Weird exhaust valve problem?

JesseeS

JesseeS

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So while reassembling my bike I decided to double check the valves. All was well except one exhaust valve was stuck shut. Took all other valves out, which was simple, but this exhaust valve required brut force and a hammer. Its out now and the valves and head have been cleaned up. They all go in their normal spits but this one valve won't go in either guide, but the non stuck one goes in both. Anybody know whats going on? It seems almost like it expanded ever so slightly. Seems weird the stuck one won't go in either but the regular fits in both.
 
Mushroomed heads on valves are not too uncommon, usually caught at overhaul when measuring parts for wear and such. Unfortunately, the guide(s) that have had that valve shoved into may now be scratched and oversized.
 
I only forced that valve out, did not force it back in. Noticed that it was not going in as easy as the others even at different angles so I just stopped. It was basically like taking a 8mm bolt to a 6mm hole, you press against say "nope" then remove it. I will be replacing them regardless then. Rather do this job once than twice. Thanks for the help guys!
 
With the head mushroomed the damage got done when you pounded it out.
You should have tapped it in/out just a bit at a time till it moved with just finger pressure. At this point you try pushing it out, you will notice it stops when the end of the valve stem hits the valve guide.
At this point you push the valve back in. Use a file and carefully file the mushroomed edge off. Then try to slide the valve out. repeat as needed to get the valve out. You should never pound a valve out, remove the mushroom.
Leo
 
Leo, before I banged it out the valve was closed completely. I started tapping so it opened a bit, then proceeded to push with no luck, then tried pulling, also didn't budge. That was when I pounded it out. It wasn't when the tip got to the end that it resisted, it was almost as if the valve stem itself had gotten larger. Hopefully i'm describing this correctly, but the whole stem seemed to large for the valve to begin with, maybe why it met with such resistance and will not fit back in. This bike is all original as well. Also, all the others came out without force, like you said, just a push of the finger
 
On things that are stuck use a 50/50 mix of acetone and ATF as a penetrating lube. Spray on, let set. Tap in/out till it loosens up enough to move by finger pressure. It may take a few soaking to free things up but much better than doing unnecessary damage.
Leo
 
JesseeS said:
Leo, before I banged it out the valve was closed completely. I started tapping so it opened a bit, then proceeded to push with no luck, then tried pulling, also didn't budge. That was when I pounded it out. It wasn't when the tip got to the end that it resisted, it was almost as if the valve stem itself had gotten larger. Hopefully i'm describing this correctly, but the whole stem seemed to large for the valve to begin with, maybe why it met with such resistance and will not fit back in. This bike is all original as well. Also, all the others came out without force, like you said, just a push of the finger
Click to expand...

You live in a humid area. The engine sat long enough, without be turned over, that rust/corrosion formed along that one valve stem/guide.

If you had lived in Arizona, that would not likely have happened .
 
A valve with a mushroomed head usually only jams up at that end. You may have a bent valve.
 
Generally a bent valve gets bent between the valve guide and head of the valve. It won't effect the rest of the stem. With it being closed my bet would have been rust.
Leo
 
While we are all speculating on the potential possibilities of causes and factors resulting in an amalgamation of options for the dear fellow….I'll throw my hat into the ring…….

Im going with terrorism….



That or a bent valve thats slightly mushroomed. Maybe it bent a bit first, why it wouldn't come out…….then would resist its natural motion causing it to hammer more on top instead of rolling along the cam and mushroomed a bit too…why it won't go back in.

Bent and mushroomed valve is my second guess.
 
You are all forgetting the other kind of bend that is produced by FOD in the chamber or a guide to stem seizure . That bend , rather than the more common bend between the head of the valve and the valve stem will occur on the exposed portion of the valve stem , above the guide due to side loading of the valve by the rocker arm resulting from resistance to opening .

More likely is burrs on the stem or smeg in the guide bore .

~kop
 
Thanks for all your help guys! To the naked eye, even next to the other valve I dont see anything wrong with it. That being said, I'm just going with new guides and valves. Why screw with it when there's a better alternative. I thank you all, as it was very informative, will keep it all in mind if/when I do another engine build
 

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