1990 Maxima
Has anyone replaced the valve seals while the head is still on the engine???
I have only one cylinder seal is leaking.
Compression is still good and even.
Lucky it's the #4 cly that is leaking oil.
Other 5 are fine.
I do plan on changing all seals on that head.

 

valve guide seals or valve stem seals? IIRC the stem seals can be done with the head on as long as you prevent the valve from dropping in the engine but guide seals you're gonna be pulling the heads and going headgaskets/timing belt etc same time

 

Same thing, you can replace the seals with the head on but you need to keep the valves from dropping when you pull the springs. Either compressed air or I’ve seen people use rope. (piston a BDC, feed in as much rope as possible, then turn until that piston is at TDC) Changing the actual seal is pretty easy, twist the old off with some pliers and tap the new ones on with the right socket (lightly tap, it doesn’t take much to seat them.