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Discussion Starter #1
Hello
Recently re-built a 4b 3.9 (1989) off a Morbark chipper.
I had good oil pressure 35-45 lbs after overhaul and it runs great. Total overhaul with new pistons, bearings, etc.
I had a small water leak coming from the oil filter/cooler housing.
So, I went to Cummins and $50.00 later, came out with two new cover gaskets.
Immediately after start up i had oil pressure (cold engine). After warming and throttle up to 1500 and then at 2200 RPM (warm engine), I throttled down and the engine died as the low oil pressure gauge circuit did its job when the engine oil PSI fell below 20 psi.
I now have low oil pressure. At idle, 15-18 psi and at 1500 rpm, maybe 25-30. Very different from my readings before I changed the gaskets.
I noticed that my housing does not have a bolt in the lower tip of the cover. Meaning I have 14 bolts instead of 15.
I did not look at the old gaskets or compare. At a glance they looked identical and both sets were original cummins parts. Any help is appreciated.
Is there different covers or gasket part numbers that could block or obstruct an oil port?
 

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Was the bypass valve and regulator still in tact when you took the housing off?


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The Filter bypass and the regulator were not disassembled when I replaced the gaskets. I did push on the filter bypass with a finger and felt a slight spring tension but did not do anything else before cleaning gasket surfaces and re-installation of housings.
When I started getting lower oil pressure immediately after assembly, I removed the Regulator and the piston moved freely and easily slid out with my pinky grabbing it. I did not look down in the hole as it was full of oil and difficult to get a good look while on engine. This engine got 25 psi just motoring with the starter (no injectors) which is why i am so concerned. Now it gets 12psi after this action. I was going to bring the old gaskets over to cummins and have them pull the exact same part numbers they recently sold me when i did the gasket change.
 

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Cummins has 2 different style gaskets depending on which engine you have. Most gasket kits come with both so you have to choose the one that applies to your engine. Here are photos of the 2 different types. The first one is the style for the 4bt and 6bt. The second one is for the STORM blocks used in later engines.
 

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The Filter bypass and the regulator were not disassembled when I replaced the gaskets. I did push on the filter bypass with a finger and felt a slight spring tension but did not do anything else before cleaning gasket surfaces and re-installation of housings.
When I started getting lower oil pressure immediately after assembly, I removed the Regulator and the piston moved freely and easily slid out with my pinky grabbing it. I did not look down in the hole as it was full of oil and difficult to get a good look while on engine. This engine got 25 psi just motoring with the starter (no injectors) which is why i am so concerned. Now it gets 12psi after this action. I was going to bring the old gaskets over to cummins and have them pull the exact same part numbers they recently sold me when i did the gasket change.
Time for new ones. They should be fairly stiff. The bypass should open at 70-80 psi or when filter is clogged. You should get 25-30 psi at an idle unless you have a bad pump or bad bearings.


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The minimum allowable oil pressure at idle is 10 psi, Thats of all B series.
Thanks, Scout, that's valuable info for all of us to keep in mind!
 
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