M37 251 Oil pressure issues.

[ecpiano]

Chrysler flathead guys…I need some help. Here in the story for reference. 
Swapping a 251 into my M37. I found a bad main bearing and was able to source new bearings of the same size. Crank was in good shape and measurements were good. Put in new main bearings and reassembled. I needed a military oil pump as I am running military distributor. I primed the pump out of the engine and put it back in. I then reassembled the whole engine and cranked the engine with no power to the distributor and got oil pressure to my mechanical gauge. I then added power to the distributor and the engine fired right up. No oil pressure. I then removed the supply line to my remote oil filter (I have a full flow filter) and cranked with no power and oil flowed out. I put oil filter back on, cranked the engine with no power and got 20 pounds of pressure by cranking for a few seconds. I then started the engine and you can see the oil in pressure gauge line and the oil sucks back into the engine and no oil pressure.
 

I put new gauge on same as above. I took the oil filter off the filter housing and started engine. Oil came out of both holes. 
maybe my engine is missing a plug in the oil galley??

Anybody have any thoughts.

[Robert Harrison]

I think there are more questions that need to be answered in order for anyone to help you.  Can you supply more pictures of the filtration system you have installed?  Where is your gauge hooked up?  Questions that come to mind are is this the right filtration system for your application?  Is your filter plumbed back wards?  There are check valves in modern systems to prevent the oil from draining back into sump when the engine shuts down.  Take more  pictures of what you have.  Draw a diagram of the system as you have it hooked up including gauge hook up location.  The original system I am familiar with was a gravity system the oil comes in the top of the filter and essentially funnels back into the block.   More inclusive pics please? 

[ecpiano]

Top pic is the original filter system. The second is where I have the gauge, pulling from where the No.2 main is. I’ll get pictures of how I have the filter now. But all it is, is a spin on filter, I’m running the line to the filter from the top hole and the return to the bottom hole where to original filter mounted. 

[Merle Coggins]

Having oil pressure at cranking RPM but none at idle RPM makes me wonder if there is a restriction in the pickup tube causing the pump to cavitate at higher RPM. 

[tanda62]

This diagram and explanation might help.  I also wonder about the use of a full flow filter, I know on my 53 218 it uses a by pass filter so when I upgraded to a spin on filter I use a Wix 51050.

 

[Merle Coggins]

tanda62's post is in regards to the bypass filter setup. ecpiano has a full flow filter converted to use an external, aftermarket, filter so it doesn't apply in this instance. 

 

Another thought on this... If the remote filter was plumbed backwards could it be blocking oil when the flow increases? I believe the block is setup that the lower port would be flow from the pump, which should go to the filter inlet, and the upper port would then feed the engine oil galley. 

[kencombs]

Sure sounds to me as if the oil pressure relief valve has a malfunction.   Closed when cranking but when a large volume of oil flow is present it opens and dumps all the flow into the pan.   I've never worked on a factory full flow flathead, but is it possible that the valve has been exchanged with another, for a bypass system?