Let’s track down a vibration

Discussion in 'Rotating Assemblies' started by DorianL, Feb 12, 2018.

  1. DorianL

    DorianL solid fixture here in the forum Staff Member

    Ok. I just swapped a worn performance cam for a stock cam. The cam had a few worn lobes which I thought were leading to a less than smooth operation.

    Well, I swapped the cam and, what seems like a mild vibration is still there. I think I can hear it and I can see the steering wheel shudder a bit. It feels like it’s slightly out of balance.

    My sense is now, beware of what you suspect more often than not, it can be something completely other. But it feels like something out of balance :D

    So the things is could be:
    - inconsistent ignition
    - worn mounts
    - clutch assy wasn’t properly aligned
    - vibration damper is dead
    - rotating assembly is out of balance
    - accessories and water pump

    How does one check these things ?

    My ignition looks new under there. I’m going to put a temp gun onto my exhaust headers to see if one is running cold.
     
  2. DorianL

    DorianL solid fixture here in the forum Staff Member

    I’m betting motor mounts. All the other rubber is perished.
     
  3. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    well, is it more pronounced sitting still at idle or when driving and does it get changed as the car accelerates, decelerates ,
    when you go into reverse, turn corners, does it change if you use the brakes, etc?
    if your running at lets say a constant 40 mph and push the clutch in and hold it does it change?
    have you checked for loose motor mounts, transmission mounts, ball joints?
    did the damper look worn?
     
  4. DorianL

    DorianL solid fixture here in the forum Staff Member

    Thanks. Lots of tests to try out this weekend !!!

    Will report back
     
  5. DorianL

    DorianL solid fixture here in the forum Staff Member

    I need to put that hood back on and stop that oil leak.

    Say... should I wait 100 miles before changing the oil and the filter ?
     
  6. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

  7. DorianL

    DorianL solid fixture here in the forum Staff Member

    Rgr that.
     
  8. DorianL

    DorianL solid fixture here in the forum Staff Member

    Mmmm. I think I might have found the vibration. There is a visible slight wobble to the lower pulley on the crank. I’ll briefly run the engine tomorrow without the lower pulley. Hopefully it’ll be that
     
  9. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    Last edited: Feb 18, 2018
    DorianL likes this.
  10. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Agreed. I have seen them fail on SBC too. The Death Wobble.
     
  11. DorianL

    DorianL solid fixture here in the forum Staff Member

    The damper seems to be spinning smoothly. The pulley on it is wobbling.
     
  12. DorianL

    DorianL solid fixture here in the forum Staff Member

    If I remove the pulley... is there any way to test the damper to see if it’s the culprit and failing ?
     
  13. DorianL

    DorianL solid fixture here in the forum Staff Member

    I wonder if that also contributed to the leaking timing chain cover ?
     
  14. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    The crankshaft pulley on a Small Block Chevy is pretty stout.
    I do not see how it can bend unless someone had the engine out and the Pulley stuck something hard or was set on the ground hard coming off a Cherry picker engine hoist.
     
  15. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    If you pull the pulley off then there is no good seating area for the crankshaft balancer bolt.
    Start the engine and the balancer make work its way off. Go flying off.
     
  16. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    If you have a timing light hook it up on #1 spark plug wire, shine it at the pulley and balancer.
    See if the balancer hub is OK with the stroboscopic light flashes.
     
  17. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    There are like a zillion SBC balancer styles.
    If you know what year the SBC engine it will help knowing if the balancer is right or not. Confirm by pictures looked at.
    400 SBC is no mistaking for. Its 8 inches in diameter. Has a counter weight on the inside.
    Very thick also.
     
  18. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

  19. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

  20. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Lowest cost options on Summit Racing.
    Made by Dorman. As long as you do not spin the engine over 5700 RPM it should Be Ok stock replacement.

    If the crank pulley is bent you will need the 2 letter code off of the GM Pulley to match up with used replacement.
    Or Find a new match somewhere.
     

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