I'm gonna prognosticate that the "Sound" (Un-Bearably High Pitched Screeching)
(Metallic) you're hearing is a Spun Bearing...Um, Rod type most likely.Look very
closely at the Two drive chains (Timing/Camshaft and Oil Pump) and their sprockets.

If it's "Spun One" there'll be metal fragments everywhere.You must make sure
that all the fragments are GONE.Do not forget the Oil Cooler,it's on the Pre-Filter side of the Lubrication circuit.

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'84 300SD sold
124.128