hey Ive got a 97F150 4.2 5speed with 119 on it. bought it at 100k last year and parked it till i could change the gaskets (so it wouldnt hydrolock). . changed em about 4k ago. my buddy and I did it. here's how: we left the engine in the truck. pulled everything down to the heads. cylinder walls looked great, rollers, etc. had one warped valve (replaced.) replaced head gaskets, plenum gasket, intake manifold, etc. he determined it didnt need rings... we put oil on top of the pistons, two days later it all was still there. so he said we didnt need to tear it down any farther. I thought my oil consumption would slow. but it hasnt. it doesnt use any coolant now, and runs so much smoother. but i am still pouring oil in it every other day. and the oil gets dirty really really quickly! in a thousand miles, it needs to be changed. and a couple times, when sitting at an idle, oil pressure has dropped to zero, then come back up. It also fouls two spark plugs fairly often. I can hear some knocking. he says i have loose bearings in the bottom. IDK as this is my first engine build. I used felpro gaskets, and always use good oil with a motorcraft filter. any advice guys????

 

Felpro gaskets? those are the incorrect ones! they are the ones that caused the hydrolock!

if that doesnt solve the problem sounds like bad piston rings

 

The oil pressure dropping to zero and coming back up is most likely the sending unit. I would replace it if it continues. How much sludge was in the engine? May need to drop the oil pan and clean the pump strainer if the pressure is indeed dropping.
But, it sounds as if you need to rebuild the short block

 

Did you just replace the one valve? or was a complete valve job done?

Have a leak-down test (not a compression test) done, it will tell you if it's the rings or valves...

 

we replaced one valve. the rest were cleaned with this special stuff. i dont remember what it was. but they all seemed to seat fine. as far as the sending unit, when the OP dropped, so did the tach and the truck bogged. so im guessing the sender is fine. i found someone that said he wood put bearings in the bottom for 300 bucks plus parts. not sure what all is included in the short block rebuild. i do know that this is a pain in the asscrapper and maybe i should look for another truck, cut my losses with the money ive poured in this bitch. but i hate those fat payments.....