[snakeknuckles]

long story: So I have a 4bt in a pettibone forklift that I got with a blown motor- #3 rod thru block due to runaway injection pump... I found a long block on ebay for $500. It looked like it had been rebuilt but had sat outside in water and had lots of rust damage. Cam looked brand new, so did rods and crank however on close inspection, #2,3 rods had spun bearings and rods had overheated in process. Ended up using ebay block, new cast crank (china), new head (Minnesota), two rods from blown motor, two from ebay motor, , new pistons +.010 (bored), oil pump from ebay motor (because it looked brand new), rebuilt injection pump, new turbo... Machine shop cleaned, bored, decked block, setup crank, rods, pistons. I assembled the engine put it back in machine. Machine had only oil pressure light. I installed gauge as well. Motor runs perfect. I have run it 4-5 hrs. It purrs like a kitten. Oil pressure is 10 psi at idle, comes to 30-35psi at speed. I have checked oil pump, oil pressure release, oil filter, oil cooler, plug in block at push rod cover. removed timing cover to look for gusher there. ran motor with timing cover off- no gushers there. removed oil cooler to check for flow/pressure from pump- It seems like there is good pressure there as I could not hold flow back with my thumb when cranking with starter. What to do? Should I just put the thing back together and run it? (The oil pressure light goes out) Where could I be losing oil pressure? Thanks for any advice.

 

[redhedbronco]

At idle Im around 40-45psi on an old, severely flogged, hi mileage motor. Is gauge new? Mech or electrical?

 

[eggman918]

35-40 at idle and 50-55 at speed 300k mileage

 

[snakeknuckles]

Gauge is mechanical.

 

[Death Row Dave]

I would suspect bypass stuck open or stuck . 35-40 at idle and 60-65 2500 rpm

 

[snakeknuckles]

Which bypass valve? The pressure relief valve is good. The oil filter bypass is good- but even if that were stuck open, it should not cause loss of oil pressure. As best as I can tell I am dumping oil back to the oil pan on its way to the crankshaft. I think I need a good block oil schematic...

 

[oshpunit987]

Your new gauge may be bad. There are several places on the block where you can put another gauge to verify the pressure.

 

[snakeknuckles]

done that... checked gauge. Next step is to make a plate to cover oil filter inlet and tap for pressure gauge- to check pump,cooler, relief valve circuit-assembled-If I see good pressure there (cranking with starter motor then next I will attach a gear pump to oil filter outlet and pump oil thru engine to see where oil goes- I'll let you know

 

[redhedbronco]

It seems this has happened a few times in the past and sometimes the cause turned out to be an incorrect oil filter adapter gasket but it seemed they had no pressure at all IIRC. Something else, changing out some rods and a new crank. Was it all miced/plastigauged to spec? Used oil pump? Im curious as hell.

 

[snakeknuckles]

Sure enough... wrong gasket between filter and cooler

 

[redhedbronco]

Cool. Cheap fix. What #s are you seeing now?

 

[snakeknuckles]

I get 40 psi at idle and 60 wide open!

 

[snakeknuckles]

Just to clarify how this whole situation evolved:
I had two motors to pick parts from: one that had thrown rod thru block and one that I got off eBay for the block. They both had what appeared to be identical oil pumps, oil coolers and filter housings. When I assembled the rebuild I used my original oil filter and cooler. I think I left the original gasket between cooler and filter housing because it had a slot between the two oil cooler ports instead of two holes. Gasket looked perfect and had been on a motor that had 11,000 hours so I thought it should be right. Pressure relief was clean and worked well and everything else was clean. After I saw the low oil pressure condition
I made a plate with pressure gage and nut to cover where oil filter screws on to test everything before the filter. The funny part is that is that the first time I tried the test plate I got 20 psi with stater. I'm not sure how I saw that because subsequent tests showed 0. I finally took off cooler and filter housing and bolt them together on bench and pressure checked assembly with test plate installed. With air, all pressure was dumping back to block orfice! Changed to the 3 hole gasket and now gage showed pressure. It is still not clear to me where the gasket breach was but anyhow that was the problem.

Tx