Topic: Tight Intake Valve Shaft?

[Dr. Frankenstein]

I'm working on a '72 CB500 Four, and have the head taken apart cleaning stuff up; the #2 intake valve itself (not the clearance) seems to be very tight to go back into the guide. I've cleaned the guide passageway and the valve shaft itself, and they are spotlessly smooth, but it seems really tight, like it doesn't want to go back in; it'll slide in about a quarter inch and then get really tight, and I haven't tried forcing it.

When I was taking it apart, I had to gently tap it out of its guide...I cleaned them all up and in this case reinserted the valves to #1 and they slid in just fine with no wobble or anything like that, but the #2 intake does not want to go into the guide very easily. The valve does not look bent, and the guides themselves don't look recessed or anything -  Ideas...?   

[Bodi]

I guess you have no history on the engine?
When replacing stock valve guides, they have to be reamed after pressing in as they get compressed by the tight fit. Maybe they have been replaced but that one was not reamed? Or only that one was replaced by someone who didn't know about the reaming requirement?
You do want slight clearance to allow some lubrication and avoid galling/seizing.
You can check for bent stems by rolling on a surface plate or glass if you don't have one. Float glass (normal window glass) is impressively flat.

[Mark1976]

   Check the keeper groove, it can develop a very minute ridge (which needs to be removed) and makes pulling the valve out and reinserting it difficult. Anytime you're tapping a valve out of it's guide ,it's likely you're not doing anything good to the guide. Then check the valve for run-out at the head, I can't believe it's got a bent stem (unless you've dropped it) It's possible, but not likely.

[bryanj]

The valve could be bent due to incorrect fitting of top cover

[Dr. Frankenstein]

Thanks for the tips, I will explore all of them.

Mark, how do you remove that ridge, if indeed it is there?

Bodi, no, I have no history on the engine, but the bike only has 10K miles on it, so unless something catastrophic happened to it in the past - which I doubt because I haven't seen any evidence of that EXCEPT the #3 cylinder was pretty dodgy...and as you can see, #2 as well...IIRC the #3 valve was a bit stiff coming back out too...I got the head off and the cylinder walls are fine though, being smooth and unremarkable (luckily)...but I don't understand how those two pistons got that crapped up because when I got the bike (which had languished outside in a falling-down shed for God knows how many years) all the plugs were in place. As I mentioned, I was able to gently tap the sticky valves out, and the exhaust valves came out okay, but those two intakes took a little gentle tapping.  How do you ream it, and are these reams available? (I would assume they are...) 

Bryan, I don't think the valve is bent due to an incorrect fitting of the top cover...I mean, it could be, but I rolled it on the tabletop and it didn't have a wobble or anything; and as I mentioned, I *think I'm the first person to dig into this engine - but of course I could be wrong/don't know.

FWIW, all the rings are clear and loose except for #3. Before I took the head off, I was able to turn it over with the kick starter for a few turns, but then it bound up, leading me to taking it apart and discovering the difficult valves...this isn't an interference engine, is it?? I didn't see any evidence of banged-up pistons or valve faces...
 

[bryanj]

YES it is an interference engine, very much so
1 is the valve tight during all its movement or
2 only when the top tip enters the guide

[bryanj]

ALSO the colour of the one piston sugests its been stood for a while corroding so the valve/guide could have corrosion as well

[Dr. Frankenstein]

The valve was pretty snug coming out, enough so that I thought it was stuck, but with some gentle taps I was able to push it out. When I tried to test-fit it back In, it seemed that only the top tip met resistance about a quarter inch in - I have not attempted to put it back in fully yet, I don't want to risk damaging the valve guide if I don't have to. I did run some carb cleaner and Q-tips down it, got some dirt out of it and looked into it to inspect the hole with a flashlight on the other end and it looked smooth to me. And actually, I think the dirty brown piston crown is the result of a bug building a nest in there, somehow. I have since cleaned it out and vapor blasted the head. If he managed to crawl in there, that would of course mean the valve was open. What's a good way to clean it?

[Oddjob]

Have you checked another valve in the same valve guide, if it fits ok then most likely a bent valve tip as Bryan says. If another valve fits then I'd suspect rust or deposits on the inside of the valve guide, reaming may fix that.

[Mark1976]

   A picture's worth a thousand words. Uuuum yeah, you may be able too clean that up but I wouldn't consider it a viable path to follow. Soooo much build up and corrosion, ditch the valve and the guide, maybe all off them. Just a thought, your bike/project....

[Dr. Frankenstein]

Well, Stop the Presses...it's amazing what a little application of 1000 grit sandpaper will do...I went out this morning and tried again, and once again it was still tight. I tried fitting a different set of valves (#1, in this case) and they slid in like a new groom on his wedding night.

Applying the KISS principle (Keep It Simple Stupid), I cleaned out the guide with a nylon rotary brush, put a light touch of 1K grit sandpaper on the #2 valve shaft and now they fit fine; Whoo-Hoo...!

Man...! And here I was researching reamers (still might get a set) and valve guide replacement videos...but thanks for the help, everybody!