Valve Clearance Adjustment
This is something of a maintenance thing more than a performance thing. Valve clearance issue can improve your fuel trims and also make the engine less noisy. Loose valves tend to be louder and tight valves tend to be silent. However silent valves/engine doesn't necessary mean a good thing. If you tighten the valves more than spec, this can lead to valve burning up and getting damaged. It is usually preferred to have slightly loose valves than tight ones.
I have been facing negative fuel trim issues since I got the car and it has been difficult to diagnose it. However given the fact that I have deleted the resonator and I use a high flow air filter, thats why my fuel trims will be slightly off than oem spec since I am not running oem parts to be exact.
Anyway so I went ahead and got the valve clearance done last November from a reputable workshop dealing mostly in K series engines. What I realized is that there is a huge knowledge gap on this topic between the mechanic and the actual procedure. Most mechanics dont follow spec and even if they do their technique is just strange. For eg the mechanic I went to wanted to do the intake and exhaust valves the same value of 0.01 inch. This is not true for K series engines.
The other thing he did was he placed the feeler gauge between the cam lobes and claimed that this is just how he did it and its the same as placing it under the valve clearance adjustment locknut.
After much contemplation and discussion with friends and viewing several videos and reading up on it I decided to go ahead and do it myself. The biggest reason why I wanted to do it is that its supposed to be done on a dead cold engine. This is extremely difficult to achieve at a workshop in a few hours especially in summers. Unless you leave the car overnight and the mechanic works on it the next day, the only feasible option is at home.
Anyway I went ahead with it and the fuel trims improved slightly however they are still a bit negative. The engine sound is much smoother although you can still hear the valves which is totally fine. Honestly the biggest thing is that I sleep peacefully at night knowing the valves have been adjusted as per spec and I personally double triple checked each and every one of them.
Needless to say almost all my valves were out of spec from the job done by the mechanic. Mostly they were loose on the exhaust side and a few intake ones were very tight.
K24 specs:
Intake: 0.21-0.25 mm (0.008-0.010 in.) Exhaust: 0.25-0.29 mm (0.010-0.011 in.)
K20 specs:
Intake: 0.21-0.25mm (0.008-0.010in.) Exhaust: 0.28-0.32mm (0.011-0.013in)
Tools: 45 degree feeler gauge, 10" combination wrench, good quality flat head screw driver, a 19 mm socket with extension attached to the crankshaft bolt, 16mm deep socket to remove plugs
You can find procedures online so I wont mention any details but rest assured this is not for everyone. The difficulty level is a definite 10/10 because of various reasons. The valve clearance adjustment itself is probably intermediate level. If you do a basic tuning yourself like changing plugs, cleaning throttle body etc then the valve adjustment is a DIY for you. You just need to make sure the feeler gauge has just slight drag on it and its not getting stuck or completely loose. The other tricky bit is setting down the valve cover gasket properly and applying just small amounts of silicon. Usually mechanics love overloading the silicon sealant.
The biggest difficulty is the position of the exhaust valves. Physically its difficult to get all the way back there and your back and legs get a pretty intense battering. Ideally a third hand would have been amazing. I did it all alone and holding the wrench in place, adjusting the screw with a flathead screw driver and also sliding the feeler gauge simultaneously was a big challenge.
Anyway I am posting some youtube videos of the actual adjustment on the intake valve side (which was much much easier than the exhaust side) and a sound comparison video. Enjoy and feel free to ask questions!
Sound comparison
Valve adjustment
Some pics:
