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Technical small block knocking sound on cold start, balancer?

Discussion in 'The Hokey Ass Message Board' started by error404, Sep 1, 2019.

  1. NoelC
    Joined: Mar 21, 2018
    Posts: 2

    NoelC

    I'm no mechanic or frequent poster, but I'll offer my voice to the previously mentioned piston slap. Typically cause by rapid acceleration in a cold engine. Goes away because as the engine warms up the pistons expand. As the piston travels up and down in a cold state rings aren't as tight and the piston tips slightly up the bore. I'm sure a sloppy bore to piston fit could cause the same thing but you mention it was a crate engine? It's not the news I'd want to hear either but my money is betting it's not the round at the front no matter the name attached.
     
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  2. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 271

    ekimneirbo
    Member
    from Brooks Ky

    Try loosening the spark plugs wires on one side of the engine so they make electrical contact but can be easily removed. Start the engine when it's cold and remove the plug wires one at a time and see if the noise stops. If it's piston slap it should go away when the spark is removed. Be sure to use something to insulate yourself from the spark.

    When the engine is cold again, do the other side.
     
    Last edited: Sep 6, 2019
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  3. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,651

    2OLD2FAST
    Member
    from illinois

    Balance shafts were invented and patented in 1904 for inline 4 and v 6 engines...
    If you put a neutral BALANCED damper on an external balanced engine , would said engine be out of balance ??
     
  4. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,143

    gimpyshotrods
    Member

    That would be a person undoing the work of another person. The engine is neither in a state of balance, or imbalance, until it is started, by a person.

    Without the hand of man to animate them, objects are inanimate.
     
  5. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 271

    ekimneirbo
    Member
    from Brooks Ky

    Let me see if I can clear it up for you. You are talking about two different things here. First is just the mechanical balance of an engine. You have to try to get the physical weights of the components to be equal because moving weight creates a force. If you have an equal amount of weight moving in the opposite direction they cancel each other out. Problem is that when trying to save money, oem manufacturers can make externally balanced cranks more cheaply, so they don't do the extra work/cost to make the forces cancel each other. Instead, they place extra weight on the flywheel as a crude way to get reasonable balance. At the other end of the engine they have to also add weight. That's where the Harmonic Dampener is mounted. They simply do the same thing they did with the flywheel and add some eccentric weight at the correct place on the Harmonic Dampener. It's just an existing convenient place to add the weight. So now the Harmonic Dampener is doing two jobs......balancing and harmonic dampening. That's the reason for the confusing terminology......Dampener or Balancer. Now this only applies when you have an Externally Balanced engine.

    On an internally balanced engine the flywheel and the Harmonic Dampener have NO Eccentric weight attached.....so the Harmonic Dampener does NOT provide any additional balance.

    Every engines crankshaft throws flex slightly as combustion occurs. This causes a vibration to happen. If some other component also has a vibration, they can feed off each other and increase until they destroy the crank/engine. Its a very black magic topic, and I'm no expert.....so in layman's terms, these vibrations (harmonics) must be controlled. OEM manufacturers determine at what rpm the harmonics are worst and design the HDamper with a rubber ring tuned to that rpm range. Aftermarket HDamper makers design their units to use fluid inside or small shot inside. That way the HDamper can adjust to any harmonic (vibration) at any rpm.
    Fluid damper has a good site where you can learn more.

    I had a Fluid damper once for an Externally balanced 400 Chevy small block. The actual name is "Dampener" but it's just easier to say "Damper" because it "dampens" the harmonic vibrations.

    Hope I cleared things up for you.....now you can think about this while you try to sleep. You see, I do that too.
     
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  6. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,651

    2OLD2FAST
    Member
    from illinois

    This has all the trappings of one of those smoked up late night college dorm discussions where everyone is trying to prove how smart they are ,didn't make sense or prove anything then either ...there's a huge gap between common sense and theoretical sense ,some of us dwell in reality , others , not so much ...
    This is in response to post 64.....65 makes reasonable sense.....thanks Mike Obrien.....
     
    Last edited: Sep 6, 2019
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  7. error404
    Joined: Dec 11, 2012
    Posts: 110

    error404
    Member
    from CA

    I found a few videos of piston slap, and some of them do sound very similar to what I have. I'll give this a try, thanks!



    I'm not going to rule out the chrome pulleys on the front of the motor yet until I get a free weekend morning to remove the belts and give it a try.

    Someone here suggested putting the transmission in drive and holding the brake, loading up the converter a bit to see if it goes away. I did that, the noise didn't change.
     
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  8. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,472

    Boneyard51
    Member

    If it’s piston slap, loading it through the converter, would likely increase the noise!







    Bones
     
  9. Piewagn
    Joined: Mar 25, 2009
    Posts: 613

    Piewagn
    Member

    Skirt slap! I worked for GM for 30 years, those small blocks were notorious for piston noise. Let me guess, it goes away after it warms up.....right? My old truck had that noise, drove the piss out of it and never had any issues. Only that it was annoying......
     
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  10. @error404, so the weeken is done...what happened with the belts off? Did it make any difference?
     
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  11. Flatrod17
    Joined: Apr 25, 2017
    Posts: 9

    Flatrod17
    Member

    In that short video I see the damper moving front to back. I think there is a thrust problem and you are hearing the chain rubbing the front cover. Check crank end play with a pry bar. But really that sound should not go away after a few minutes.
     
  12. Such fun ....... :) .

    I think it sounds external .

    Water pump bearing or alternator bearing dry and ticking ....... ?
     
  13. Desoto291Hemi
    Joined: Apr 21, 2009
    Posts: 655

    Desoto291Hemi
    Member

    Sounds like the timing chain making contact with the cover.
    Get an engine stethoscope and place the probe against the timing cover when you first start it,,, I think you will hear it clearly.

    Tommy
     
  14. 6sally6
    Joined: Feb 16, 2014
    Posts: 691

    6sally6
    Member

    They call it "belt-flapp'in" in Alabama.
    6sally6
     
  15. Tooth
    Joined: Nov 5, 2016
    Posts: 107

    Tooth
    Member
    from Missouri

    I once built a 331 small block Chevy Stroker motor, and ran fine for a long time and then it developed a knock. I too thought it was piston slap. So I started taking the belts off and my step dad asked me to move my car. I started the car up with the belts off and the knock went away. Turned out it was the water pump! Just saying, put a new water pump on it and no more knocking noise and it only done it when it was cold. Good luck and I hope you find the problem;)
     
    Last edited: Sep 14, 2019
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  16. bschwoeble
    Joined: Oct 20, 2008
    Posts: 397

    bschwoeble
    Member

    Hey Ekimneirbo, thanks for the explanation. Very well done. I learned the purpose of a harmonic dampener back in high school auto shop (61-63).
     
  17. HotrodHR
    Joined: Jul 12, 2010
    Posts: 181

    HotrodHR
    Member

    So did we come up with the source of the noise? In the video the noise sounds very mechanical, metal to metal, clicking... try the taking off belt step, check the water pump, alternator, and recheck the flex plate for cracks. I had a 1969 Pontiac wagon with v8 automatic that developed a metallic sounding knock, grind sound. It ended up being a crack just outside of the bolts almost all the way around.
     
  18. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,219

    sunbeam
    Member

    Does the truck have a heat riser valve?
     
  19. error404
    Joined: Dec 11, 2012
    Posts: 110

    error404
    Member
    from CA

    Ok, I've got an update.

    I pulled the belts this morning, and fired it up. ZERO noise. :)

    I put the belts back on, fired it up again, and still ZERO noise. Possible one of the belts wasn't tight enough? They seemed tight, but maybe they weren't tight enough.

    It's also possible that it wasn't cold enough for long enough last night, as it was almost 100 degrees yesterday. But it's been doing the noise every morning since I got the truck, so that leads me to believe that it might have been the belts not tight enough. I'll give it another try tomorrow morning, it's not supposed to be so hot today.

    I'll report back when I give it another try. HOPEFULLY it's just the pulleys. :)
     
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  20. error404
    Joined: Dec 11, 2012
    Posts: 110

    error404
    Member
    from CA

    Thanks everyone who replied, I'm confident I found the noise.

    It was 50 degrees last night, fired up the motor in the morning to drive to work, and again, ZERO noise! :)

    That's 3 mornings in a row without the noise, where previously it would make the noise every single morning. So it looks like it was a loose belt.

    The belts didn't seem loose to me, but apparently that's what it was. I don't understand how belts/pulleys make popping noises like that, but apparently they can.

    Now that that's solved... on to all the other rattles and squeaking noises from the body... haha! I have a feeling that every few weeks or so, I'm going to have to go through and tighten all of the wood screws holding the sheet metal to the wood interior.
     
    Last edited: Sep 17, 2019
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  21. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,472

    Boneyard51
    Member

    In my years of working on cars, I’ve heard belts make every kind of sound there is! Glad it was a belt!





    Bones
     
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  22. Three pages and 80 replies to fix a loose belt!?!? I would have held that sucker to the floor and slun that offending belt off or sumthin. LOL
     
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  23. spanners
    Joined: Feb 24, 2009
    Posts: 792

    spanners
    Member

    You know, I nearly would've bet money on it being the doohickey that goes to the flux capacitor.
     
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  24. error404
    Joined: Dec 11, 2012
    Posts: 110

    error404
    Member
    from CA

    the first thing I did was squeeze the belts, and they seemed tight to me, so I figured that wasn't it. sometimes it's the simple things that I overlook, haha
     
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  25. BLAKE
    Joined: Aug 10, 2002
    Posts: 2,747

    BLAKE
    Member

    Didn't read all the previous replies, but before going too deep, try thinner oil. My nailhead did this when I ran 20w-50... went away with 10w-30. Lifter tap, I presume.
     
  26. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,472

    Boneyard51
    Member

    Sometimes tightness is not everything that cause belt noise.
    Many moons ago while working at the City garage, we got a police car that came in with a “ knock” that sounded just like a rod! We didn’t think it would last long enough to get parked and diagnose. Oil and pressure ok! .....noise was coming from the front of the engine( I could hear back then), sprayed some “ belt dressing” on the belt....knock would disappear!.....then come back in a few minutes. We adjusted the tension on the belt....no help. Took belt off, could find no obvious problems with the belt, put a new one on ....no noise! And that sounded like a rod was fixing to come through the block! Not just a squeak or a tap!
    That’s belts for you!





    Bones
     
  27. If it is only occurring when the engine is first fired up, and doesn't happen at any other time, it could be a lifter that is slightly under adjusted and is slow to pump up. I have had a similar problem when the lifter wasn't adjusted to the middle of the range.
    Like others have stated, I have experienced an exhaust leak from a worn header gasket, that disappeared when the engine was warmed up. The flange material on the headers of one of my engines is thinner, or at least they deform more easily, and it requires that I replace the gaskets anytime I remove the header or headers.
    As for the balancer, the only possible point of failure on a balancer, is the breaking of the bond between the flexible material and the inner body or outer ring. Normally when this happens, the timing mark will be displaced from the proper position. I have never heard of one making a knocking sound. I have never seen a loose fit between the balancer and the crank, but it seems to me that any sound from this problem, would not go away when the engine was warm.
    Another way to trouble shoot this problem, would be to have the engine running, and pull the spark plug wires one at a time to see if the noise stops. That would probably eliminate the wrist pin as a cause of the problem. There would still be compression in the cylinder, but if it is a knocking sound, removing the ignition would possibly be enough to eliminate the knock.
    Bob
     
  28. Doublepumper
    Joined: Jun 26, 2016
    Posts: 413

    Doublepumper
    Member

    I had an El Camino with a 350 in it that made all kinds of noise from the belts. I'd replace the belts and it would be fine for about a week, then start squeaking, squealing, popping and making weird noises again. I tried belt dressing and that didn't help. Finely, I pulled the pulleys and bead blasted the grooves. Re-installed them and no more noise. Thinking the slick surface of the grooves and the physical placement of the pulleys was causing a resonance to be developed once the belts had gotten burnished smooth and were entering and exiting the slicked up grooves....dunno.
    I've had engines with chromed pulleys that didn't make belt noises, so go figure.
     

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