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Projects Rod knock?

Discussion in 'The Hokey Ass Message Board' started by Italianjbond, Apr 4, 2020.

  1. Italianjbond
    Joined: Mar 2, 2020
    Posts: 7


    I have a motor I just recently got and got running again. A 69 351w. 10.5 compression. I finally got it running but I have a knock in it. At idle there is no knock. If I hold it at a higher rpm I hear nothing for a couple seconds then I start hearing what sounds like a rod knock.

    My understanding is you always hear a rod knock it doesn’t go away. But this one come on like I said. And disappears at idle.

    Any clue?
    loudbang likes this.
  2. Budget36
    Joined: Nov 29, 2014
    Posts: 3,474


    And the oil pressure pressure is?
    loudbang, VANDENPLAS and Deuces like this.
  3. sliceddeuce
    Joined: Aug 15, 2017
    Posts: 2,982


    We need pics.
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  4. Deuces
    Joined: Nov 3, 2009
    Posts: 18,565

    from Michigan

    Start replacing bearings and a new oil pump...
    loudbang likes this.
    Joined: Dec 14, 2009
    Posts: 2,379


    93AF1EEA-2E3E-43A4-AEC2-5D27A86EFBEB.jpeg Check your oil pressure
    Fuel pump possibly
    Balancer separating ?
    Auto or manual trans?
    Torque converter bolts loose?
    Oil filter collapsing ?

    rod knock is a pronounced loud hollow knock that’s rhythmic and follows rpm
    Like a hammer hitting a steel beam.

    what did you do?
    How long was it sitting?
    How long have you run it?

    more to the story please.

    but one of those cheap mechanics stethoscopes and poke around see if you can find the source of the sound?
  6. manyolcars
    Joined: Mar 30, 2001
    Posts: 8,276


    dont run it until you plastigage it. The crank may be ok but if you keep running it, it wont be
    firstinsteele, loudbang and Deuces like this.
  7. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 24,940

    Jalopy Joker

    where did you get motor from? whoever you got it from still around to get info on it?
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  8. Italianjbond
    Joined: Mar 2, 2020
    Posts: 7


    Psi is 40 at idle. Seems to have a high flow pump. Sounds like it’s in the front of the motor as well.

    Sent from my iPhone using The H.A.M.B. mobile app
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  9. TA DAD
    Joined: Mar 2, 2014
    Posts: 185

    TA DAD
    from NC

    idle it up where it knocks and remove plug wires one at the time and you can usually determine which cylinder is knocking. Turning the timing back can quiet it also. No one has ever bought a car with a miss in it and find a plug tapped shut ? open the gap and now it knocks
    CobraJoe, loudbang and deathrowdave like this.
  10. hotrodjack33
    Joined: Aug 19, 2019
    Posts: 995


    Is it 1/2 way between a rumble and knock ? Back in the late 60s/early 70s Ford produced a lot of "soft cranks" that were famous for their bottom-end rumble. I had one of these "rumblers" (302ci) in my '40 Ford pickup...ran great, 60lb oil...just learned to live with it, put 35k miles on it in the truck.
    Also, remember these engines are externally balanced, A mis-match balancer and flywheel/flex plate will make it much MORE noticeable.
    loudbang likes this.
  11. Italianjbond
    Joined: Mar 2, 2020
    Posts: 7


    I bought a new flywheel for it and the front balancer is the correct one.

    Sent from my iPhone using The H.A.M.B. mobile app
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  12. Mimilan
    Joined: Jun 13, 2019
    Posts: 569


    The balancer
  13. That’s not gonna help
    sunbeam, VANDENPLAS and loudbang like this.
  14. sliceddeuce
    Joined: Aug 15, 2017
    Posts: 2,982


    It will too.
  15. Italianjbond
    Joined: Mar 2, 2020
    Posts: 7


    This wouldn’t help.
  16. does it make the noise with the belts removed?
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  17. Italianjbond
    Joined: Mar 2, 2020
    Posts: 7


  18. foolthrottle
    Joined: Oct 14, 2005
    Posts: 1,033


    Thrust bearing? loose torque converter bolt? cracked flexplate
    loudbang likes this.
  19. Toqwik
    Joined: Feb 1, 2003
    Posts: 1,306


    My first thought would be to check the oil pan isn’t dented from hauling, storage, whatever. I wouldn’t rip it apart and throw rings and bearings at it, they might be perfectly fine. You need to try to pinpoint what area of the motor it is and go from there.

    Sent from my iPhone using H.A.M.B.
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  20. Marty Strode
    Joined: Apr 28, 2011
    Posts: 4,871

    Marty Strode

    I would pull the pan and look at the bearings, one by one. For the cost of a pan gasket, you could thoroughly clean the pan, and eliminate that suspicion.
    loudbang and Bandit Billy like this.
  21. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 6,551

    Bandit Billy

    One of my Bandit TAs had a similar issue a few years back. Ran great, sounded great...until I bolted up the exhaust. Once it was quieted down I could make the mains talk with a little rev. I knew I had a rebuild on my hands and the sooner the better.

    We don't always want to hear what they are telling us, but they are talking all the same.
    Desoto291Hemi and loudbang like this.
  22. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,022

    427 sleeper

    Guess that rules out the waterpump...
    VANDENPLAS and loudbang like this.
  23. partsdawg
    Joined: Feb 12, 2006
    Posts: 2,668

    from Minnesota

    Change oil and inspect the drain pan.
  24. junkers72
    Joined: Sep 21, 2014
    Posts: 44


    Get that fuel pump off of there and block off the hole temporarily. It’s the easiest thing to rule out before “digging in deeper”

    Sent from my iPhone using H.A.M.B.
  25. Does the knock get louder when you blip the throttle? Or can you put it under load in gear and give some throttle?
    My experience is a rod knock will get louder under some load, either revving up or against the trans. It will quiet momentarily when you let off from higher rpms. Unless the bearing is really bad.
    You can also carefully open the oil filter and look for metallic shiny bearing material.

    Sent from dumb operator on a smart phone
    VANDENPLAS likes this.
  26. Doublepumper
    Joined: Jun 26, 2016
    Posts: 609


    Hard to tell from my chair......might check for timing chain slop is the only thing I can add.
  27. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,120

    from Brooks Ky

    Obviously you want to try the simple things first.
    So far I think the suggestion by Vandenplas is the best starting point. Get a stethoscope and when the noise starts, go over the engine and maybe the bellhousing and you should be able to at least get close to the origin of the noise.
    Since you have good oil pressure, I would consider opening the engine is probably not necessary.
    You might have some piston slap or rocker arm problems. If you have a rod problem it should be easy to find with the stethoscope.;)
  28. See ! What did I tell you ?
    VANDENPLAS and Desoto291Hemi like this.
  29. slowmotion
    Joined: Nov 21, 2011
    Posts: 3,192


    I'd investigate the fuel pump, then torque converter bolts, before I started tearing it apart.
    Had an OT once that I woulda swore was history. Loose T/C bolts...

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