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engine knock

Discussion in 'The Hokey Ass Message Board' started by guido`s 40, Jul 14, 2013.

  1. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    Not sure if I am just hearing things or what,but since the motor was freshened this spring I have put about 400 miles on it and today while driving down the highway between 2500_2800 rpm I thought I could hear a knocking noise from the engine. I pulled over and stood next to the motor and a ran it up to 2700 and couldn't hear anything. When I took off back down the highway I could hear it again at cruising rpm,I am not real sure what to think right now. Any suggestions would be helpful
     
  2. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    could be anything. Frozen U-joint.... Look for rust around caps.

    Hows your engine oil look. You runnin the right weight? hows the filter. I had a fram collapse and wipe a crank....

    If it isn't doin it while still but doin it rollin, look at whats movin whien your rollin.....
     
  3. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    thanks I will have to get under it and check it out, the u joints are new and I did just change the oil about 50 miles ago and used a wix filter. I will look around the drive line a little more
     
  4. Engine man
    Joined: Jan 30, 2011
    Posts: 3,480

    Engine man
    Member
    from Wisconsin

    It might be knocking under load. Try a higher octane fuel or an octane booster.
     

  5. J'st Wandering
    Joined: Jan 28, 2004
    Posts: 1,772

    J'st Wandering
    Member

    Or back off the timing.

    Maybe got a bad tank of gas.

    Neal
     
  6. mitchsfab
    Joined: May 20, 2010
    Posts: 99

    mitchsfab
    Member

    Check converter bolts
     
  7. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    Thanks for the ideas. I will slide under it tomorrow and start from the converter and work my way back
     
  8. Sure it's the engine? Could be a tire separating.....
     
  9. 1971BB427
    Joined: Mar 6, 2010
    Posts: 8,717

    1971BB427
    Member
    from Oregon

    Good call! Had a friend call me with same problem last week. I told him to check converter bolts or flexplate, and he found one bolt missing, and two loose!
     
  10. hotrod40coupe
    Joined: Apr 8, 2007
    Posts: 2,561

    hotrod40coupe
    Member

    Maybe somebody is locked in the trunk.
     
  11. GassersGarage
    Joined: Jul 1, 2007
    Posts: 4,727

    GassersGarage
    Member

    A few years ago, we went to the NSRA meet in Bakersfield. On the last day, his Rod developed a knock so he trailered the car home. His son looked underneath and saw the bell housing was slightly separated from the engine. Tighten the bell housing bolts, problem solved. He had installed a new crate motor and was afraid it was bad.
     
  12. saltflats
    Joined: Aug 14, 2007
    Posts: 12,592

    saltflats
    Member
    from Missouri

    What do you mean buy freshened.
     
  13. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    The motor was built a couple years ago but only had about 1000 miles on it so we put new rings and bearings in it
     
  14. saltflats
    Joined: Aug 14, 2007
    Posts: 12,592

    saltflats
    Member
    from Missouri

    Things that make you say HUMM. Did the bearings and rings look bad?
     
  15. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    The bearings looked good the engine had some blow by they tried to run synthetic oil from the beginning we did a leak down test and pulled it apart and had it re honed
     
  16. saltflats
    Joined: Aug 14, 2007
    Posts: 12,592

    saltflats
    Member
    from Missouri

    Correct size bearings I assume, did you at least plastic gauge it?
    Grumpy says the most HP he found on a engine combo that work was to tear it down and hone it and it made more HP if that makes sense.
     
  17. monkeyspunk79
    Joined: Jan 2, 2011
    Posts: 553

    monkeyspunk79
    Member


    Yes sir, I'll bet its something simple like this. Those converter bolts have a habit of being loose or plain forgotten. I hope the motor itself is fine and its a simple fix like this and you're off & running.
     
  18. Engine man
    Joined: Jan 30, 2011
    Posts: 3,480

    Engine man
    Member
    from Wisconsin

    Did you find the cause of the knock?
     
  19. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    I haven't solved my knock problem yet but here is where I am at, I have tried taking some timing out and went to a higher octane fuel and I thought it had quieted down but it really has not. If I rev the engine in neutral to 2500-3000 and hold it there and lightly accelerate or let off I can hear it randomly knock,when driving at cruise speed I can hear it and when its decelerating like going down a hill it knocks. when I hook up the vacuum advance it seems worse, I went from 36 degrees of timing to 32 and changed the curve so it wasn't all in till 3500 and didn't seem to make any difference.starting to wonder about something like piston or piston pin maby?
     
  20. Wrist pins sometimes give you a double-knock, one of those things you have to learn by hearing a lot of sick motors. A header gasket leak can fool the ear as well, look for one of those.

    Try to isolate it to one cylinder by taking off 1 plug wire at a time and see if it goes away or is diminished.

    Bob
     
  21. txturbo
    Joined: Oct 23, 2009
    Posts: 1,771

    txturbo
    Member

    I've even heard a loose belt sound like a knock.


    Posted using the Full Custom H.A.M.B. App!
     
  22. 54Buick48D
    Joined: Jan 25, 2013
    Posts: 208

    54Buick48D
    Member
    from Maryland

  23. Jackson67
    Joined: Aug 5, 2013
    Posts: 29

    Jackson67

    It sounds like it is coming from towards the back of the motor but definitely a knock from top side of motor

    Posted using the Full Custom H.A.M.B. App!
     
  24. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    well I found the problem, I borrowed a bore scope and was able to see part of the top piston ring on the #4 cylinder! looks like I will be tearing apart and try and figure out what went wrong
     
  25. Ohhh. That sucks. Post some pics when it's apart, be interested to see what I looks like.
     
  26. guido`s 40
    Joined: Jan 23, 2011
    Posts: 150

    guido`s 40
    Member
    from nebraska

    well I got a good laugh today I pulled the engine out and started tearing it down got the heads off and all the pistons look fine!! my buddy that had the scope are still trying to figure out what we saw, we both looked at the top of the piston with the scope for several minuets and thought it was clear the top of the piston was broke. After scratching my head and laughing I put everything away for the day and figure I will dig into the bottom end tomorrow and try to figure out the cause of the knock
     
  27. blowby
    Joined: Dec 27, 2012
    Posts: 8,661

    blowby
    Member
    from Nicasio Ca

    Note to self: Make sure nothing is stuck to the borescope lens. :)
     

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