Cylinder inflation tool?

[Thumper]

I am about to embark on a new valve stem seal replacement with the motor in the truck, and heads on the motor. So I have to hold the valves up while I change them. A buddy used to have a spark plug changed into an air fitting... he could pressurize the cylinders with the compressor, and replace anything with out losing the valves. My question is: should I still rotate the engine to have every cylinder at TDC while I do it? How much pressure would it take to hold the valve up?
Thanks!
Mike

 

[ryoken]

i don't bother spinning it over, i leave the pistons whereever there at.... but you could do it to be safe.. i just don't for the time savings... haven't had one drop on me yet...

i made up a one-way valve fitting that i put on my compression tester hose to do it.. usually i'll bring my portable air tank out to the boat with about 70, 80 lbs in it...

 

[diesel4me]

air fitting...

They sell special fittings with spark plug threads that go on your air hose,but its not really a must have--I usually screw the fittings that "quick dissconnect" on the air hose directly into the plug hole--they are 1/4 inch pipe thread,not 14mm like a sparkplug,but they screw in (finger tight is enough!) and work fine for me just as they are--if you desire,you could bust the porcelain out of an old plug and grind off the ground electrode and tap it with a 1/4" NPT tap,and use that--thats what they sell you as the "special fitting" basically....

Or spend the 10 bucks for a ready made one--I never had too,and I've done 20+ valve stem seal jobs....I've even stuffed nylon rope in the sparkplug holes and turned the engine over by hand until the piston squishes it against the valves--then you KNOW they arent going to drop in the cylinder,and ruin your day,or night!...works without an air compressor too!...