I did a search on how to change the valve springs while the head was on, but didn't find any "how too's"<O</O <O</O So, I thought i would share my experience. This is the first time i've changed the valve springs in anything. My motor is a 1969 chevy 350 block, with 1967 fuelie 461 heads with 2.60 outer diameter valve springs, the springs have a1.75" installed height. Originally the springs were worn or weak, i needed a stiffer opening pressure, and didnt want to mess with valve spring shims, <O</OI decided to use the compressed air method of holding the valves open, because this motor has only 500 miles on it. I figured the valve seats wouldn't leak and they didn't. I've read some info on using a 1/4" nylon rope, compressed against the valves by the piston, to hold the valves open. i would have used the rope method, if the motor had 35,000 or more miles on it. I also removed all of the spark plugs before doing this. <O</OHere is one of the tools i used to connect air compressor hose to the spark plug hole. It's a compression tester hose, one end screws into the spark plug hole and the other end connects to a gage, for compression tests. I used a 3/8" inner diameter fuel line, with a hose clamp to connect the spark plug hose to two 1/4" air compressor tool fittings. then you connect the air compressor hose to that. <O</OAnother tool i needed was a stud mounted valve spring compressor. I got this from <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com</st1:City><ST1Summit</ST1, for around 40/45 bucks, it locks in the down position, that feature is very handy, but it worked o.k. After the metal was stampped for making the tool, it left a rough edge on one side causing the tool to hang up while in the middle of compressing the valve spring. I eneded up taking it apart and filed the rough edges down, wiped all the rubbing parts with anti-seize and the tool worked perfect after that.....nice and smooth. <O</OO.k, we're ready to change a valve spring. <O</O
Bring that cylinders piston to top dead center. <O</OScrew the valve spring compressor tool onto the rocker arm stud all the way down, center the spring lever on top of the valve spring correctly. <O</O
Screw the compression tester hose into the spark plug hole. Connect the other end to the air compressro hose. I adjusted my air compressor outlet pressure to 70 psi, using an in line regulator, (I've heard of people using up to 90psi). Release air pressure into the cylinder, it is normal for the cylinder to leak a lot of air past the rings during this whole proceedure, it will sound way worse that it really is. Also sometimes the motor will spin when the air enter/pressurizes the cylinder, this is kind of normal too, a couple of mine did this and stopped on it owns after two strokes or so, just dont have a wrench connected to the crank when it does.<O</O
Compress the valve spring all the way and lock into the down position. (it will lock on its own) <O</ORemove the two valve retainers from the top of the valve, release he tool from the lock position slowly, and rotate out of the way.<O</O Remove the entire valve spring. I left the valve stems and seal alone....didn;t wipe them off or anything.
Install new valve spring, spring cap and have the new retainers ready. <O</ORotate the spring compression tool back on top of the new valve spring, compress and lock in the down position. <O</OInstall new valve retainers, you have to hold them in there while you SLOWLY release the tool from the lock position, check everything, make sure nothing bent and its done <O</OMove to the next valve on the cylinder, then repeat.... Hope this helps someone......<O</O
I just replaced valve seals using the compressed air method, my pickup has 145,000 miles on it. In all the cylinders the piston was pushed to the bottom of it's travel, good point to mention not having a wrench on the crank bolt. Good tech article.
This is the best way to go for people with a compressor. When I was a kid without a compressor I just stuffed about 3 yards of clothsline cord down the plug hole and hand turned the crank till the piston wadded the cord up against the valves, holdig them in place, and went to work on them.
When your injecting air into the cylinders to hold the valves shut the piston should stay at top dead center the only reason you guys are having your pistons go down is because you didnt have them at top dead center you can rotate your crank until the piston stays up then you wont hear any air passing through hardly at all, unless you have a leak some place That is how you do a cylinder leakage test.
Thanks, man 145,000 using compressed air thats pretty good, this was my first time doing this, my milage number of 35,000+ for using a 1/4" rope was just a guess....thats good to know it can be done on higher milage engines
And the good reason for doing it with the piston all the way up is if something goes wrong the valve won't drop into the cylinder.
This post is way late for this discussion, but here it is any way, in the event some body is doing research. Keep in mind when using the " stuff rope in the cylinder method", that it is possible for the rope to tie itself into a knot inside the cylinder when you stuff it in there. Then you get to learn how to change valve springs with the head off of the engine. Don't ask me how I know this!!!!
I recently change the valve stem oil seals on my BBC, took pictures and did a write up but never got around to posting it. Glad to see someone else had the foresight to show how it can be done. The only thing I did different was to use an old plug wire to hold the valve up. Wound the engine over until it was at TDC turned it back a 1/4, put the plug wire in and then would the engine back towards TDC until the motor 'locked'. Managed to do all 16 seals in about an hour, I only have a crap compressor so even though I had the right tools to use it felt more comfortable using this method. Nice tech by the way. P.
Just wanted to add a small detail. I had the retainers want to stay in the spring cap so when you compress the spring, the valve goes down with it no matter the air pressure. I recommend a good whack with a rubber mallet and maybe a socket to loosen the retainers from the cap before using the compressed air method.
Great tech, I may have to change out the springs on my gmc shop truck this spring. In the past I helped a buddy change the springs and used air pressure to keep the valves up, I did notice alot of leakage during this process. I am thinking of using a rope or something as mentioned to keep the valves up, does anyone have an opinion on this or advice ?
The Jalopy Journal
