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Thread: 1987 Chev - Cylinder compression after valve stem seal replacement on 350 tbi

  1. #1
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    1987 Chev - Cylinder compression after valve stem seal replacement on 350 tbi

    I just replaced the valve stem seals on my 350 tbi and I am bothered by something. Before I replaced the seals, I had 175 psi on all 8 cylinders. After changing the seals, I am getting 175 psi on all cylinders except the no. 1 cylinder. It is now at 155 psi. I have adjusted the valve lash so I know its not too tight which wouldn't let the valves open. It is different than the others though.

    With all other cylinders, I turned the push rods while tightning the rocker nut until I felt it stop and then went another 3/4 turn. With the no. 1 cylinder I did that innitailly and got no compression so the valves weren't open. I kept loosing them a little at a time until I felt like they were way too loose and I can get is 155psi. The only way I can get 155psi is with it loose and I can turn the push rods with my finger so I know it will rattle when I crank it up and that won't work either. Does anyone know what might be wrong? All cylinders were strong before the seal change.
    Last edited by crabtruck; 03-30-2011 at 08:13 PM. Reason: title

  2. #2
    Senior Member 87c10slammer's Avatar
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    perhaps there is a peice of carbon or something in the valve seat. worse case is you bent the valve when you were doing the head job and will need to take that head back off and replace it. try taking the rocker back off and gently smacking it with a hammer a few times. it could be eather valve on that cylinder that is messed up so i would check both of them out.

  3. #3
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    If you have it to tight the valves won't close, not the other way around. loosen it up, fire it up and see what happens.
    Joe
    89 K2500 Chevy, Wee-Oh-five 294K miles
    1962 Scout 80 parts I guess
    1966 Scout 800 resto job
    2005 Chevy 2500HD Short cab long box DURAMAX
    1996 P30, 6.5 NA Mac Mobile
    whole lot of buicks

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    Quote Originally Posted by 436'd skylark View Post
    If you have it to tight the valves won't close, not the other way around. loosen it up, fire it up and see what happens.
    Yeah that's what I meant but I still am concerned about the problem. The motor is out right now and if I needed to do a head job now's the time. It just bothers me that it was fine before and not now.

  5. #5
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    have you run the motor since setting the valves?
    Joe
    89 K2500 Chevy, Wee-Oh-five 294K miles
    1962 Scout 80 parts I guess
    1966 Scout 800 resto job
    2005 Chevy 2500HD Short cab long box DURAMAX
    1996 P30, 6.5 NA Mac Mobile
    whole lot of buicks

  6. #6
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    Quote Originally Posted by 436'd skylark View Post
    have you run the motor since setting the valves?
    No I haven't. Its not in the truck right now.

  7. #7
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    I would bet thats your problem then. the lifters have probably collapsed and bled out.once you run it for awhile they will pump back up and you will be fine. the number 1 cylinder is furtherest from the oil pump, thats why you are having these issues.
    Joe
    89 K2500 Chevy, Wee-Oh-five 294K miles
    1962 Scout 80 parts I guess
    1966 Scout 800 resto job
    2005 Chevy 2500HD Short cab long box DURAMAX
    1996 P30, 6.5 NA Mac Mobile
    whole lot of buicks

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