Should I lap my valves if I have easy access?

Question

Now that I have my cylinder heads out of my V6 Tacoma, I am considering taking the valves out to inspect them in case they are bent or whatever and grind them. There is no symptoms of valves malfunctioning. They are sealed closed fine. I was just wondering if I should do it since now I have easy access to it? E.g. if I took them out and cleaned them and the housing, will it enhance the engine performance?

UPDATE: What caused me to consider this are the carbon-gunky final segments of the intake passages inside the cylinder head that leads to the valves (what is the proper term for that?) and by looking inside, I could see that the same gunk was collected on the inside of the valve (wide end that actually closes the opening). I cleaned those with a toothbrush sized wire brush and Seafoam. Here is what they looked like:

Dirty:

Clean:

Answer 1

There is an old adage which say something to the effect of, "If it ain't broke, don't fix it." If the valves are sealing fine and look relatively clean, there is no real reason to go through the hassle of doing a valve job. By doing the valve job or even just cleaning them up and lapping them, you may cause more damage than good.

It is, however, a good time to replace the valve seals. If you go ahead and do this, you'll want to check your valves to ensure there isn't a lot of side play in the valves. Realistically, if you can move them side to side, it's probably time to get the valve guides done. If you have to do that, you'll need the valves lapped to get them resealed. You would not be able to do the valve guides at home. In most cases this really should be done by a machine shop.

Answer 2

Will cleaning the valves improve performance? Yes.

Will you feel the difference? It really depends on the present state of the valves but the answer is probably "no".

Is it worth going them while one's in there? That really depends on the end objective and the availability of resources like time and tools.

Just to give an idea of the worth involved, here is a Jafro video which shows how to remove the valves and valve springs from a 4G63 cylinder head.

Here is another one detailing how he cleans the valves and seats.

Answer 3

I would lap them if they don't pass my "gas leak test": plug any other holes in the combustion chambers, spark plug, injectors, etc. then place the head upside down and fill the chambers with gas: if the valves are closing as they should, you won't get gas leak passing through them. I read somewhere about for how many seconds it should be good enough, but I always tried for until gas got evaporated :) If you see leaks below, you need to re lap the suspect valves.