I want to change my valve springs with the heads on the car, so my question is how much air should I pump into the cylinder to hold the valves up? Thank you in advance for any help.

 

If I use air, it's usually in the 50 psi range, but anything there or higher
will work. You don't have to use air, but it makes freeing stuck locks a
lot easier when you have to rap the valve with rubber hammer.

I will be doing the same thing this weekend but w/o the air because I
don't want to remove the plugs. I'll just put each cylinder at/near TDC
as I work on it, and hope the locks are kind to me.

 

Place a socket over the end of the valve and rap it with a hammer before taking the valve spring off to loosen the locks.

 

I dont use air, I use rope. buy some small diamiter rope and bring the cyl close to TDC and fill it with rope then rotate it by hand till it stops, Dont have to wory about air loss or rotating the motor. If you do use air do not take out all of the plugs or the motor will rotate.

 

With plug access so tight, it is a nightmare to do the compressed air method. Bring the cylinder you are working on to TDC and you shouldn't have a problem.