What is this strange clanking sound in the engine ? | FerrariChat
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What is this strange clanking sound in the engine ?

Discussion in '308/328' started by [email protected], Apr 17, 2010.

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  1. andy2175m4@yahoo.com

    [email protected] Formula Junior

    Dec 7, 2008
    473
    Los Angeles, CA
    Full Name:
    Andy Rein
    #1 [email protected], Apr 17, 2010
    Last edited: Apr 17, 2010
    I am converting the 308 from K jet to EFI, and it was running fine a few weeks ago, then I let it sit for a few weeks while I rebuilt the throttle body and rewired the EFI.

    Yesterday I went to start it, and now when I crank the starter, there is this loud clanking sound coming from inside the engine. Before cranking I disabled the fuel pump so it would not run. I made sure it would not start, as the clanking is very loud. It sounds like a small hammer tapping on the block. I checked the front bank, no busted rods.

    This clanking sound seems to be running at 4 times the camshaft speed and possibly 2 or 3 times the crankshaft speed.

    I searched all over the engine with the stethoscope and could not isolate the sound.

    I pulled the timing belt covers and front valve cover and could not see or hear nothing unusual. I pulled the oil pan and could not see or hear anything.

    I put the stethoscope on the starter motor and could not hear anything unusual, but the high speed of the clank makes me think it's the starter drive gear, or something related to the starter, but still no clanking in the stethoscope when I put it on the starter motor.

    Anyone got ideas on what this fast, loud tapping noise is? I came out of nowhere after the car sat for several weeks on jack-stands, not running.

    I also put it gear, held the wheels, and stepped on the clutch, cranked the engine, and the noise persisted.

    TIA for your inputs.

    Andy
     
  2. ramosel

    ramosel Formula 3

    Sep 11, 2004
    1,237
    Meadow Vista, CA
    Full Name:
    R Moseley
    #2 ramosel, Apr 17, 2010
    Pull the plugs. If you turn the motor over by hand (crank bolt) do you hear or feel anything??

    Rick
     
  3. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,876
    Full Name:
    Mike 996
    #3 mike996, Apr 17, 2010
    Do I understand that the engine has not actually been started/running on it's own and therefore we only know for sure that the noise occurs while cranking (starter engaged) and that it may or may not continue with the engine running? I'd pull the starter and inspect it/run it by itself. It's possible that a bad tooth in the gear is causing the problem which would occur at somewhere around the speed you are talking about.

    I don't know the specific EFI and the type of sensors involved but aren't there crank sensor(s) now in place that weren't there before? Is it possible that something in the mounting has slipped and allowed the sensor(s) to be struck by rotating parts?

    Was there any work done that could have caused the valve timing to change? As you know, these are interference engines and if the valve timing is sufficiently off, valves will strike the pistons. Depending on the severity, the valves may just barely hit the pistons.

    Individual valve tapping from excess clearance will produce a loud tapping sound but unless a bunch of them are bad, it would not be at 2-3x engine RPM that you mentioned.

    I tend to think starter-related though the question of "what happened" while it was just sitting is an interesting one...
     
  4. andy2175m4@yahoo.com

    [email protected] Formula Junior

    Dec 7, 2008
    473
    Los Angeles, CA
    Full Name:
    Andy Rein
    #4 [email protected], Apr 21, 2010
    By the way I just wanted to say thanks for your inputs, and tell you what I found. I pulled the starter, and checked it out, it was fine, no problem in the starter at all.

    I then checked the cams and belt timing, and found that the rear bank timing belt had jumped two teeth on the exhaust cam pulley. After I saw that, I re-timed the belt, and the noise went away. I checked the compression on that bank, and no problem. No bent valves.

    Why did that belt jump two teeth on the exhaust cam pulley, I don't know why. It appears it did it while the car was sitting on jack stands, partially disassembled, and not running. I will have to consign this one to the X-Files.....

    Andy
     
  5. Maranelloborn

    Maranelloborn Karting

    Nov 16, 2009
    227
    New York
    Full Name:
    Remund
    #5 Maranelloborn, Apr 21, 2010
    You really need to "replace" the timing belts and tensionor bearings with new ones now that you touched them.
     

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