Replacing Valve Seals without Removing Head?

[savatreatabvr]

I've heard the best way to replace the valve seals without removing the head is to use compressed air, that works great if the cylinder doesn't leak. But isn't the reason valve seals are replaced in the first place is because they're leaking? An old old timer told me the best way yet, he said remove the plug, bring the piston to TDC and stuff the cylinder with 3/8" rope and the valve will not drop a fraction of an inch! When done replacing the seal just pull the rope out and move onto the next cylinder! I tried it and it works great! Be sure and spend a few extra bucks on good quality spring compressor, I almost lost some teeth when my cheap spring compressor broke and the spring came shooting out like a bullet! Got my attention!

[gearheads78]

You still have seal in the camber. The leak is around the guide so nothing to worry about there. Ive done it plenty of times both ways but I prefer the air because its faster.

[406 Q-ship]

The valve seals will not cause a pressure leak from the cylinder, just for oil to leak down the valve into the cylinder. Unless you have one weak a$$ compressor it will keep the valves up even in a engine with poor valve seats (burned valves not with standing).

I have always done the blowing in air to the cylinder when changing springs and valves seals I only do it with one change over the normal. There are going to be people who say it will not work but it does just fine. Remove the pressure completely off both the intake and exhaust rockers and then apply the pressure into the cylinder, the engine will rotate putting the cylinder at BDC, while holding the valve closed (there is better ring seal at the bottom of the cylinder too). Change the springs or valve seals and reinstall the valve retainers, readjust the rockers and your done. This eliminates the need to get the engine exactly on TDC.

[savatreatabvr]

So can I replace the seals and guides at the same time with the heads on the motor?

Originally Posted by gearheads78

You still have seal in the camber. The leak is around the guide so nothing to worry about there. Ive done it plenty of times both ways but I prefer the air because its faster.

[donut]

Seals yes, guides no, afaik, a machine shop will have to do guides.