replacing valve springs with heads on engine
Thread Starter
Melting Slicks
Joined: Mar 2002
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From: Beringen
replacing valve springs with heads on engine
I was planning on replacing valve springs with a test spring to find valve-to-piston clearance on a new cam. Any idea how much pressure I should put in the cilinder to remove springs with some 260 pounds on the seat ?
Thanks
Thanks
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Spring seat pressure is irrelevant - you don't put any force on the valve during spring removal regardless of spring pressure. You only need enough pressure to support the valve and prevent it from dropping. 20 pounds is plenty.
Burning Brakes
Joined: Feb 2006
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From: AL
you'll never need 60 psig, but that's what i'd set it on for starters. set pressure also depends on how bad valves and rings leak. next, after the rocker arm is removed, use a rubber/plastic mallet to give the retainer a whack just hard enough to separate it from the keeper (doesn't take much). then when you push down on the retainer, it should not "stick" to the keeper. good luck . . .
edit...didn't see scott and lars' posts . . .
edit...didn't see scott and lars' posts . . .
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Remember to put your piston at TDC. if you can get it right at the top it prevents it from trying to rotate the motor over when you run the air in the plug hole. I set my regulator to 40 psi i don't know the conversion to KPa.
260# seat?????? depending on the valve weight you really only need @200 pound seated and @480 open for sub 7500 rpm solid roller cams of under .700 lift to prevent valve float.
260# seat?????? depending on the valve weight you really only need @200 pound seated and @480 open for sub 7500 rpm solid roller cams of under .700 lift to prevent valve float.
Race Director
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From: San Diego - Deep Within The State of CONFUSION!
Le Mans Master
Joined: Apr 2005
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From: Seattle Area WA
Yeah, you probably don't need 100psi but that's what I always use. I just did a seal job on a V-12 and with the funky leverage arm spring compressor that is required, it put a slight side load on the retainer which in turn pushed the valve off the seat. I had a vew valves that fell when I released the retainers but fortunately I had the engine locked at TDC for each cylinder and the valve couldn't fall out of the guide. The last thing I wanted to do was pull the heads on this V-12.
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
The reason I use only 20 to 40 pounds in the cylinder to hold the valve in place is simple arithmetic:
A Chevy 2.02" valve has a surface area of 3.2 square inches. If you put 20 pounds of pressure in the cylinder, you have a total force of 64 pounds holding the valve in place. Since the only force on the valve during spring removal is whatever sideload you get into the spring compressor, the 64-pound force is more than enough to hold the valve during spring removal.
At the same time, the 20 pound pressure is applying a total force of 251 pounds to the 12.56 square-inch piston at TDC. With the piston right at TDC, the engine won't turn over with this force on the piston.
If you put 100 pounds of pressure in the cylinder, this will put a total force of 320 pounds against the valve - way more than needed. But more importantly, it will put a total force of 1,256 pounds against the top of the piston at TDC. If that piston is not exactly at TDC, you stand a really good chance of the engine suddenly turning over when you least want it to. I've had it happen, and you have to go change your pants afterwards.
A Chevy 2.02" valve has a surface area of 3.2 square inches. If you put 20 pounds of pressure in the cylinder, you have a total force of 64 pounds holding the valve in place. Since the only force on the valve during spring removal is whatever sideload you get into the spring compressor, the 64-pound force is more than enough to hold the valve during spring removal.
At the same time, the 20 pound pressure is applying a total force of 251 pounds to the 12.56 square-inch piston at TDC. With the piston right at TDC, the engine won't turn over with this force on the piston.
If you put 100 pounds of pressure in the cylinder, this will put a total force of 320 pounds against the valve - way more than needed. But more importantly, it will put a total force of 1,256 pounds against the top of the piston at TDC. If that piston is not exactly at TDC, you stand a really good chance of the engine suddenly turning over when you least want it to. I've had it happen, and you have to go change your pants afterwards.
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Thread Starter
Melting Slicks
Joined: Mar 2002
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From: Beringen
The reason I use only 20 to 40 pounds in the cylinder to hold the valve in place is simple arithmetic:
A Chevy 2.02" valve has a surface area of 3.2 square inches. If you put 20 pounds of pressure in the cylinder, you have a total force of 64 pounds holding the valve in place. Since the only force on the valve during spring removal is whatever sideload you get into the spring compressor, the 64-pound force is more than enough to hold the valve during spring removal.
At the same time, the 20 pound pressure is applying a total force of 251 pounds to the 12.56 square-inch piston at TDC. With the piston right at TDC, the engine won't turn over with this force on the piston.
If you put 100 pounds of pressure in the cylinder, this will put a total force of 320 pounds against the valve - way more than needed. But more importantly, it will put a total force of 1,256 pounds against the top of the piston at TDC. If that piston is not exactly at TDC, you stand a really good chance of the engine suddenly turning over when you least want it to. I've had it happen, and you have to go change your pants afterwards.
A Chevy 2.02" valve has a surface area of 3.2 square inches. If you put 20 pounds of pressure in the cylinder, you have a total force of 64 pounds holding the valve in place. Since the only force on the valve during spring removal is whatever sideload you get into the spring compressor, the 64-pound force is more than enough to hold the valve during spring removal.
At the same time, the 20 pound pressure is applying a total force of 251 pounds to the 12.56 square-inch piston at TDC. With the piston right at TDC, the engine won't turn over with this force on the piston.
If you put 100 pounds of pressure in the cylinder, this will put a total force of 320 pounds against the valve - way more than needed. But more importantly, it will put a total force of 1,256 pounds against the top of the piston at TDC. If that piston is not exactly at TDC, you stand a really good chance of the engine suddenly turning over when you least want it to. I've had it happen, and you have to go change your pants afterwards.
Ok I get the idea, you guys are right, the spring pressure is not on the valve. I forgot about that. Thanks for all the good info.Anyone can recommend a good valve spring compressor ?
Thanks
Drifting
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From: Oak Ridge NC
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
Le Mans Master
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From: Graceland in a Not Correctly Restored Stingray
Safety Car
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From: Surrey
I did it without any compressed air. Just make sure the piston is on TDC on the cylinder that you're working on (so the valves can't drop all the way in). You can remove/fit new springs (and/or seals) by just pulling up on the valve tip if it sinks down at all (hard to describe but when you're doing the job it's easy to see how). I found the new (umbrella) seals, once fitted, had enough grip on the valves to hold them in place when fitting the springs/retainers. Not having to mess about with a compressor, etc, made the job a lot easier/quicker.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
You can also do it with a piece of rope - done it that way several times: Pull the spark plug out, run the piston down the bore, and cram a bunch of 1/4" rope into the cylinder, leaving the end of the rope hanging out the plug hole so you can pull it back out again, of course. Then, turn the crank by hand (not the starter) and bring the piston back up until the rope gets smashed into the combustion chamber. This will keep the valve in place with no compressed air.