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Knocking noise; seems different from others

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moroza
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Knocking noise; seems different from others

Post #1 by moroza » Sun Feb 17, 2019 10:17 pm

My 300 six is running pretty well since new lifters. Oilpressure has gone up too, though I'm also running heavier oil than before (Shell Rotella 15W40) - at least 19psi hot idle, 25-40 driving around. However, there's a knocking sound that doesn't quite match any I've read about. It's a medium-light knock like a diesel, only happens under light load - but not no load - and medium or higher RPM. With no (external) load or high load, or at idle, it's absent, which makes the pull-plug-wires-til-it's-isolated test impossible (I suppose I *could* drive it a few times on five cylinders, but I'm concerned about gas washing the rings). It may be absent when cold, but certainly more present when warmed up.

Furthermore, there's another knock that may or may not be the same. That one is occasional or very intermittent, does happen at idle, and seems to go away with the clutch in. It also is quieter or absent when cold.

Main bearings are louder and deeper. Connecting rods seem to be worst at startup. Wrist pins are reported as being present at idle. I'm stumped...

Max_Effort
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Re: Knocking noise; seems different from others

Post #2 by Max_Effort » Mon Feb 18, 2019 5:25 am

Does the knock happen when you accelerate, coming in around the shift points? Then go away when you let off? If so, I'd suspect broken piston skirts.

Note: I'm assuming you know what spark knock (detonation) sounds like. If not, take some timing out and test drive it.

sdiesel
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Re: Knocking noise; seems different from others

Post #3 by sdiesel » Sun Feb 24, 2019 1:03 am

Try a different oil.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

Fordman75
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Re: Knocking noise; seems different from others

Post #4 by Fordman75 » Sun Feb 24, 2019 1:35 am

I've also seen the oil pump pick up tubes with cracked/broken support brackets. They would shake and hit the oil pan causing a knocking sound. I got a couple good engines very cheap because of that! :D
Ted

54 Ford F100/F150 4x4
300, NP435 4spd, NP205 transfercase

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JackFish
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Re: Knocking noise; seems different from others

Post #5 by JackFish » Sun Feb 24, 2019 10:39 am

Fordman75 wrote:I've also seen the oil pump pick up tubes with cracked/broken support brackets. They would shake and hit the oil pan causing a knocking sound. I got a couple good engines very cheap because of that! :D


Had that happen on my 200.
1978 Ford Fairmont station wagon
1978 Ford Fairmont station wagon
Yup, I bought another one.
1996 Chevy Caprice 9C1 (3)
1999 Dodge Ram 2500

Kyap88
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Re: Knocking noise; seems different from others

Post #6 by Kyap88 » Tue Mar 26, 2019 2:44 pm

Did you ever figure out what it was for sure making the knocking noise? My truck is doing the same thing. :bang:

moroza
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Re: Knocking noise; seems different from others

Post #7 by moroza » Thu Jul 11, 2019 1:17 am

I only tested it briefly, but it appears that most of the noise is the vacuum advance. I connected the hose from the distributor to a vacuum gauge, which read zero with closed throttle, quick jump at the slightest throttle angle, decrease with further throttle angle, and increase with RPM - the same conditions as the noise, which was now mostly but not entirely gone. I reckon what's left is various powertrain slops during load transitions.

moroza
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Re: Knocking noise; seems different from others

Post #8 by moroza » Tue Jul 16, 2019 3:40 am

Tested further with different ignition timing settings. Now my ears have trained to two distinct noises: 1. a diesel-like higher-pitched rattle that went away after I retarded base timing a hair, and 2. a lower-pitched mechanical rattle from engine or trans internals, or possibly the clutch. The tricky bit is that the noises happen almost exactly under the same conditions. Still looking for the source of noise #2, though it isn't severe and the engine sounds and feels healthy otherwise.

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GPGoverMPG
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Re: Knocking noise; seems different from others

Post #9 by GPGoverMPG » Tue Jul 16, 2019 7:39 am

My story. My truck had an odd rattle sound driving at around 50mph or so. It was the light throttle changes to maintain speed that caused it to get loader or more noticeable. I played with ignition timing and fuel mixture and it would change but was still there to some extent. I ended up pulling the oil pan and checking the rod bearings by rotating the crank back and forth a few degrees and watching the rods where they attach to the crank. There was some tiny movement of the crank before the rods would start to move. I changed the rod bearings and the noise when away. Truck has been running great ever since. My only regret is that I did not change the main bearings also. I'm building a replacement motor so this was just a keep it running until I swap engines deal. I sure replacement of the rod and main bearings would have been a long lasting fix. Good luck
71 F350 4x4 Super Duty 7.3 IDI
72 F250 4x4 4speed 300 I6
72 F100 2x 428 Tri Power
2014 SHO

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Grahamexl
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Re: Knocking noise; seems different from others

Post #10 by Grahamexl » Sun Sep 15, 2019 4:48 am

Hello guys,

There can be various reasons for rattling and knocking noise: a plastic wheel-well protector may come loose or some plastic under-engine windscreen; brakes missing shims; a pebble rattling around trapped in the brakes or wheel, etc. A friend of mine had similar issues with his 2009 Pontiac Vibe GT.

Harte3
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Re: Knocking noise; seems different from others

Post #11 by Harte3 » Sun Sep 15, 2019 11:03 am

Ghost and intermittent noises are difficult to isolate. It is impossible to do so over the internet.
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

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Grahamexl
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Re: Knocking noise; seems different from others

Post #12 by Grahamexl » Sun Sep 15, 2019 1:30 pm

Grahamexl wrote:Hello guys,

There can be various reasons for rattling and knocking noise: a plastic wheel-well protector may come loose or some plastic under-engine windscreen; brakes missing shims; a pebble rattling around trapped in the brakes or wheel, etc. A friend of mine had similar issues with his 2009 Pontiac Vibe GT.



It had a specific rattling noise coming from the right front quadrant - it was audible when driving at highway speeds - 70 MPH+ (when he was practicing at a driving school (Cantor's Driving School in Phoenix listed here), the instructor let me drive his own car). So he had the hub and bearing replaced - the noise is still there. Now, his Pontiac is standing in the garage, he just doesn't want to spend money for a repair service.

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