Topic: Bent / Broken Valve - Cause?

[jakec]

Go down to post #3 for pics 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.

[754]

If you got it unstuck, it will likely stick again.
 If you pull it apart and stem looks ok , you might be able to ream guide..... slim chance i would say.

[jakec]

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.

[jakec]

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.

[754]

Piston was not kissed , it was SMACKED..
 Not sure pistons have to be changed.
Did the springs break ...notice anything there ?

[jakec]

I will look at the springs again, but from memory they were not broken. The top of the valve is still installed in the seat at the top of the spring.

[maxheadflow]

You'll want to check the rod. Make sure it's not bent.

[maxheadflow]

Looking at the end of the valve, it looks smooth. Did the valve end break at the keeper groove or did the keepers fail and what we are seeing is the top of the valve stem?

[jakec]

The keepers are still there and the end of the valve is still installed with the keepers, washer, and spring all connected. What you are seeing is a point in the shaft of the valve. It sheared off but looks pretty smooth.

[maxheadflow]

Yeah, Hard to tell from the pic..

My guess as to the cause would mainly be age.. Something I wonder about whenever I take my cb750 to 8500.  IIRC the 70 cl350 was 9500. 

[bryanj]

 Piston will run, seen a lot worse. If you hone it piston clearance will go too big if you fit new standard just clean bore with emery tap or flap wheel. I woupld fit 2 valves and make sure guides are not damaged.
In UK we had a 250 version of that and only thing that went wrong was if thrashed from cold the piston rings would break. There is a centrifugal oil filter under the circular cover on clutch case that needs cleaning regularly and make sure cover is re fitted correctly

[jakec]

This bike is my girlfriend's. I also have the same bike, 1970 CL350 K2. I believe the first three years 68-70 were all 10.5k redline. I never get it out to 10.5 but I do often get it to 8.5 on the highway. Is "age" really a cause? Seems kind of like a non-answer (no offense). I just want to make sure I'm not slapping this thing back together just to have the same thing happen again.

Bryan, you think I should run the pistons, just clean the bore with emery cloth? And replace both valves on the #2 cylinder? I would have to assume that the guide is damaged because the valve is still stuck in there (haven't tried to bang it out yet).

[754]

Guide is nit expected to survive, even  if it did... unless you carefully knock off any burrs on broken piece, you WILL FINISH IT OFF.... If by a MIRACKE  it did not crack or bend, valve stem has to slip out with light pressure.
 Shoukd be changed anyway..

[bryanj]

Not both on that cylinder but both exhaust or both inlet whichever broke, you only need to emery the bore if fitting new rings,  if refitting what you have leave all alone.
Might be more economical to get a used head BUT strip it and check all the valves/guides before fitting.
If this enginehad beenstood up for a while that could have caused enough corrosion for a valve stem to fail. Shame you have to pull the engine to do any work on these but a least its not as heavy as a 750!!

[Kevin D]

What happens if the valves are set with the index mark in the wrong position (with the index mark towards the cam)? Rocker arm not centered on valve?

[jakec]

Funny you should mention those index marks because on this bike they were correct. But on my 350 which has never given me a problem and runs great, one of the adjustment index marks is facing the wrong way. But I am still able to adjust the valve normally.

I have looked on eBay for used heads but usually they look like they’re in worse condition than mine. And they are not all that cheap. So I will probably just get valves and a guide.

[jakec]

Also I should mention that when we bought the bike the guy said he had just done new rings. So he did get into the top in. Which could be somehow related to the bent valve which happened down the road..

[bryanj]

Perhaps he had the valve tiing out and in turning it over slightly bent that valve before getting it right

[jakec]

Are you saying spinning the adjustment screw around and round could have bent the valve? Doesn't it only press on the end of the valve (By pressing on rocker)?

If I am going to take the head in to get 2 valves installed should I just remove all 3 valves and check them to be sure they are straight?

[bryanj]

No, he may have had the cam chain on wrong so cam timing would be wrong and things hit, its easyto get wrong on these motors.
I said before if it was me i would change both exhaust valve(it was an exhaust that broke?) but yes check the 2 inlets as well, there has to be a reason the valve failed and you need to rule out all you can so it doesnt happen again

[jakec]

Before tear down I compared the index mark on the cam to the stator and it was lined up correctly. What can be installed wrong other than cam timing off, to create this problem?

Also common motor sells a set of 4 new valves for $100. Whereas a single exhaust valve is $50. So I will get all 4 and ask shop to replace.

[754]

 You got real lucky.
 Below is what usually happens ..or worse.l
 A buddy did that to his wifes Honda on the weakend.

[bryanj]

It was lined up correct when you took it apart but you said the po put new rings in so did he get it right first time or wrong and tried turning it over stressing the valve before putting it right-----who knows and would he admit it anyway

[jakec]

I see. Yeah my experience working on the bike so far was that he never di anything the right way, always using zip ties and black sealant, electrical tape, etc all over the place. We bought the bike because it ran extremely smooth and quiet when we went to go check it out. But that didn't last long! haha.

[HondaMan]

I see. Yeah my experience working on the bike so far was that he never di anything the right way, always using zip ties and black sealant, electrical tape, etc all over the place. We bought the bike because it ran extremely smooth and quiet when we went to go check it out. But that didn't last long! haha.

I know JUST how you feel....