Hi There!!

I have a 1986 slant six motor that raps and knocks when I first start it up (this has just begun happening). It last for two seconds or so before it clears up. I am using Rotella Synthetic 5W-40W oil. I've tried changing the oil filter twice using Purolator Brand and even trying K&N brand filters with same results. When driving it on the highway, it doesn't sound bad..only at start up and my oil pressure registers at 40 psi and drops to around 20 psi when hot on the factory electric gauge in my 1973 Power Wagon. It does have the stock oil pump so you know.

Any info or suggestions are greatly appreciated! Thanks for taking the time to read this and help me keep my sanity!!

Have a GREAT Day!

Kevin

Sorry to say this, but this sounds just like mine a few months ago.
It was ALL bearings!
I got new ones, but I had to redo everything last weekend, and found a leak in the oil pickup...
Even the cam looked real ugly!(the fuelpump-lobe is gone)
I dont say yours is as bad, but be prepared.
Your 86 has hydraulic lifters, so I guess they could make some noise?

Good luck anyway!