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Thread: 2008 Cobalt 2.2L help

  1. #1
    Forum Member RSWANNABE's Avatar
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    Default 2008 Cobalt 2.2L help

    I bought a Cobalt taking a gamble.

    The previous owner thought it had the normal timing chain issue, but not a broken timing chain. He replaced it and it still had a noise issue so he decided to sell it.

    I bought it, towed it home jump started it because there was no battery in it so I could hear the noise and start to plan what to do next.

    It doesn't sound like a rattle as much as I would think, but a knock, sounds like its up high and someone tapping on the valve cover with a ball end of a hammer.

    Any thoughts or guesses on this? I'm not familiar with these motors or their problems and was only trying to get a back and forth to work car out of it.

    I'm in Roseville in case any of you guys are willing and familiar enough to stop by listen and diagnose this thing with me.

    Thanks a bunch in advance

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    Club Member mikesfastss's Avatar
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    I believe these are interference motors, did he make sure the valves were good after the chain fix
    mike

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    Forum Member RSWANNABE's Avatar
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    Quote Originally Posted by mikesfastss View Post
    I believe these are interference motors, did he make sure the valves were good after the chain fix
    I think he only changed the chain, didn't pull anything apart since nothing broke.

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    Club Member mustangmike6996's Avatar
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    I'd pull the cover and turn it over by hand to look at valves opening and closing (monitor rise/fall distance) to see that one or more aren't bent. It could also be a loose chain guide resonating noise to the cam cover.

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    Club Member Beigg's Avatar
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    how's the oil looking? Does it have a glitter to it? Knock very consistent with rpm? Oil pressure low?

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    Forum Member RSWANNABE's Avatar
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    Quote Originally Posted by mustangmike6996 View Post
    I'd pull the cover and turn it over by hand to look at valves opening and closing (monitor rise/fall distance) to see that one or more aren't bent. It could also be a loose chain guide resonating noise to the cam cover.
    Ok makes sense on all points

    Quote Originally Posted by Beigg View Post
    how's the oil looking? Does it have a glitter to it? Knock very consistent with rpm? Oil pressure low?
    oil looks good, but it looks like it was just changed recently too. Knock is consistent with RPM, not sure on the oil pressure, I'll look next time I start it up.

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    Club Member mustangmike6996's Avatar
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    Quote Originally Posted by RSWANNABE View Post
    Ok makes sense on all points

    oil looks good, but it looks like it was just changed recently too. Knock is consistent with RPM, not sure on the oil pressure, I'll look next time I start it up.
    If the knock is consistent with RPM it's most likely bottom end. Possibly piston slap. If it were much faster than RPM I'd look towards valvetrain. Try a cold dry compression/warmed/ wet (if needed) compression check. How is your pressure?

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    Forum Member RSWANNABE's Avatar
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    Quote Originally Posted by mustangmike6996 View Post
    If the knock is consistent with RPM it's most likely bottom end. Possibly piston slap. If it were much faster than RPM I'd look towards valvetrain. Try a cold dry compression/warmed/ wet (if needed) compression check. How is your pressure?
    I'll double check the rpm to knock ratio, my answer was probably not the best for the question and I see that. I meant its consistent at low rpm, not varying all over. I didn't rev or increase the rpm to see what happens.

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    Club Member mustangmike6996's Avatar
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    Quote Originally Posted by RSWANNABE View Post
    I'll double check the rpm to knock ratio, my answer was probably not the best for the question and I see that. I meant its consistent at low rpm, not varying all over. I didn't rev or increase the rpm to see what happens.
    Something else to check is engine driven accessories. A broken spring g on the tensioner or pulley out of alignment and belt smack can make a similar noise.

  10. #10
    Club Member Beigg's Avatar
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    pop the belt off & run it.

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