Rebuilt 318 engine knock

Engines, Exhaust and Fuel Systems

  1. Alexgalayda

    Alexgalayda Active Member

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    HELP I just rebuilt my 318 motor new bearings gaskets lifter oil pump and after about a month it’s knocking inconsistently I don’t know if it can be rod knock I’ve replaced the flexplate due to the old one cracking and all tourqe converter bolts are tight I only tightened flexplate to crank to where it started to move the motor no matter how hard I beat on it tho the noise does it change I’m running 20w50 with a bottle of Lucas oil pressure cold is 60 psi and warm is around 15 20 sometimes 10 if someone can help that would be great thanks
     
  2. AJ/FormS

    AJ/FormS Well-Known Member

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    Your oil-pressure numbers are fine for a stock, near-stock build.
    A rod knock is very unique; at idle is a deep,booming,not-very loud, and from the top is usually hard to tell where it's coming from. I have never experienced an intermittent Rod knock, not saying it can't happen. As the rpm goes up, the knock becomes more frequent, and usually louder.
    Isolate which cylinder it is coming from by, one-by-one removing the plug wires. When the noise goes away, badaboom you found the cylinder. If it doesn't go away, then look elsewhere.
    From the bottom, a stethoscope will tell you right away that the noise is in the bottom end, and time to drop the pan.Once the cylinder is isolated ,finding the bad bearing will be easy.

    There is no other noise that an engine can make, that sounds like a rod-knock. It sounds somewhat like a muffled hammer thudding on the crank.... which of course is what it is,lol. After the bearing pounds out, the noise changes, and then you are replacing the rod and possibly the crank too.
    If your noise turns out to be a rod bearing, you still have to figure out why it happened and fix it so it doesn't just happen again.
    If the knock happens to be #1 or #3; one of the front two on the drivers side, then that can happen if you over-rev it without having done the oiling mods, or just plain ran it low on oil,accompanied by high revs. If one is gone, you have to check the other one as well.
     
    Last edited: Aug 25, 2019
  3. XfbodyX

    XfbodyX Well-Known Member

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    Why are you running 20-50 on a motor with fresh bearings? 10 psi warm with 20-50? Rebuilt is a strong term for what you did, more like you borrowed some time.

    Id either run it and see what happens or buy another gasket kit and pull it apart but by the sound of it with as little as 10 psi with 20-50....meh.

    You didnt say what year 318 but the mid 70-s and 80-s were never meant to be ran too hard rpm wise and the internal parts and lock of balance and good factory machining shows it, look at an oem rod and cap and see all the flash from castings and the rough machine work. Ever notice how some of the holes for the main cap bolts in the block are blackish from heat of a dry bit being rammed quickly before the tap?

    You know for $700 you can buy a reman 318 shortblock and for $1100 a reman long block.



    There is no other noise that an engine can make, that sounds like a rod-knock.

    AJ I used to think that myself, ever since my youth untill I did a re ring in my early 20s and recall being pretty rough getting the pistons back in.

    A cracked skirt can and will sound just like a knocking rod with it hammering around with each stroke. I had a feeling it was a bad skirt but had countless others tell me I had a rod issue.

    I beat that motor for 60k miles and only one of the tree nights Ive ever drank killed it off, running 5500 in low all night just having fun made it knock harder and smoke. Took the head and pan off and replaced piston and things were great.
     
  4. AJ/FormS

    AJ/FormS Well-Known Member

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    I stand corrected.
     
  5. Alexgalayda

    Alexgalayda Active Member

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    I ran 20 50 to see if the knock went away but to no svail no change only time it got more apparent is when I advanced the timing
     
  6. Oldiron440

    Oldiron440 Well-Known Member

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    Didn't this thing have a knock the first time it was torn down?
     
  7. Alexgalayda

    Alexgalayda Active Member

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    Yes but that was the old block that one cracked I got a replacement
     
  8. Alexgalayda

    Alexgalayda Active Member

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    That was the old block it was cracked I did replace it
     
  9. Alexgalayda

    Alexgalayda Active Member

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    Cylinder 2 and 1 makes the most difference in sound
     
  10. XfbodyX

    XfbodyX Well-Known Member

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    Have you cut your filter open to look for metal?

    If you can drain your oil in a clean clean pan and after its drained dump a half qt of new to flush out the bottom of the pan then let that whole pan sit overnight and slowly pour it out in the sunlight and look for metal in the bottom as you get close to the bottom.

    Can make a vid of this knocking?.
     
  11. Alexgalayda

    Alexgalayda Active Member

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    Yes I’ll post a video now
     
  12. Alexgalayda

    Alexgalayda Active Member

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  13. XfbodyX

    XfbodyX Well-Known Member

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    Listen to the end of this vid of yours. Starting at say 1:25

    Does that car have a constant miss to it?

     
  14. Alexgalayda

    Alexgalayda Active Member

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    No
    No it’s randomly happens but very uncommon for it to misfire
     
  15. AJ/FormS

    AJ/FormS Well-Known Member

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    Turning on the A/C there pretty much seals the deal for rod knock.
    Now pull the #1 plug wire off and repeat and or #2
     
  16. XfbodyX

    XfbodyX Well-Known Member

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    Yep, id bet if you drained the oil and put a socket on the crank bolt and moved it back and fourth you would feel it and probably hear it.