If just twisting your valve around for a while doesn't get it to seat, you'll need to do the following:
When I need to do valves I tend to go ahead and pull the head (if needed) and completely remove the valves. I then inspect the valves for wear and pitting. If the valve is excessively worn or pitted in either the face or stem, I get a different one. If your valve is a 2-piece unit with the head peened on, check to see if the head is loose. If it is, you'll need to heat up and re-peen the thing together. Whenever you do this you will definitely need to reface (grind) the valve in a machine to make sure it will seat properly since the head probably will not peen back on exactly the way it was before it came loose.
Next I make a trip over to the valve grinding machine (your local auto repair garage should have one) and grind a good surface on the valve face (45 degrees works for most old engines). A wet grind machine does best. If you haven't done this before or are uncomfortable with doing it yourself, just ask your favorite auto mechanic to either do it for you or help you do it- it needs to be done right the first time. Often sharing a 6-pack after hours while he teaches you about it works out well.
Then I take a valve seat grinder and polish up the valve seat (I usually do 46 degrees for this- you could alternately do 44 on the valve and 45 on the seat if you wished). Your local garage probably has the seat grinder as well. Same thing for using the equipment- make sure it is done right.
Next I place the valve back into the seat and see if things seat properly. For a proper fit the valve should be flush with the upper edge of the seat, or a bit above it- when you lap it in you should get a scuff mark close to the center of the valve face. If the valve sits too far down into the seat then I replace the valve. Alternatively, you can grind a 30 degree edge into the seat until the valve seats properly, but I do not recommend this if it can be avoided since it will eat down your seat contact area.
To lap in the valve, just do what vern0n stated, and be absolutely certain you get all of the lapping compound cleaned off afterward. You don't want that stuff getting into the moving parts of your engine!
Please note that grinding valves and valve seats removes material. This means your valve spring tension may be affected afterward. You may need to either stretch your springs a little or add a spacer behind them to get the tension back up. This is most noticeable in throttle governed engines where a weakened exhaust valve spring will cause what we've been calling "the 8-cycle problem."
Some folks at this stage will also install valve guide bushings in their engines if they feel it is needed. Any time you install valve guide bushings you will need to regrind the valve seats as well since it may slightly change the angle the valve is being held. These old engines will tolerate a lot of slop in the valve system, and so far I've never had to do this to any of my engines. If you really want or need to install valve guide bushings, I advise you to take it to a professional machine shop.
Hope this helps.
Im assuming some of you take on the task yourselves. I am curious as to how you do it? I know there are special tools for this purpose but I also know some of the brave do this with tools most of us already have laying around. Is it that hard to do? is it worth paying a guy to do it? I have a set that needs doing.......don't mine taking on these kinds of tasks if its within my means.
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Are you talking about refacing the seat area on the valves? or just shortening the other end of the stem to get the correct valve clearance?
Refacing the seat area is usually done on a valve refacing machine that grinds the seat true. They can also be done in a lathe, either way a machine shop is required.
Grinding the end of the valve stem to provide valve to tappet clearance (for example on the small block Kohlers) can be done at home on a bench grinder. Care must be taken to gind the stem square. I clamp a V block to the rest next to the grinding wheel, and use the side of the wheel. Take very small cuts and check the clearance often, one the gap is too big its time to buy a new valve.
An old valve refacing machine waiting for me to get around to a bit of refurbishment:
Just be careful grinding on the side of the wheel, unless you have a cup stone you may wind up with shrapnel in your face. I've seen the aftermath of such an incident and it wasn't pretty...
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Good advice. I "ring" my wheels before using. (If your wheel has a crack, which most likely will be catastrophic, it won't "ping" it will "thud" when you try to lightly ring it like a bell)
Mike you might consider after dressing the wheel, to grind the valve end from the wheel diameter in, using the face of the wheel and not the side. Much safer, and it was designed that way.
If you grind the end too far, you might be able to save it by re-lapping the valve to seat in the block, suction cup style. You should be grinding off very little at a time, so fixing it should be in the same ballpark.
Just be careful grinding on the side of the wheel, unless you have a cup stone you may wind up with shrapnel in your face. I've seen the aftermath of such an incident and it wasn't pretty...
This is very true and generally it is bad practice to grind on the side of the wheel. However in this case you are ususally only taking off a few thousanths, and using a very light touch on the wheel, so I feel comfortable doing it.
Perhaps I shouldn't publicly recommend anyone else do the same though.
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