No mention whether the engine has a recent rebuild or if had been vatted. Before pulling engine remove the oil sending unit and take a straight piece of coat hanger or welding wire and stick in the hole that the sending unit came out of.About 4 inches down in the hole 340s have a small plug about 5/16s in diameter that looks like a small freeze plug which diverts oil to the top of the engine. Sometimes when vatted this plug comes out and the result is poor oil pressure. If the wire goes 6 to 8 inches down the hole then that plug is missing. Easy to check before pulling engine and can be installed from the top.Hope this helps!

this thing at idle has 9 lbs. And holding it at about 2000 rpm it has 35 lbs and will drop slightly while it is revved up to 30 lbs. I recently pulled the distributor out and used my drill with the priming rod and it held 50 lbs. I don't get it?

you have to take into account you drill may be running faster than the distributor drive is. And no I do not know what the ratio between the crankshaft RPM and distributor drive is. only other explanation would be cold vs hot oil

I just did the wire hing and there is no plug. I took ,y light also and looked down the hole there is nothing there.

If I may respectfully disagree, if that internal plug is missing the oil psi will be the same or even a bit higher (cuz the oil has a straight shot vertical up from the #5 cap to where it turns into the horizontle gallery & it ain't held back by the filter restriction) however the oil will be unfiltered (very bad deal) & if that ain't caught early on the eng will have an earlier(er) demise years on down the line while all the time the owner is thinking he is doing the right thing/being proactive with frequent oil/filter changes. We gotta find out what passage etc (something) that is being partly uncovered etc when it is running that ain't opened when bench testing with the primer. I'm thinking it is lifter related.

well once the lifters are pumped up solid they should stay solid,am i correct? If I have some lifters that are not holding pressure then i would assume they are bad lifters.

I'm thinking the height of the side oil hole/gallery height interface especially if lifter to wall clearance is healthy. I'm just thinking out loud but we are losing alot of PSI & not thinking that the crank/bearing clearances would be altered significantly from running/not running esp if you are running full groove mains (but I ain't sure on this/just speculating) but with FG mains I'd think the passages (saddles to crank innards) would be open all the time.

Fix the broken part first and see if that is the problem or not You have treid a lot of things to fix this problem You have now found a problem that needs fixing so fix that and see what the results are

The lifter on the one we were working on did bleed down when the pressure got low, replaced it a couple times and no difference.

Cab is right, fix what you know is wrong and go from there.

FYI full groove bearings do tend to cost a few PSI.

The ratio between crank and distributor is 2 to 1 so if your drill turns 500 RPM it is like the engine turning 1000 RPM. Also the cam lube may or may ont be getting through depending on where the cam is stopped when drill priming.

Thanks guys for all your input, I almost have the engine out so im putting new bearings and oil pump also new cam and lifters ( I DID"NT LIKE THE ONE IN IT ANYWAY ) And cam bearings. I have the front off the motor and pulled the cam out, FRom my past memory one of the cam retaining bolts used to have a hole in it. This one has all solid bolts. I'll read my manual and check that out.

They only have a hole through them if you put a hole in it. I usually do it on the top passenger side bolt to drain the little puddle onto the chain, gives more chain lube and aids drainback time.

Some OE had a 1/8" hole in the top pass bolt and some had the angled drip tray & a guy said some had both. It is a drip oiling and I drilled a good sized hole in the retainer flat plate and a .015" hole behind that in the front pass mini cup plug in the front of the horizontle gallery for a constant squirt onto the chain and the same .015" hole in the rear 3/8 NPT pipe plug in the drivers rear of the horizontle oil gallery for a constant squirt onto the intergear (when you preoil you can see its function). Get an aluminum pipe plug & drill it REAL slow especially on steel ones like the cup plug & buy several of the .015" bits as you will likely break one especially on the steel front cup plug.

What would they call this plug at the parts store? I sure want to put it back in while im working on this thing.

Ma has it & a parts store would also & likely called a cup plug. its a small one & you need the exact size. You drive it in up thru the #5 main cap block saddle

So if I understand this thread correctly, this "cap" cannot be installed from the top of the engine! It must be installed from the bottom? I am having the same problem, on a 340. No one has been able to figure out why the lifters rattle.

My 340 rattled when they didn't install that plug but also missed the threaded plug in the galley by the distributor!

That normally ends up with a motor having no oil pressure, epsecially when trying to prime it with a drill motor, don't ask me how I know that now There be two galley plugs on Mopar SB motors on the drivers side at the rear of the block, the large one one is for access to the smaller one inside in front of the distributor and that one is essential to seal the oil galley passages up on that side

Ok now we are confused. 68 gts said you can put this plug in from the top. Who is correct?

installing vertical oil gallery plug. bottom saddle hole ID .570". top threaded NPT sender hole .336" (& NPT threads get narrow(er) further down).