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  1. #1
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    Cold start rattle or pistons clap?

    Hello guys!
    Last summer I made engine rebuild with CP pistons (clearance0.0035") and everything was good.
    But in the winter when it is cold 0C and below, at morning cold start there is a sound like pistons clap,
    when oil gets warm to 50C, the sound disappears.
    The sound isn't so similar to pistons clap, as to an example at Evo9.
    What in your opinion can make such sound? Pistons, vanos, chain?

    November:

    February:

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    those sounds makes me cringe. Don't know exactly what it is but best of luck with a solution

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    Ohh. Dousn't sound too good. This is on a 335i?

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    Click here to enlarge Originally Posted by E90Company Click here to enlarge
    Ohh. Dousn't sound too good. This is on a 335i?
    Yes, this is 335i.

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    Oh god, i din't know what i was expecting but i never want to hear that again

    try talking to your engine builder.. Get that head off and inspected asap, if other things don't work out.. if it's the pistons that's noooot gooood.

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    Does not sound like piston slap, but it sure sounds bad. Piston slap is where the piston rocks in the bore, sounds more like a hollow tock tock lower frequency. Goes away when warm as pistons expand. Your noise is higher frequency like something rattling around under the valve cover or on the front of the engine near the timing chain. Maybe VANOS?

    Have had 2 prior cars with piston slap. One was a new e36 M3, bad batch of pistons came thru production with wrong thermal expansion properties. Knocked like hell (sounded like a cold diesel) until warmed up, complete engine rebuild courtesy of BMWNA, no questions asked. The other was an old Jeep CJ7 V8 I bought supposedly rebuilt engine, developed same exact noise. I took apart the engine and found piston skirts in the oil pan. Oops. I think the guy bored/honed out the block too much and used stock sized pistons.

  7. #7
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    Click here to enlarge Originally Posted by ajsalida Click here to enlarge
    Does not sound like piston slap, but it sure sounds bad. Piston slap is where the piston rocks in the bore, sounds more like a hollow tock tock lower frequency. Goes away when warm as pistons expand. Your noise is higher frequency like something rattling around under the valve cover or on the front of the engine near the timing chain. Maybe VANOS?

    Have had 2 prior cars with piston slap. One was a new e36 M3, bad batch of pistons came thru production with wrong thermal expansion properties. Knocked like hell (sounded like a cold diesel) until warmed up, complete engine rebuild courtesy of BMWNA, no questions asked. The other was an old Jeep CJ7 V8 I bought supposedly rebuilt engine, developed same exact noise. I took apart the engine and found piston skirts in the oil pan. Oops. I think the guy bored/honed out the block too much and used stock sized pistons.
    Stop, stop. Engine block is bored/honed properly, I personally measured everything. All spare parts new, including the crankshaft, rods, pistons etc.
    This sound is only after long parking and in cold weather, but disappeared with warmup. I have run 15000km after rebuild and the car goes perfectly.
    Sometimes I feel small misfires at idle and popping at exhaust. Coils, injectors and plugs is new, compression and leak test is perfectly too.

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    My VANOS corrections, 8.1 intake and 7.3 exhaust.
    Click here to enlarge

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    Are the cp pistons forged? What compression ratio did you go with? Just curious

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    Agree with above that's certainly not piston slap but it does not sound good.
    [02/07 E92 335i 6MT] - Under Construction

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    Click here to enlarge Originally Posted by bmw335iguy Click here to enlarge
    Are the cp pistons forged? What compression ratio did you go with? Just curious
    Forged, CR 9.5.

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    Your car caught the clap! Shoulda wrapped it up. Anyway, this is pretty common on forged pistons. It's a big part of why manufactures don't sell new cars with forged pistons often/ever.

    Could be something else I guess but I doubt it. The cure is a heated garage usually, but not always.

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    1 out of 1 members liked this post. Yes Reputation No
    Fixed! This is Drive Belt Tensioner!
    I had sprayed WD40 on it and the noise was gone!

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    Nice... but still, with forged pistons it's common for slap when cold. Has to do with the composition of the piston being more aluminum and denser due to being forged. They expand much more than cast so clearances aren't as tight when cold. Try to sell a ls1 with forged internals, cam, and aluminum flywheel in Colorado. In a cold day a potential buyer comes, fires it up, and looks at you funny because the motor sounds broken from all the rattle and lope. Ugh.

    OP- may want to replace that pulley. They tend to make that noise before they fail. WD40 sometimes just masks the issue. Just a thought if you have the extra cash, especially if the noise returns.

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    Click here to enlarge Originally Posted by Tomaz Click here to enlarge
    Fixed! This is Drive Belt Tensioner!
    I had sprayed WD40 on it and the noise was gone!
    Wow that was easy!

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    Damn that noise scared the crap out of me. Not something one wants to hear after a rebuild.

    Can you share a bit more info about your build? How does the engine feel with the new internals? Did you change the rods to? Titanium rods would be awesome for improved throttle response.
    E92 335i SB / Black Leather / 6AT / Navi Prof / Sunroof / Active Steering
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  17. #17
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    Click here to enlarge Originally Posted by Tomaz Click here to enlarge
    Fixed! This is Drive Belt Tensioner!
    I had sprayed WD40 on it and the noise was gone!
    Heh good to hear. Bit of a scare eh?

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