305 heads on a 350 need help!

[MagicRat]

Did you put in a new oil pump when you put this thing together?

Pumps wear out, in that the clearances between the two pump gears and the housing gets too big.
When this happens you get low pressure as you describe.
If the pump is new, the pick up tube may be leaking or the pressure relief valve is stuck open.

BTW the low pressure might have wiped your bearings. If you drop the pan to change the pump, take off a couple of bearing caps and have a quick look at the bearings for signs of damage.

[bobss396]

Good idea to park it for now. You should have good oil pressure at idle, I'd like to see 30-40 lbs myself. My big block had 60 at cruising speed with straight 50 weight oil.

Did you change the cam bearings? The oil holes have to line up with the corresponding holes in the block. Since you have a knock already, as someone else suggested, drop the pan and look at some of the main bearings. If you could isolate the knock to a particular cylinder, pop off the rod caps on that journal.

I think that your oil pump is the root of all your problems. The pickup tube might be loose at the pump casting. I never play with used oil pumps, they are cheap enough for a name brand one. I like to use a high volume one as opposed to a high pressure one. If the tube feels loose (yours may have fallen off) I stake it in place with a sharp punch. Pull the pump cover and look for metal shavings or heat discoloration, in any event, chuck that oil pump.

I hate to say it, but you're probably better off pulling the engine and putting it on an engine stand. Do you know how to use Plastigage for checking bearing clearances? Most good parts stores carry them and they do come with instructions, or you can ask here. Also take off your oil filter and hold it in a bench vise, cut the can off towards the base with a hacksaw. Look at the element closely, take it apart if you have to. If you see any appreciable amount of metal (more than a speck or 2), I would take the entire engine apart for a good inspection followed by a professional hot tanking.

Bob

[roy r]

please keep us posted stewertbc
i'm dying hear how this all plays out

[superchuckles]

there is the possibility that your oil pump pickup is either coming off or developing a leak - or getting plugged up even. possibly your spin on adapter has a malfunctioning bypass valve & your filter is clogged? the only other thing i'd think would be a bearing going bad (rod bearing would not only explain the lower end knock, but also the oil pressure loss as well). best to be safe than sorry - yank the motor, pull the oil pan, check your bearing clearances. i know it's a pain in the butt, but - better to buy a new pan gasket & spend a few hours pulling the motor than to throw a rod & have to buy a new motor altogether. get yourself a plastigauge & check your clearances. there's really not a lot to go wrong in your oil pump, but - i trust you DID replace it when you did the bottom end, right? (i mean, come on, you're going to do all that & not put in a new oil pump? that would be like buying a new car but putting in your old oil filter or spark plugs only worse! the oil pump is the life pump of your engine)