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Replaced water pump and harmonic balancer, fixed oil pump bracket in oil pan, checked 1, 2 and 4 main bearings (some unusual wear, but nothing out of spec. limits), check 1 and 2 rod bearings (again, some wear but nothing out of spec. limits).
Still have the same sound/issue.
Any thoughts on culprit/repair? It's driving me nuts and I want my truck back!
I would pull all of the belts. Then run it BRIEFLY (obviously without the belts your water pump won't be running). If the hum/whine is still there, it is likely an internal engine noise. If the noise goes away, try putting back on belt at a time. You've replaced the water pump, so put back the water pump/ alternator belt. If the noise is back, it is probably the alternator. If you have power steering, a likely suspect would be the power steering pump. That is not to say that it is necessarily bad. They are notorious for being noisy. I replaced mine because it was loud. The new one sounded exactly the same.
Short bed pickups are like ***** on your ex-wife: if they are dressed up they may LOOK nice, but that's all they are good for!
If you want a TRUCK, buy a long bed. If you want a GROCERY GETTER, buy a Taurus. Short beds are just rolling parts donors.
Would this be a possible culprit of a dull "knock" coming from the bottom of the block (when listening with a stethoscope)? There is also universal wear on one side of the cap. This is #5, which also serves as a thrust bearing (I believe).
If you listen at the sound, you can almost tell when the piston hits the top of the stroke (higher pitched thud) and the bottom of the stroke (deeper thud). It's also got the constant "1 2 1 2 1 2 1 2" rhythm of something like that.
That's not the cam walking, it's not the timing gears (you can hear them humming in time with the engines RPM), it's not valve-train noise, so...
That leaves drive-train noise.
You said you check the main bearings on 1 2 and 4, so maybe it has loose wrist-pins?
It's definitely a bottom end noise, as far as I can tell.
You sound like you know what you're looking at. Do you know the history of the motor? How well has it been taken care of? Was it horsed around, or have high mileage, etc.?
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