Originally Posted by Doru

When changing the valve stem seals using the AGA tool, you "can" change the valve stem seals without compressed air, and having the valve you work on resting on top of the piston. That is if you know what you're doing, and being 100% sure you're at TDC. At TDC, without compressed air, the valve rests on the piston. With compressed air it will stick out more. I did this job last year, and I haven't used compressed air on quite a few valves, but I also let air in as soon as I needed the valve to stick higher in order to place the retaining collets. When performing this procedure, you have to be very careful. Also, you have to cover everything up that is around the bank you work on. Absolutely no gaps. You will work with some very small parts and you will handle them with magnets. There are also springs, and small parts that can come lose and fly everywhere if not careful. They could land where you leave gaps, and then it's good-bye in the worst case. The repair procedure should NOT be rushed even if you want to have it done quick. Especially the last cylinder on bank1 & bank2 (close to the firewall) are very taxing on the back, and you might feel compelled to finish it off quick. Big mistake. Just take a break, have a beer (it's summer after all), return later. Take extra care and double & triple check that the parts seat correctly after assembly. You might want a helper after all the stem seals are replaced, to very slowly turn the engine over, so you can inspect every cylinder carefully - the valves & valve guides. the engine shouldn't bind, and the valves & roller guides should move smooth. For the cylinders close to the firewall you need a good small mirror for visual. Same for a few other spots. Actually you should take some pics on how the lifters & guides look prior to starting the job to have as reference.

GL