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Discussion Starter · #1 · (Edited)
Go down to post #9 for photos of valve, piston etc.

We have this 1970 CL350K2 which has about 4,500 miles on it. We recently got it running after rebuilding carbs and messing around with points and coils, etc for a bit. After all that the bike was running great. I took it for a few rides around the city before handing it over to my gf. She did some city rides as well. At this point we had put probably 60 miles on it. The only thing I had noticed at this point was the valves were a little loud, but I planned to do an adjustment soon after some more miles. Also there was a bit of oil leaking from the oval shaped gasket behind the tach drive area.

This weekend she rode the bike about 40 miles on freeway (60-70mph) to my parents house. Everything seemed fine. Then the next day it was time to go back. As we pulled into the city at the end of the trip she said she lost power. The fuel level had got down to reserve, and she flipped it on but it didn't help. She rode the bike home the last mile with it running on one cylinder.

So last night I got into the bike looking for the solution. Eventually I see that the exhaust valve on #2 is stuck wide open. If I kick it over I can see the intake valve move and the exhaust just stays right there. I don't think the valve hit the piston because the bike still kicks over smoothly and will run on the left cylinder. As for the cause I am not sure what it could be. I want to rule out fuel starvation > lean condition because the EXACT thing has happened to me on my CL350 (run out of gas at highway speeds and hit the reserve a little late. Now I have to pull over and pump on the fuel lines to get it going again) SO many times. And my bike is still fine. Maybe oil starvation.. but only for one valve? Or do the exhaust valves just get hotter and therefore it went first?

Anyways I'm trying to figure out what I can do now to see if it's just stuck or if it's bent... if it isn't bent I want to know if it's possible to free it up and be done with it.
 

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I had the exhaust valve do that on a Honda S90 one time, shortly after I got it running. I tapped the end of the stem with a screwdriver and hammer and it popped right back into position. It did it again the next time I rode it, and I “fixed“ it the same way. It never did it again after that.
 

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Discussion Starter · #3 ·
Wow.. are you talking about tapping on the end of the tappet adjustment? Since you can't really tap on the valve itself of course.
 

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In the case of a 350, you’d have to tap on the rocker arm right over where it contacts the end of the valve stem.
 

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Discussion Starter · #5 ·
Since the valve is totally open now that means the spring is depressed. So actually I guess I could move the crank so that the rocker arm is loose then I would have a lot of space to stick something in and touch the top of the valve. Like perhaps I could use a flathead and lever it against the rocker arm a bit to apply some relief to the spring and see if it snaps back into place.
 

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Sounds like a plan. Depressing it just a bit more and releasing it may unhang it.
 

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Discussion Starter · #7 ·
Ok, I am going to try this, and also look at the advancer pin on the camshaft to see if the PO maybe got the timing off..
 

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Discussion Starter · #8 ·
I went to inspect the cam indexing mark. When the rotor's LT mark is lined up on the #1 compression stroke the index mark points down at 6:00. When LT on #1 exhaust stroke, the mark points up at 12:00. So I think that the timing is fine. I noticed the start of some yellowing on both headers (about 1-2" at port). Even on both sides. Carbs had just been rebuilt. I never did a valve adjustment on this bike. So far I'm not sure of the cause of the bent valve.

However I could see that the top of the valve moves up and down with the tappet when the crank is turned. But the bottom of the valve never moves (see through spark plug hole). So the valve is broken. I have pulled the engine now.
 

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Discussion Starter · #9 ·
Ok so teardown notes:

1. Valve obviously broken and looks "different" on side facing combustion chamber.







2. Piston has been kissed. Ignore all the oil on the piston crown, that just happened during disassembly.





My impression is that aside from the broken valve, everything looks good. The color of the pistons and valves looks normal to me. I am no sure what causes the different texture on the valve that broke. I also found oil EVERYwhere during disassembly. I did not see any particularly dry spots that would lead me to believe that oil starvation was the problem. I have not inspected the oil pump yet but I should do that and possibly rebuild.

What I would like to do now is figure out what would cause this so it can be avoided. And then put the engine back together ASAP. I would like to do the minimum needed. What I'm thinking now is:

Buy:

Gasket set & O rings

Piston Set

1 Valve & guide

Do:

Lap & install 1 valve

Hone & install new pistons

Clean surfaces & reassemble engine with new gaskets & O rings.
 
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