Valve Spring Replace Question?
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Joined: Dec 2000
Posts: 56
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From: Burleson, Texas, USA
Valve Spring Replace Question?
Hello, I need your help! Can I change the valve springs without removing the heads. I heard that you can pump air into the cylinder chamber through the spark plug opening. Is this correct and how many pounds should it be inflated to keep the valve afloat? I am in the process of installing a Comp Cam & figured I should replace the springs also. I assume I can find the fittings at the local parts store to screw into the spark plug opening. Thanks! :confused:
Le Mans Master
Joined: Aug 2000
Posts: 9,662
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From: Semper ubi, sub ubi
Cruise-In VI Veteran
Cruise-In VII Veteran
Re: Valve Spring Replace Question? (DEN78SA)
Keeping them up with air is one way of doing it, the method I prefer uses a thin piece of nylon cord, about 1/4" thick. With a piston at TDC, feed in as much of the cord as you can through the sparkplug hole (of course leave a piece sticking out.) then when you compress the valves there is no way that they can drop down too far. How much you feed in depends on the size of combustion chamber and the thickness of the cord you use. After you change the springs and seals on that one cylinder rotate the engine until the next cylinder is at top dead center and repeat.
Air pressure will work, but it is a sort of a pain in the butt and if for some reason you loose air pressure you can drop a valve (don't ask how I know.) then you have to pull the head.
Air pressure will work, but it is a sort of a pain in the butt and if for some reason you loose air pressure you can drop a valve (don't ask how I know.) then you have to pull the head.
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Re: Valve Spring Replace Question? (DEN78SA)
I have done a number of valve spring replacements on the car and think it is easier then with a head on the bench. I have a spark plug adaptor that allows the air line to be attached to the cylinder. I use full line pressure which is 125 psi. I then have a special tool that goes over the rocker stud and pushed down on the valve retainer. Make sure you do not drop a keeper down the engine on the corners. Also my engines turn over when apllying air pressure so getting a cylinder to TDC is not necessary.
This is not a big deal.
This is not a big deal.
Burning Brakes
Joined: Dec 2000
Posts: 1,183
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From: Des Moines Iowa
Re: Valve Spring Replace Question? (DEN78SA)
I have a small 3/4 h/p air compressor with a 7 1/2 gallon tank, and it has maximum air pressure of 90 lbs. and it worked holding the valves up in my 350 cu in valve spring change, but a larger capacity compressor would have been much better. The small compressors will run during this change operation, and this short 'duty cycle' will result in some water (from condensation) being pumped into each cylinder, so blow the cylinder out after you are all done changing the springs, valve guide seals etc.
