Topic: Exhaust Valve Snapping Shut

[Scirocco88]

1969 Honda cb350 twin

It was recently (about a month ago) running very well. It had a terrible oil leak so I tore the top end of the engine down. Back together and back on the bike I tried to start the bike. It would kick over where as before it was a one/two kick starter. Also when trying to turn the bike over it there is a horrible banging/knocking sound from the left cylinder on the top end.

I thought the timing was way off and a valve was hitting the piston. Thankfully that doesn't seem to be the situation here. I turned the engine over by hand with a ratchet on the generator and the valves are all opening and close when and how they should except for one: the left side exhaust valve. That valve is opening fine and on time but at the end of the exhaust stroke the valve seems to hang (meaning stay open) and then all the sudden snap shut making a loud banging noise. Where is should be slowly closing as I slowly turn the engine over. I tried loosening the valve via the valve adjust screw but it never gets loose.

During the tare down I left the valves alone. They stayed in the springs. So I'm a little lost as to what could have changed from before the oil leak fix to now that would effect the exhaust valve. Any thought would be greatly appreciated.



-Thomas-

[scunny]

did you loosen the rocker shaft ? if this is not tight the rocker can hang up then snap closed

[bradweingartner]

When you took the rocker cover off did you loosen all the tappet adjusters before and adjust again afterwards? You might have bent them and it's hanging up on the end of the stem...

[olds-cool]

When you took the rocker cover off did you loosen all the tappet adjusters before and adjust again afterwards? You might have bent them and it's hanging up on the end of the stem...

I was going to suggest the same thing since it happened to me.  That's the same thing that my 500 was doing after I put the valve cover back on.  Either I missed the instruction saying to back off the adjusters or the manuals don't say it.  Luckily I had an extra head full of valves to replace the 6 out of 8 that I bent.

[bradweingartner]

When you took the rocker cover off did you loosen all the tappet adjusters before and adjust again afterwards? You might have bent them and it's hanging up on the end of the stem...

I was going to suggest the same thing since it happened to me.  That's the same thing that my 500 was doing after I put the valve cover back on.  Either I missed the instruction saying to back off the adjusters or the manuals don't say it.  Luckily I had an extra head full of valves to replace the 6 out of 8 that I bent.

Somebody is going to be kicking their own ass when they figure this out... 

[Scirocco88]

Just so I'm clear: are you're saying I'm supposed to loosen the rocker arm pins or am I supposed to turn the engine to the spot where all four rockers are lax? And when you say rocker arm cover you're talking about the oval shaped side covers on either side of the cylinder head cover, right? I don't think I did that when reconstructed my engine this time or any time. I don't think it's mentioned anywhere in the book.     I guess I just got lucky the other times.

It seems like I just got the engine back in the bike and got it all hooked up, too. Now I have to take it off again. I hate that you can't do any sort of internal engine work with the engine still in the frame on these twins.

Plus I was really trying to avoid any valve work since I don't have the proper equipment to take the valves apart. 

[bradweingartner]

To be honest, I didn't even notice you had a twin. But I'm going to go ahead on the assumption that it's similar.

Before you take the rocker cover off, you need to pull the little covers where the valve adjustments are and loosen all the nuts and screws out to take tension off the valves. Otherwise when you put it back together things can bind and get in the way and that's bad news and sounds like your problem... So a valve got tweaked and now it doesn't slide smoothly through the valve guide.