So I finally got to work on rebuilding my S50 cylinder head, I figured you guys might want to have a look and see how it's going. This will give you a basic understanding of how to remove bent valves from a cylinder head, and how to inspect valves for bending and inspect valve seats for gaps, nicks and other imperfections that will potentially cause the valves to not seal properly.
First off, allow me to introduce you to the pre- procedure to get up to this point. In order to remove valves, the cylinder head must first be removed from the car, this should be done according to the procedure in the Bentley Manual. If you can't follow that procedure, do not attempt this project. Find a reputable dealer or shop to do it for you.
Once the cylinder head has been removed, remove the camshafts according to this procedure.
Again, if you believe you are unable to follow that procedure, do not attempt this project. That procedure is quite delicate and if performed improperly could crack and potentially destroy your camshafts. The E36 camshafts are hollow to reduce rotational mass, but that also means that they are not as strong as they may seem. The force that the valvesprings put on the camshaft could easily break it.
Once the camshafts are out, remove the cam carriers, taking care not to allow the tappets to fall out of their bearings. Once that is done you should have exposed valvesprings. To continue with this project you will need a valve spring compressor that is designed to work on DOHC cylinder heads. most any tool will work, and the one I purchased cost me around $35.
The tool will look like this:
Take care to attempt to grab the spring as low as humanly possible when compressing it and also keep in mind that I had to bend the two inner protrusions inward to actually allow safe contact with the valve spring cap to prevent it from slipping. You may have to as well.
Once the spring has been compressed you will have a tiny little pain in the ass space to work in. BMW's valve spring retainers are two clamshells that fit into grooves cut into the stem of the valve. Their removal will require a pair of needle nose pliers and an awl. Use the awl to seperate the two clamshells and use the pliers to remove them. Once they're gone, the spring and compressor should pull off easily. DO NOT REMOVE THE SPRING FROM THE COMPRESSOR.
Here's what the two clamshells look like (sorry it's so blurry, but my cam sux):
In order to inspect the valve, first remove it from the valve guide. Then hold it up to the light and inspect the edge of the valve seat. It should have no nicks, scratches or carbon deposits on it. Exhaust valves will have carbon deposits pretty much everywhere but the actual seal itself, but keep an eye out for excessive deposits, and if you find them put the valve aside to be cleaned. Assuming everything so far is good, flip the cylinder head over and inspect the valve seat surface on the head. you should keep an eye out for the same sorts of imperfections. If everything so far is good, replace the valve and check to see that a) it rotates smoothly and easily in it's seat and b) there is no wobble or gaps while it rotates. If it passes these simple inspections, the valve is good. All valves with excess carbon deposits should be cleaned. If you don't know how, you shouldn't be doing it. Again, anything you feel out of your depth with in this procedure should be done by a professional.
Visually inspect the valves for bending and imperfections in the seat:
The valves shown here are the two exhaust valves from cylinder number 1, which made contact with their corresponding piston when the crank walked at idle due to the stupidity of the technician assembling the motor. The problem was traced to a failure to properly torque the crank main bearings properly. That's how I got my head at a good price. The valve in the center of the photo is from cylinder number 2, it is perfect and undamaged.
Reassembly is the opposite of disassembly. Keep in mind that the clamshell valvespring retainers are very very very very very very small. They need to be installed with the larger side of their wedge shape facing up. Be careful not to drop them as they are small enough to fit through the oil and coolant passages in the head as well as the head bolt holes and they're a fucking bitch to find if you drop them. The pliers come in very handy here. Our favored method was to put one clamshell on, rotate the valve in it's seat 180 degrees and then install the second clamshell. Then we lift on the valvespring compressor to hold the clamshells together while we uncompress the spring. Before intallation, make sure that both the valvespring cap and spring seat are properly installed. Failure to do so can severely damage the cylinder head and can also cause valve float. Obviously without the valvespring cap, the valvespring won't stay on. Duh.
This photo shows the reinstallation process. Note the grooves on the valvestem where the two clamshells fit on:
Don't forget that having the proper tools around is a massive help:
Oh and btw, the ports on the S50 are already fucking huge, I shit you not, the exhaust ports were big enough for my thumb to fit with lots of room to spare. The intake ports were bigger obviously, and they were gorgeous:
As always, be very careful with all this, and have happy wrenching!