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Thread: Rod vs. Valve knock

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    Default Rod vs. Valve knock

    How can you tell the difference between a rod knock and noisy valves?

    I am trying to figure out which problem I have before I go removing the engine.

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    PenisVaginaBoob
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    Default Re: Rod vs. Valve knock

    Quote Originally Posted by eboutin88 View Post
    How can you tell the difference between a rod knock and noisy valves?

    I am trying to figure out which problem I have before I go removing the engine.
    I personally think, valves noise sound like clicking pens, just sometimes a little louder. (my valves make noise too)

    Rod knock sounds like somebody knocking on a counter top.

    At least thats what i think it sounds like.

  3. #3
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    Default Re: Rod vs. Valve knock

    Use a long screw driver, put the handle up to your ear. Touch different parts of the head and cam covers. Listen for where the noise is loudest or at all. Then do the same for the block if ya can, maybe from under the car. You should be able to pick up a cheep mechanics stethoscope at your local auto parts store. This will give you a general idea of where the noise is coming from.
    PLEASE use extreme caution when doing this as you have to lean over a running engine. Have someone else watch out while you work. NO loose clothing
    Rod knock is usually pretty loud compared to valve tic.

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    Default Re: Rod vs. Valve knock

    If you are going to remove the engine, why worry now? Just pull the oilpan, the main caps, and check the bearings. If one is roasted, it'll be rather obvious.

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    Default Re: Rod vs. Valve knock

    My rod knock sounded like a piston was hitting the head at 3,500 rpm - not something I could ignore day after day.

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    Default Re: Rod vs. Valve knock

    valves - sewing machine when in clearance. Valve noise should be .5 : 1 with rpms and starts at idle and just gets louder with higher revs. Other noises will drown this out in higher rpms though. When mine were out of clearance, it made quite the racket/ clatter from 1000-2500rpms or so. I could easily make the noise with the slightest blip of the throttle when at idle.

    rk should be 1:1 with rpms and should be most obvious from 2000-3000rpms. Should not come and go, should be louder when the motors at operating temp (early on set).

    I should add that like the post above, there is no "mold" rk follows. Some have lost oil psi, others say they never saw a drop in psi. Some have it start at 1800rpms and others higher up. A lot of things can knock with so much metal under the hood, grimjacks advice is simplest at this point.

    or IJ's if your not pulling it

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    Grumpy Old Man
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    Default Re: Rod vs. Valve knock

    Get a helper to hold the throttle at the knocking rpm then unplug injectors one at a time, if it's RK it should stop.

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    Default Re: Rod vs. Valve knock

    IJ's advice is probably one of the easiest ways to to verify, another way would be to ground out each plug wire with a test light (hooked to ground) and slightly pierce the wires be careful to not create a hole this will cause the spark to jump. This takes the load off the selected cylinder due to no fire, as with removing the injector clip, there is no forcing of the piston down. Dont quote me but i do believe when you do this and there is still the knocking noise you would have a lifter issue, being that the lifter movement is mechanical and the rod/piston movement is based around ignition in the cylinder.

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    Default Re: Rod vs. Valve knock

    If you've got a mechanic's stethescope (or long screwdriver/baseball bat/broomstick to ear), you should be able to hear very easily whether it's in the top end or bottom end even if you don't know what you're listening for. Put the stethescope (or whatever you're using) to different places on the top end of the engine (valve covers, injectors, etc.), see where the noise is louder. Then go to the bottom end and listen from the oil pan. You should be able to hear where it's louder and where it's quieter at the very least. If it's loudest on top, it's definitely not rod knock. Shouldn't be too hard to tell what you are closest to while testing, and that should give you a good idea of what could be making the noise.

    IJ's injector clip trick is another good way of ruling out rod knock.
    1989 Supra Turbo Targa *sold....*
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    Default Re: Rod vs. Valve knock

    do you not hear it until the motor warms up?

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