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Thread: intermittent knock, Please help!

  1. #1
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    intermittent knock, Please help!

    My 1964 CJ5 f-134 has an Intermittent knock, link to video below. I've dropped the oil pan, everything is tight and snug. No metal shavings in the pan, cylinder walls look great. I open the top and side valve cover and again everything look and feels what I would imagine is good. I have reach the limit of my knowledge and hope someone can help me diagnose were the knock is coming from. Anything helps, thanks.

    https://www.youtube.com/watch?v=l0H_zQnH8OE

  2. #2
    Senior Member TJones's Avatar
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    Does it knock all the time or just when you fire it up cold?
    Sounds like a loose plug blowing compression until it warms up or a leaky exhaust gasket blowing exhaust until it warms up.

  3. #3
    Super Moderator bmorgil's Avatar
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    That sounds like you may have a load of carbon or water in the cylinder. The sound of it seems like one or two cylinders. What is the condition of the engine? A lot of hours? Does it burn any oil? Has it or does it run with the choke on a lot? Is it steaming at all out the exhaust? That is a loud knock indeed!

  4. #4
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    Thanks for the replies, It'll knock both hot and cold, that video was literally the first 30 seconds its ran since late November. It has a lot of hours on it but the motor is in good shape. As for the oil it's hard to tell, I get do get some blue smoke so I'm sure i does burn a little. Thought that was more likely to be because of fuel/air mixture. The knocking started last October, it knocks while at idle and under power. After I took the video yesterday it idled for about five minutes without knocking. I shut it off added oil, changed my clothes started it back up and the knock returned and hasn't gone away. I checked the spark plugs, they're snug. Perhaps the crush rings are bad? Again thank you.
    Last edited by monty509; 04-15-2020 at 06:36 PM.

  5. #5
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    Well, that's a heck of a knock, but sound good when it isn't knocking. In my experience, a rod knock doesn't go away. You might get a wooden dowel a couple of feet long and place it in different spots on the engine and hold it against your ear and see if you can locate the area it is in. I had a Ford pickup once that developed a slight knock and could never find where it came from. Changed lifters, fuel pump, didn't help. Maybe look at the fuel pump arm.

  6. #6
    Super Moderator gmwillys's Avatar
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    Sounds almost like a wrist pin. The F134 doesn't like a lot of sustained high RPM. This will cause your intermittent knock either under load but more so at idle. With the low gear ratio, and highway speeds above 50 MPH, the engine will overspeed.

  7. #7
    Super Moderator bmorgil's Avatar
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    I was thinking maybe a wrist pin also gm. I just can't see it coming and going like that. I think you may have something with the RPM gm. monty509, does it always go away at higher RPM? If it is a wrist pin, I would assume it has damaged the cylinder wall by now. Compression in that cylinder would be low. The wrist pin is clamped in pretty securely with a bolt through the rod. It certainly could come loose. I wouldn't expect it to last long. It is so loud. I wouldn't run it like that. I think a compression check is in order. If a cylinder is damaged that should show, or if a cylinder has a carbon load compression will be high.

  8. #8
    Senior Member TJones's Avatar
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    If you watch the video close and about the 2-3 second mark, what is the spark on #4 cylinder right where the plug seats to the head????

    Could it be a dead cylinder until it fires to the electrode on the plug instead of shorting out to the block causing a dead cylinder????
    Last edited by TJones; 04-16-2020 at 06:44 AM.

  9. #9
    Super Moderator bmorgil's Avatar
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    TJ what an eye! I went back and looked and thought the same thing, it looks like an arc on number one. Closer inspection and I think it's a piece of paper or tape flipping around.

    okiemark's suggestion (fuel pump) is also a very good thought. It sounds like it is timed with the cam. It could also be a sticking intake valve or a broken valve spring, letting the valve contact the piston. That would likely bend the valve and compression should be low on that cylinder.
    Last edited by bmorgil; 04-16-2020 at 07:55 AM.

  10. #10
    Super Moderator gmwillys's Avatar
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    From past experience, the wrist pin doesn't migrate out of the piston, so the cylinder wall is usually fine. The bearing on the rod becomes oblong, and in worst situations, the rod becomes oblong. We had a Dodge M-37 with the 236 flat head. It only had 10,000 miles on the clock after a 1976 overhaul in Denver, (great thing about overhauled military vehicles is that the depot affixes a plate to the exterior of the block giving bearing measurements of either standard or oversized- and how much) The truck was used as a brush fire truck for the local volunteer fire brigade, and had a 500 gallon tank and pump installed. The 500 gallon was cut in half when the extra weight made the truck unstable in cross country travel. Long story short, being that the truck was used for travel faster then designed, the engine developed a knock. It wouldn't do it all the time, but mainly at idle. When under a load it would quite down until you decelerated, then you could hear it.

    With all that being said, it would be a good plan to check the valve train for a weak or broken spring. I highly doubt that it is on the intake side, because it is not backfiring through the carb. The exhaust valves coming up through the block will not cause extensive damage like an intake would. Since the Jeep last ran in November, it could be a possible hung valve. Then it would be as simple as working the valve to loosen it up. In your dry climate, that isn't a big probability, but worth a look.

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