Been looking all over on the web for info! I had my motor rebuilt about a year ago and ever since it has a clattering startup. It doesn’t happen every time but most times. The second the oil pressure switch makes and my oil gage
goes to its dummy spot the clatter stops. It only ever last a second but it is pretty loud. Running motor craft filter. I have tried 5-40,5-20,5-30. Nothing makes a difference I am trying to figure this out. Any info would be appreciated

 

Welcome to the forum

Reads like a bad lifter spring, they hold a lifter tight until oil pressure can take over

For now you can use Clear Flooded Engine routine to stop the noise, and high wear, at start up

All fuel injection computers have this routine to Clear a Flooded Engine
Turn key on
Press gas pedal down to the floor all the way and hold it down<< at 0 RPMs and gas pedal sensor at WOT(wide open), computer will shut off fuel injectors, to "Clear a Flooded Engine"

Now turn the key to START
Engine should just crank, should NOT fire or start, has no fuel
But it does pump oil up to lifters and all bearings

After engine cranks for say 5 seconds, release the gas pedal and injectors will start and so will engine and noise should be gone

I use this every morning on my high mile 4.0l engine, prevents oil dry starts, if it sits for more than 6 hours or so the oil drains down because of the larger bearing gaps on the high mile engine

If your engine starts with gas pedal to the floor, then you don't have full throttle any more, but there is a easy fix
You throttle cable has stretched after 26 years
Google: Ranger throttle cable mod

Clear Flooded Engine routine is also good for a few other tests, like leaking injectors

 

I have a 96 ranger with a 2.3 that has recently started to do the same thing, however, it has over 250,000 miles on it, so in my case it must be due to bearing wear. This should not be the case with your engine unless the bearings were not matched properly to crankshaft when the shaft was machined, as most are during rebuild. I am going to see if RonD 's suggestion works, if so, it could be your cure as well.