HD5 with 2-71 Oil Pressure Problem

2-71 don't have great oil pressure to start with but the main source of low pressure is rod and main bearing leakage . 
 The oil system is a bypass system with just a small amount of oil diverted to filter , evidently your orifice in that line is plugged - it should be about 1/8" hole in fitting and line to filter . Cam bearing wear also leads to low pressure . 
 When I bought my machine owner told me they had put bearings in it but thin oil for winter use was why pressure was low , changing oil didn't bring pressure up nor did replacing the oil pump with a new one . Later I developed a oil leak at rear main and found they put rod bearings in but not mains and crank was worn enough at center main it moved enough to take out rear seal , Had crank turned , new rod and mains and replace thrust shields , new rear seal of modern type , replace flywheel bearing with sealed bearing and remove wick in end of crank for old bearing oiler , 
 Pressure came up but still seems lower than I would like to see - Only have 25 years of running since so it might be OK . 
 I did put a oil pressure switch into system so I can tell when running at a angle or up or down hill if oil pump is starving - big red light on dash comes on so you can correct situation before damage 

All the diesels of that vintage seem to make the oil black in just a little run time. And DD even faster.

Thanks for all the info. I did a complete oil change and ran it for a bit. When I checked the fresh oil it looked like it had metal in it. Looks like time for a rebuild.

I finally got a chance to dig into the old 2-71. It looks like the former owner did some interesting repairs. This guy was very fond of orange silicone. I pulled the water pump and oil cooler housing and found gobs of of the stuff clogging almost every oil passage in the top end. He also did some kind of bypass on the oiling system for the top end. Any idea why he would have done this? Seems like this would limit the amount of lubrication getting to the top end?

Sheet gasket material even old paper grocery bags were good for replacement hand cut gaskets in a pinch with a LIGHT coat of HiTack or Indian head style sealers.

I've solved a problem with low oil pressure on a 2-71 I rebuilt!  I had tried just about everything, pump clearance, reduced main and rod bearing clearance, shimmed pump regulator - nothing worked!  At best 25 psi fully warm with SAE 40 oil.  Then recently I got looking at the cam bearings that had been replaced when I had the block tanked at a NAPA machine shop.  To my shock, the bearing that had come out were marked 0.030 inch undersized!  I had unknowingly put in standard bearings with an undersized cam and balance shaft.  So, instead of having about 0.004 inch clearance for the 5 cam and balance shaft bearings, each had about 0.034 inch clearance.  When I looked at a Detroit Diesel parts book, I found they sold bearings and that were 3 sizes: Standard, 0.015 and 0.030, with the  undersizes apparently for reground cams!  I had another set of parts in my shop and found another one that used 0.015 bearings.  I have heard of cams that had profiles reground, but in all my years working on engines had never run across undersized cam bearings.  After over 2 years, I pulled the engine and installed a set of 0.030 undersized bearings from Detroit Diesel and I now have excellent pressure.  Full story of myFaramall 400  repower with the 2-71 is on my website;  https://dieselbobllc.com/farmall-400-2-71-repower-project/, I'll eventually add more detail and part number there.

I read this whole thread, and I am jealous that you can still buy parts for these machines, but I have to wait 6 months to buy a new clutch disc for my HD6G. Anyways, glad you solved your problem, and once again, never throw the old parts away..........

Coke-in-MN wrote: Detroit had enough of a market for all there engines that parts were out on the market for years , nice thinng is 2-71 pistons are the same as 6-71 pistons . Sleves interchange also -

  Same with the AD4 Perkins in my MF65. Bought brand new crank, rods, gaskets, etc.