How much air pressure is needed to change valve springs? Can I use a small air compressor like a 4 gallon 2hp compressor to hold the valves from dropping in the cylinder? Thanks.

 

thats all you need ,about the only kind that would not be enough is the small trunk type compressors with no reserve tank

 

You don't need flow, just pressure unless you cylinder leakdown is huge.

FWIW, a 1.56 dia exhaust valve has about 1.91 square inches of face area, so 100psi air gives about 190 lbs. holding the valve up. You'll probably need more that the seated valve load (120-140#) to break the keepers loose, so a 100 psi-capable compressor should be good.

1.94 intake is about 2.95 square inches, so that shouldn't be a problem.

 

I use a short line close to the compressor with about 120lbs of pressure.

More pressure the better, but don't go over the design capacity for the spring compressor. My buddies shop has 180lbs and it works like a champ.

Bret

 

The only thing I needed when i changed my valvesprings was a drinking straw. I shoved it in the hole for the plug, and used a wrench to turn the motor over. The straw let me feel when the piston was at tdc, and the valve wouldnt fall.

 

So you then push the valves down into the pistons to hold them still while you break the springs loose? Seems like a good way to bend a valve.

 

i always tap the valve retainer with a small hammer before compressing the spring to remove the keepers, a light tap won't bend the valve stem, when you tap it ,keep the hammer in line with the stem...somewhat in line anyways,

 

I'm kinda supprised you didn't have trouble getting the keepers in.

 

Yeah but you have to stop the downward motion of the valve to break the keepers loose even when you tap them to break them loose. Your still pushing the valve head into the piston to stop it's motion. Yeah you can do it that way but holding up the valves with air pressure in the cylinder is a better idea.

Bret

 

Clothesline string through the spark plug hole then rotate the motor until she stops.

I prefer this over all other ways, NOTHING can go wrong. Can change plugs while you're at it too.

 

air pressure to hold the valve up, a light tap to loosen the retainer from the keepers, the valve won't hit the piston, if your hitting it that hard, your hitting it too hard, it only takes enough to disturb the fitting between the retainer and keepers.
way too much time spent on this