So it's been awhile since I've actually contributed something real worthwhile on this forum. I figured I was about due...
This will apply more to 16V owners only because we break timing belts all the time and well...our valves don't usually recover.
(this whole tutorial assumes you already have the head off the car)
First assess your head's current condition...
1.)Take the cam(s) off the head to ensure all the valves are as closed as they can possibly be. Making CAREFUL note of which cam bearing goes to which part of the cam. These are generally numbered...just BE AWARE when you put them back in to do it in the same sequential order. 1,2,3, etc
2.) Tip the head back onto the exhaust studs so the intake runners face skyward.
3.) Pour rubbing alcohol down the runners of the head. We'll start with intake first. There are a couple reasons for choosing rubbing alcohol.
*breaks down oil and grease (things we don't need during this process)
*doesn't have the same molecular adhesion (and cohesion) properties water does; think about water riding up the side of a drinking glass; making water a very difficult chemical solution to test for air leaks since water molecules do not want to break their bond easily.
*Is not inclined to cause rust or flash rust.
4.) Leave the alcohol in the head for at least 10min during the evaluation process to ensure the alcohol has ample time to track down around the seat of the valve. So have a beer and watch the valve seats VERY carefully for ANY seepage. If in 10min it's still BONE dry, you're good. If not, if you get even the slightest seepage...you will have a vacuum leak.
MEANING: Poor(er) fuel economy, burnt valves, carbon buildup, poor performance...
NOTE: I recommend you also FEEL around the valve too. Alcohol is hard to see with the naked eye and I personally had a difficult time spotting it.
5.) IT LEAKS! Well...what in the hell do we do now? Be sure you have a good valve spring compressor. Each (16v) valve assembly consists of: a lower spring retainer, an inner and outer spring, a valve, an upper spring seat, and two valve keepers (a split cotter). When you depress the spring the tension is released from the split cotter and you can pull the pieces out with a magnetic tool. Once the cotter has been removed you can pull the spring seat, two springs, and lower retainer. Turn the head and you can pull the valve out from the bottom. This assembly is identical on the exhaust side.
NOTE: MARK EACH AND EVERY valve with a number or some sort of designation so you know what order they go back in. This is very important because you are working with such tight tolerances one valve may not seat the same way as it does in another part of the head (causing a leak).
This is what the tooling assembly looks like:
This is what the valve assembly looks like:
6.) Clean up any foreign debris inside the chamber. Ideally you would use a lacquer thinner or perhaps some sea foam and a combo pressure washing. The idea is you want the carbon build-up and any contaminants out of the seating area(s).
7.) Now that the seats have been cleaned it is time to start lapping
Begin by first wrapping a piece of paper towel around the valve stem. We are doing this because lapping compound can get everywhere and a place in particular it likes to go is into the valve guides...well...this will destroy brass valve guides by loosening their tolerances, in turn causing too much play and poor seating. SO DON'T DO IT UNLESS YOU PLAN ON REPLACING THEM TOO!
Once you have that done, hold the paper towel in place on the valve stem while you guide it into the valve guide on the head. Do not lubricate anything during this process.
Now, put a little dab of lapping compound on the valve itself. You would want to put it in a place where the valve would naturally go to seat/seal.
Push the valve up into the head until you have a little lapping compound oozing around the seat. Turn the head over so you can see the valve stem sticking up. Slide a piece of rubber hosing on the valve stem; 16V heads have 7mm diameter stems, 8V heads have 8mm diameter stems. This diameter will dictate what diameter rubber hosing you need. I chose something that was approximately 1mm smaller in diameter to ensure a snug fit over the stem. To expedite the lapping process I attached an 8x1.25mm stud to my handy-dandy 3/8" chuck Sears electric hand drill and "screwed" the stud down on the hose. (see pic). With everything set up and ready to go, begin "drilling" but instead of pushing the drill into the work, you will want to attempt to pull the valve up through the head. NOTE: This process coupled with the angle of the valve/valve seat will push the compound out of the areas you want finished so occasionally let off the tension, give the valve a chance to ride down the guide so the compound has a chance to creep back into the seat.
This process grinds the two mating surfaces down so they are copasetic with one another.
8.) Pull the valve out. Pull the paper towel out. With another piece of CLEAN, DRY paper towel, wipe the valve and valve seat completely free of rubbing compound. Then, with ANOTHER piece of clean alcohol dampened paper towel wipe the seat and valve down once again. The reason for NOT using the damp paper towel for the preliminary cleaning process is because once this compound gets watered down with other solution it runs EVERYWHERE.
9.) Check your work. Ensure the valve has the same diameter band across the ENTIRE span/circumference. If it does not, it's it's uneven, you have either a bent valve, a bad valve guide (loose tolerance), or a bad seat.
10.) Put the valve back in the head. Put a piece of rubber hose over the valve stem (another piece, one not attached to the drill) and pull. While you are pulling it (pulling the valve into the head) keep a fair amount of tension. Fill the runner with alcohol like you did in step 3-4 and watch for any leaks. If no leaks are found pull the valve out and rub some assembly grease around the valve stem.
NOTE: If you do not put some sort of lubricant on the valve stem you run the risk of it "sticking" until lubrication gets in there (motor oil). If it sticks the cotter can pop out and the valve can drop (literally) causing all sorts of damage
...you are done with that valve and can move on to the next!
If you DO have leaks: lather, rinse, repeat.
Modified by GoKraut at 11:16 AM 7-18-2008