Hi all. Not a frequent poster, but have exhausted all normal ideas on diagnosing a loud knocking sound (sounds like rod knock) in my '68 Charger, but can't find the culprit.
The engine is a flat-tappet hydraulic cammed 440, .030 over, built by Muscle Motors (now defunct) in 2014 and only has about 1000 miles on it. It runs excellent except for the knocking sounds. I've owned only Mopars & built dozens of engines in the last 35 years, so I've got a bit of experience in them, but this one has me stumped.
Upon engine startup, it immediately makes a LOUD knocking sound...almost like two solid pieces of wood are being hit together. The sound varies with engine speed...slightly quieter upon deceleration and it makes no difference hot or cold. The car hasn't been driver particularly hard, with few acceleration runs and all below 5700 rpm. I've chased about every possible culprit and googled every board for similar problems, but none of the fixes worked.
The noise can be heard most clearly at the front of the block...using a stethoscope and/or "wood block" trick and you can even feel the knocking at the front engine stamping pad...across the intake hold down, by the thermostat outlet...and less on the passenger side and even less as you go towards the back of the engine. Pulling the spark plugs one at a time makes does very little for the knocking sound, BUT when the #1 cylinder wire is pulled, when you put the plug wire back into the distributor cap, the very first spark makes the knock loud...ONCE. Just like a "pop" knocking sound, and then a continuous lower knocking sound.
Armed with that, I figured it was the rod bearing....but:
- I have good oil pressure (~60 psi cold, ~ 30 psi hot idling). Replaced the oil pump with a Melling high volume (no change in condition); Oil changed (twice) with Valvoline VR1 10/40...and a second time with VR1 20/50, but neither made a difference in sound.
- Pulled the oil pan & checked all the rod bearings. They are all in excellent condition, no noticeable wear (particularly #1) and they all measured between .0015-.0025" clearance. Nothing excessive or out of the ordinary. For good measure, I replaced all of the rod bearings while I was in there but the sound didn't change at all.
- There was no metal or foreign substances in the oil pan at all;
- Also checked the valvetrain. Nothing wrong there: all cam lobes are good, all pushrods are straight, all rocker arms, springs, valves, shafts, and assemblies are tight, not hitting, or show any signs of anything amiss.
- Someone suggested that maybe the mechanical fuel pump and/or pushrod may be worn/bent/etc. Pulled the fuel pump pushrod and it is straight & correctly lengthed...no signs of wear or tear. Checked the fuel pump arm and pump...no issues. Even ran the engine with the fuel pump removed...same knocking sound.
- Checked all belts, pulleys, and systems with nothing wrong there. I went so far as to run the engine with the alternator belt disconnected and then the power steering belt disconnected, with neither one affecting the knocking sound.
- Pulled the timing cover and checked the chain & gears, but all was good with no signs of damage, wear, or other obvious concerns.
- All valve covers, oil pans, and other areas were pulled to see if there was anything hitting, with nothing showing.
- All exhaust gaskets & fittings were checked & or/replaced, but none of this affected the knocking sound.
I'm at my wit's end. The sound is LOUD and definitely near the front of the engine, but seems like #1 rod bearing...but that checks out. Could #1 piston be so loose in the bore that the piston slap sounds like a bad rod? The noise has not always been there, and the car was in climate controlledstorage for 2 years (2018-2020), but everything was checked out prior to start up then.
Help!
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