I've done valve stem seals on N62's a few times now, including a couple times with the engine on an engine stand and have a few little tricks I've learned I want to share with the community.
My first recommendation is a big one and that is to use a clean bungee cord stuffed down the cylinder instead of compressed air. Compressed air prevents you from adjusting the valve height, it opens the possibility of losing air pressure and dropping a valve into the cylinder and it just overall limits your flexibility regarding specific procedures. You also save a spring compression cycle by not using air.
The method for stuffing the cylinder with a bungee cord (or rope) is pretty simple, you will identify a cylinder at BDC and with the intake and exhaust valves that are not about to engage the valve. Let it move up 1/3 to 1/2 of the cylinder and then stuff the bungee cord down the spark plug well, then continue to rotate the engine over until it gets tight. At this point, I back it off about a 1/8 to 1/4 rotation, you do not need - or want - things to be so tight that nothing can move. One of the main advantages of the bungee cord method is that you can actually move the valve down a little bit. And you can move it up, this will be explained during the process below.
I recommend using a bungee cord because it has a little pliability as it is elastic. But rope can work too.
Another tip, if you want to call it that, is to absolutely use the wire brush tools that plug the oil return ports. I've never dropped anything down there, but I have had keepers fall off (usually beacuse the grease wasn't "sticky" enough during installation) and if they fall down there and the engine is installed it's going to be a massive pain in the ass. I probably wouldn't even worry about retrieving them to be honest, the pickup tube mesh is way smaller than the keeper is big, but then you'll have to obtain another keeper and that could hold you up.
You should also plug the spark plugs that you aren't working on with the spark plug plastic tool.
On that note, get a magnetic try or something to set the keepers in. Remove them with the magnet tool and then set them in a magnetic tray until you need them next. You do not want to lose a keeper.
The rest is a step by step guide with some pictures. Sorry they are not all oriented the same way. I will get better pictures next time
Compress the spring, on cylinder 1 and 5 that use the "S" leg, you may need to hold the threaded extension piece into place to prevent it from slipping off the spring
Once it is compressed, push the valve down a little bit (if it didn't go down with the spring). If you can not push the spring down at all, spin the engine in the opposite direction of rotating to relieve the pressure on the valve from the bungee cord
Now that the valve is dropped a little bit, the rocker no longer has pressure on it. On the exhaust you can rotate it out of the way on most of them. On the intake, you'll remove the rocker arm. On the intake side, use a screw drive to hold the lifter in place and just pull the rocker arm up with your hand
Compress the spring more and use a magnet tool to remove the keepers. If the valve drops too much, rotate the engine over in the direction of rotation, this will push the valve up. You can also pull the valve up manually with a strong magnet tool or gently with pliers if needed
Remove both keepers
Next you will decompress the spring fully
Remove the tool
Remove the spring
Use suitable long reach pliers to remove the valve stem seal. On some engines I have had to rotate the stem seal to loosen it, then pull it up - this seems more common on the exhaust side
With the spring out the next step is to clean the area
Use compressed air to clean the area. You can get a rag with a pick tool to clean it if you don't have air, but that is so time consuming. Air compressors are not that expensive, go buy a cheap one at home depot
The valve stem seal seating area cleaned
Install the protective installation cap
Slide the seal over and into place
Remove the protective cap
Reinstall the spring
Reinstall the tool and compress the spring
Compress the spring enough you have access to the reliefs in the valve for the keepers. Use a little grease and stick the valve to your finger (assuming your fingers are long enough). Push one keeper one, rotate it around and do the other. If one gets loose when rotating it around use a pick tool to push it back in place. If it is too low to install the keepers, rotate the engine in the direction of rotation to push the valve up
Once both keepers are installed, I recommend rotating the engine the opposite direction of rotation to allow the valve to lower. Push it down if needed
The reason for pushing the valve back down is to allow you to slide the rocker arm back into place. Once in place, decompress the spring and you are done
The intake side is the same process
On the center seals for cylinders 2, 3, 6 and 7 you will need to insert the tool into this hole
Then install the leg from below
Compress the spring
Drop the valve (if it is too high, rotate engine against the direction of rotation)
On some of the intake seals you can rotate the rocker out of the way. On others, you will use a screwdriver to hold the lifter down and remove the rocker by hand
Use a magnet to remove the keepers
Decompress the spring and remove the tool
Use a magnet as required to remove the spring cap
Use a magnet as required to remove the spring
Use suitable pliers to remove the valve stem seal
Clean with compressed air
Install protective installation sleeve, install valve stem seal, reinstall spring
Compress spring with tool
If required, use a strong magnet to pull the valve up to gain access to the reliefs for the valve keepers. If a magnet does not work, you can use a screwdriver to pry up from the reliefs
Use grease to stick keeper to your finger and install in place, then rotate around. Below shows a keeper installed and rotated to the backside
Install second keeper
Push valve down. If valve won't go down, rotate engine against the direction of rotation just enough to push the valve down
Slide rocker into place, then decompress spring and you are don
You have to remove some bolts and nuts for the oil rail, observe the correct torque specs for reinstallation. Do not overtorque these, especially the bolts. The bolts thread into aluminum and are easy to strip
BMW TIS documentation states: M6: 10 N-m
M7: 14 N-m
M8: 20 N-m
*This image is correct to the best of my knowledge however it is up to you to verify correct torque specs and I am definitely not liable for any damages that occur!
The process is time consuming, but pretty straightforward and being able to easily move the valve up and down via the rope/bungee cord method really simplifies the process. It allows you to easily remove and reinstall the rocker and the keepers. Most of the time, the valves will have the perfect amount of allowable movement if you install the bungee cord, rotate the engine until it is tight, then rotate against the direction of rotation just a little bit (approximately 1/8 to 1/4 of a turn). This allows the valves to drop just enough. You should get a feel for where this occurs.
Put on some good music or put on your favorite movie if you have a garage TV. The process takes awhile - but for me personally, once I do a few I get in the groove of things and just want to keep going. It takes maybe a cylinder to really get a "feel" for it and you don't want to walk away until you are done. Every time I've done this job I've done one bank one day and the next bank the next day.
Overall this is not as bad a job as it seems, but it does take patience. Even with an engine on an engine stand it takes many hours.
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