tbpmusic said:
Your rollers all look shot. Their remains are probably in the oil pump and all over the engine.
Looking something like this but, not as bad?
 

·
Registered
Joined
·
55 Posts
Discussion Starter #8
According to the machine shop mechanic (who has had 3 cb350's among his other bikes) my problem stems from the shot cam chain tensioner, roller wheel and guide changing the timing and causing everything to smash into each other. The exhaust valves were leaking, which was causing my low compression issue. I ordered all new valves, rings, and chain tensioner-related parts. I also honed the cylinders. After I paint the engine and put it back together I hope to have a good running bike.
 
1 - 8 of 8 Posts
Top