Agree with Ace on this one but also before you do that make yourself another little tool. First get an old spark plug and brake all the porcelain off it leaving you with the threaded portion that screws into the head next get a male air line fitting and solder or braze the fitting into the top of the remaining spark plug.Then just get both valves closed, best at the bottom of the power stroke, screw it into the cylinder you want to change the seals on and hook up the air. be careful though if the piston isnt at bottom dead centre when you hook up the air it will probably turn the engine over a little. doing it this way there's no pulling manifolds or heads off because the air is holding both valves up and a lot less trouble. Hope it helps
Yep done this heaps of times on greys with the compressor pumping up the cylinder up with a spark plug/air fitting. It needs to be in 1st or reverse gear and chock the wheels as the pressure can turn the engine over.
As per the advice above to do this without any air pressure in the cylinder DON'T unless you like pulling the head off to get the valve out. If you take the collets out there is nothing stopping the valve from going down into the cylinder
short of a bit of carbon or the like.
Tim