Once and for all: Morning knocking?
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This is a discussion on Once and for all: Morning knocking? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Ok, this has got me curious. Lately its been cold when I wake up and going out the car early ...

  1. #1
    Registered User Flex's Avatar
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    Once and for all: Morning knocking?

    Ok, this has got me curious.

    Lately its been cold when I wake up and going out the car early in the morning starting up the car brings a slight knocking noise (kinda like a dieseling noise). What in the world is that?

    I know in my old 323 the lifters would tap on cold mornings, but the engine had like 60k on it. Doesnt sound quite the same...

    Any ideas?

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    Most likely it is piston slap. Does it go away after the car warms up? If it does then it IS piston slap. If it does not then you may have a bad bearing.

    TMS

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    Registered User Flex's Avatar
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    Yep. Goes away when it warms up.

    Im going to do a search for it now, but what is piston slap? Bad in any way?

    I've been around cars for a while now but I realize Ill never not be a newb to it all.

    Thanks for the reply,
    Chris

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    Piston slap is very common in subies. I think it is from the very small piston skirts that subaru uses. The piston skirt helps to stabilise the piston in the cylinder bore. When it is really cold the clearance between the piston and cylinder wall gets bigger and lets the piston rock slightly and causes a knock. After the engine warms up that clearance closes up some and the knock stops.
    Just let the motor warm up before you start beating on it and all should be fine. My WRX did this for ~25,000miles with no degrading of performance.

    TMS

  6. #5
    Registered User Flex's Avatar
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    Quote Originally Posted by TheMadScientist
    Piston slap is very common in subies. I think it is from the very small piston skirts that subaru uses. The piston skirt helps to stabilise the piston in the cylinder bore. When it is really cold the clearance between the piston and cylinder wall gets bigger and lets the piston rock slightly and causes a knock. After the engine warms up that clearance closes up some and the knock stops.
    Just let the motor warm up before you start beating on it and all should be fine. My WRX did this for ~25,000miles with no degrading of performance.

    TMS
    Hm, possibly a cause for the slight oil loss seen in many of the EJ20's? Maye small amounts are making it around the rings and burning out.

    I did a search and think its probably the deal. Just bad timing to get cold all of a sudden, I just finished putting in my VF34/injectors at the same time.

    Hope its just the piston slap. havent really had a chance to use the new turbo yet

  7. #6
    Moderating U! KurleeDaddeeWRX's Avatar
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    Quote Originally Posted by Flex
    Ok, this has got me curious.

    Lately its been cold when I wake up and going out the car early in the morning starting up the car brings a slight knocking noise (kinda like a dieseling noise). What in the world is that?

    I know in my old 323 the lifters would tap on cold mornings, but the engine had like 60k on it. Doesnt sound quite the same...

    Any ideas?
    Morning Engine Knock

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    I totaly forgot about the cam tensioner. I talked to a subaru master tech and he said that you could use the old style tensioner with a small modifaction. He acually recomended installing the old style as it is a better design.

    TMS

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    TMS--welcome to our humble abode. looking forward to your posts & wealth of knowledge!
    Vanitas vanitatum...et omnia vanitas

  10. #9
    Moderator Integra96's Avatar
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    Hmm...this cam tensioner has me intrigued. It doesn't get very cold here, but I still get what you guys are talking about once every few weeks since it's dropped into the 40s/50s in the morning. It's very brief, though...maybe 4-5 seconds tops. I also get a high pitched type of humming that only lasts a minute or two also - and stepping on the clutch gets rid of that noise.

    Weirdness. I guess I'll have the dealership check out the tensioner next time.
    "Did you sleep well?"
    "No, I made a couple of mistakes."
    -- Steven Wright

  11. #10
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    Quote Originally Posted by gusto
    TMS--welcome to our humble abode. looking forward to your posts & wealth of knowledge!
    [off topic]
    Thanks.
    I hope you can stand my bad spelling. I really don't have a weath of knowledge. I am just a car hacker at heart.
    [/off topic]


    TMS

  12. #11
    Registered User Flex's Avatar
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    Quote Originally Posted by TheMadScientist
    [off topic]
    Thanks.
    I hope you can stand my bad spelling. I really don't have a weath of knowledge. I am just a car hacker at heart.
    [/off topic]


    TMS
    Ah, Im going to steal that, "car hacker". perfect description of me...sure as **** a tuner

  13. #12
    Registered User ShotgunTC88's Avatar
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    Im callin solid lifters and cold thick oil causing the tap till warmup.


    .02
    Shotgun
    "Speed Kills......But so do Strokes,...Sign your donar card"

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