Question about 2000 GMC Sonoma Extended Cab

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My engine doesnt have any compression

I just rebuilt the engine in my 2000 sonoma and when i tried to start it up it just spins NO COMPRESSION!?!?! Apparently the valves arent closing all of the way. We triple checked the timing before we reinstalled the engine. So other than any possible suggestions as to what the problem could be, I need to know if there is any way to udjust the valves on this particular engine because it has roller rockers. I would appreciate any input you may be able to provide. Thanks

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  • matvic27 Apr 19, 2009

    I want to add that when we fired the engine up it ran great except for 1 or 2 cylinders were missing obviously due too lack of or no compression. I want to add that when the engine was on the stand the compression was fine. When we removed the valve covers after we ran the engine, you could see that when you loosened the rocker arm bolts the spring would decompress at least .020-.030 of an in. So we removed the rocker arm rails from each side and swapped them to see if maybe we had just installed them on the wrong side to begin with. This obviously wasnt the case because the engine has no compression at all now. Cant really imagine why it ran almost perfectly and now not at all. thank yall for your suggestions and comments. They are much appreciated.

  • silver top May 11, 2010

    hi from uk if your engine has hydraulic tappets/lifters ? then this is probably the problem ? your best fix is to remove the lifters then using a vice put each lifter between jaws and slowly compress lifters you will see oil seep out of lifter then when you remove lifter you can compress by hand ? do same to all lifters then reassemble engine start up you will hear a rattling from tappets for few seconds then disapear as oil fills lifters and auto sets to valve clearances this is a common mistake when head gaskets etc are replaced on ohc astras engines as example hope this helps ?

  • mikelbolton May 11, 2010

    Have you done a compression test on it?

    Also, try a leakdown test. That will tell you if it's the piston rings, or valves. So you have a better idea of what to look for before you tear down the engine.

    That link will basically explain the jist of a leakdown test.
    Lemme know what you find.



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I think you should check the timing chain one more time. you probably have the cam out a half turn. did you have the marks both up, or one up one down?

Posted on Jun 09, 2009


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