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why is my engine knocking?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Blazer-Boy, Oct 3, 2002.

  1. Blazer-Boy

    Blazer-Boy Registered Member

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    my '72 has a rebuilt 350. there is a knocking or clicking sound coming from my driver side valve cover. i havent taken the cover off yet. i wanted to know if anyone knew what the problem might be before i took it off. any help or advice would be greatly appreciated.
     
  2. Roostr84

    Roostr84 1/2 ton status

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    The first thing that comes to my mind is a rocker arm. But it could also be a lifter. Yo don't have fuel injection on your rig do you b/c sometimes injectors are noisy too.
     
  3. jeffro

    jeffro 1/2 ton status

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    I'd pull the cover on the noisy side and look at the valve train. The lock nuts on the rocker arms could be worn out, They don't last forever.
     
  4. Blazer1970

    Blazer1970 1/2 ton status

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    Are you sure it's not an exhaust leak?
     
  5. Blazer-Boy

    Blazer-Boy Registered Member

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    well... i'm pretty sure that its not an exhaust leak. i've had plenty experience with those. a couple friends of mine say that i might need to tear it all apart and look at the crank. they think i might need new bearings. i was hoping to avoid this...
     
  6. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    When mine made that noise, it was a broken rocker stud....with the rocker laying in there loose.

    Fortunately, the broken part of the stud didn't find it's way to the bottom of the engine, so I replaced the broken stud, and set the lash and was back on my way.

    Usually a broken intake will just make a clicking sound....a broken exhaust will backfire through the carb (since the gasses going into the cylinder cannot get out)

    I'd say pull the valve cover off ASAP, and see what's going on....it's probably going to be something obvious. The longer you wait, the more you are inviting BIGGER trouble.

    You can run the engine with the valve cover off to locate the noise, but it will be messy. Those little rocker "clips" are pretty useful for keeping the spraying oil contained.....

    /forums/images/graemlins/cool.gif
     
  7. chulisohombre

    chulisohombre 1/2 ton status

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    eagle river huh?im originally from fairbanks.more than likely a loose rocker.its easy to adjust.you might as well adjust them all.let engine warm up for a few minutes.take off one of the valvecovers.start the engine.then start from the front and loosen the first rocker till it starts tapping.then tighten slowly till it stops tapping.then turn it in 1/4 turn increments until you hit 3/4 of a turn.then go on to the next one.like grag said this will be a messy job.if you cant get the tabs then you can use a cutout of cardboard to fit in to catch the oil splatter.good luck nad hope to help a fellow alaskan. /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
     
  8. Blazer-Boy

    Blazer-Boy Registered Member

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    okay... i drained my oil last night just to see if there were any metal filings or shavings. i was relieved to find that there werent any. so today i'm gonna take of the valve cover and root around in there. thanks for the card board cutout tip. well from the replies, its definitely sounds like it might be the rocker... thanks for the all assistance. you guys sure make it alot easier to work on trucks. i'll let you know what i find...
     
  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    We've all had to learn from someone.....

    I didn't know anything about Blazers 2 years ago, this list (and it's members) have taught me LOTS already.
     
  10. Blazer-Boy

    Blazer-Boy Registered Member

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    alright... i took the valve covers off and started up the beast. i checked the rockers and they all seemed to be tight. after taking off the covers though, the knocking sounded like it was below the rockers and maybe even towards the middle of the engine... i just scratched my head and cleaned up all the oil. back to the drawing board...
     
  11. J.Lance

    J.Lance 1/2 ton status

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    Doesn't sound like a happy place. How many miles does the rebuild have. Sounds like you could have spun a bearing on the crank. Next step is to pull the oil pan and check it out (unfortunately). I had a buddy who had a rod knocking and it turned out that the tack weld for the oil pump pick up tube had broke and the tube was clunking around with the crank. Nothing serious. Hopefully your issue isn't too bad. Once you get the pan off, take off a couple bearing caps and check for scoring, heat marks, cracks, etc on the rod bearings. Good Luck. /forums/images/graemlins/confused.gif
    I had a friend from Eagle River, Tyson Roberts ring a bell?
     
  12. Roostr84

    Roostr84 1/2 ton status

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    If the clearances were all good then I would have to say a bearing as well.
     
  13. chulisohombre

    chulisohombre 1/2 ton status

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    did you actually try amd adjust them like i stated.you cannot tell just by looking at them if they are tight.the lash only lets them sit so that they are tight enuf to keep the drivetrain tight and the pushrod seated in the lifter tightly.if it is the slightest bitloose from where it is lashed correctly it will make noise.i just adjusted mine recently because of a couple valves tapping i had on one side.now it runs much better with no abnormal noises.hope your engine turns out alright if not the rockers.like i said its the easiest thing to try to fix the noise.it is easy to do and only takes a couple of minutes per side.
     
  14. Blazer-Boy

    Blazer-Boy Registered Member

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    i did actually adjust them. i was really hoping that this would fix my problem. the frontward most rocker nut was a little loose (this is where i thougtht the noise was coming from). i tightened it, but it still makes the noise. i was going to loosen it a bit more, but i didnt know what would happen if i loosened it too much. no amount of tightening really affected the noise... /forums/images/graemlins/confused.gif
     
  15. chulisohombre

    chulisohombre 1/2 ton status

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    maybe the lifter is gone then.i blew my oil pump out on the highway and 2 of the lifters froze which is why i stopped because the engine was making noise.guess you will have to tear into the internal then.sorry to hear that it wasnt an easy fix.maybe also the cam lobe on that valve is flat.ive heard of that happening on aftermarket cams.if you haVE a warrantee i would take the engine back.i cant remember if you said this was a new rebuild.been a while since i checked your post for this.hope you find the problem.looks like anether rebuild is in order with new parts.then at least you know it is done right
     

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