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73 MG oil pressure decreases

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scubabatdan

scubabatdan

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Ok it has been a long 1 1/2 years of work, but I finally made my maden voyage today. Everything went smooth 12 miles to work, temp was 65 degrees. I did some in and about driving during the day. Unfortantly everywhere I parked I leaked oil, even though I installed the rear main seal conversion kit on the 1275 (Different subject) On my way home it was 90 degrees beautiful drive. Halfway home I noticed the oil pressure was 25 psi, I decided to keep an eye on it and 2 miles from the house it had dropped to 20psi. I pulled into the gas station and bought a quart of oil thinking It was low on oil. Well it wasnt. I waited 20 min and decided to get her home. When I hit the highway she was still at 20 PSI and the water temp was a tad above N, When I pulled in the drive, and let her idle the PSI went almost to 0.

I waited 2 hours and hang tested another oil gage, it jumped to 40 psi at idle 900rpm. And 50 at 3k. I reconnected the old oil gauge and got the same.
Ok Dumb founded.

The oil leak was worse until I capped the valve cover line and intalled a PCV valve from the intake manifold direct to the oil breather, but it is still leaking. Even with the new rear main seal kit.

Ideas anyone?
Dan
 
Maybe your relief valve stuck open? What wieght oil are you running? Oil pressure relief on filter housing stuck open? Doesnt sound like engine damage but could be some swarf got cought in one of these passages If its a fresh rebulid.
 
20/50 is the oil weight, not a complete rebuild. Just the oil pan gasket, new rear main seal conversion kit and valve cover gasket. Was reading on the pressure relief spring, but unsure of where it was located. Read about shiming it to see if the pressure increases or not. But cold it is 40psi at an idle, am going to take it for a 5 mile run tomarrow and see what it does under load and at operating temp. Have let it idle to normal operating temp after I put the engine back in and it was fine. The first road trip wasnt promising under load.

Will post tommarow what I find.
Thanks for reponding, if you can tell me where the pressure relief sping is located I will try shimming it and see what it does. Thanks again.
Dan
 
Ok,
I took her for a 10 mile drive today. Initally when I started it was 60psi cold at an idle and 70 at 2k rpm driving. After driving for awhile the engine temp was 3/4 to normal and the psi was 50psi. By the time the engine temp reached N it was down to 25psi at 3k rpm. And at an idle at the stop sign it was 10psi. When I reached the house it was the same 20psi at 2k rpm and 10 psi at an idle.

When I parked it and shut off the engine oil drained out the trannyies weep hole in a stream for 20 seconds. I resarted it the oil stream stopped and just dripped 1 drop every 2 seconds.

Now I am frustrated. Any Ideas?

Here are some pics:
1 1/2 years ago when I first got her.
01-28-08_0632.jpg


Sitting in the driveway
04-25-09_1051.jpg


Engine left side, notice the capped valve cover line and the pcv valve.
04-25-09_1053.jpg


Engine right side, I added an electronic distributer. You can see the capped valve cove line better.
04-25-09_1054.jpg


Engine top side, new master brake resivoir, also all new brake lines.
04-25-09_1055.jpg


The dash foam was cracked and split, so I stripped it to the metal blnking plate and covered it with 1/2 in foam and vinyl, I like the trimmer look.
04-25-09_1803.jpg


Back side, ignore the mess in the garage :p
04-25-09_1057.jpg


Had a heck of a time painting these rims, I ended up making a template out of steel and cutting the curves out of tape and laying them on in layers. 4 finger, and 8 curves for the clover leaf pattern.
04-25-09_1056.jpg


This morning in sunny alabama! Beautiful day.
04-25-09_1119.jpg


Well if you have any Ideas why when the oil gets hot my pressure drops that drastically I am all ears!
 
If I was a betting man I would say rod end bearings. But there are lots and lots of things it could be.
 
Sooo... you never drove the car with this engine before putting the oil seal kit in it?

I'm with Jack and suspect worn bearings.
 
Is that actually a PCV valve there in-line? It looks more like a common "check valve" (one-way valve) which would be counter-productive in this case and would cause the oil leakage problem that you are talking about (and I agree with Jack that it sounds like the rod bearings are getting worn).
Thinking about it-- your oil pressure should be spiking at idle-cold and should not go up (cold) when you rev it, I am beginning to think that you DO indeed have a bad pressure relief valve and should look into replacing it with a 1/2" ball bearing and try it again.
Bill
 
I was afraid of that, was hoping for somthing simple, like a worn pressure relief valve spring. That looses its tensile strength when it gets hot. If I shim it to test would that tell me anything?
Dan
 
Nope never drove it long distance, just up the driveway etc and didnt drive it long enough to notice the oil pressure.
Dan
 
It is an actual PCV valve, from reading I saw people recommended adding one there to give neg pressure to the crankcase to help reduce or eliminate leaking. Is this not the correct set up? Any advice on PCV valves would be appreciated. It has been a long 1 1/2 years, I don’t might a little inconvenience but answers help :p
Dan
 
scubabatdan said:
I was afraid of that, was hoping for somthing simple, like a worn pressure relief valve spring. That looses its tensile strength when it gets hot. If I shim it to test would that tell me anything?
Dan
Click to expand...
If I were you I would inspect that valve and the one on the filter housing if it has one. You could shim it but I think its stuck open or there's something caught in the seat. I always check the easy stuff first.
 
I had oil pressure problems on our AH 3000 - turns out it was the oil relief pressure spring. I should have a 1275 cc block in the garage; if so, I'll find the oil relief thing and pull it tomorrow and measure its length. On the 3000, the spring we had was about 0.25 inch (if memory serves) shorter than the new one I ordered, and the increased pressure from the longer spring kept the metal to metal seat in better contact and prevented the oil from bleeding back into the sump when operating normally.
Shimming yours will give you an easy check as well - and I fully concur with Chris: check the easy stuff first (particularly the cheap, easy, stuff).

Doug
 
You can get or make an adjustable nut for the oil pressure spring. This will allow you to set the pressure to your likeing.

Miss Agatha has one.
 
The pressure relief valve can adjust cold oil pressure to a higher setting, but it won't help any once the oil gets hot, seeing that you had as much as 70 psi cold, my thoughts are the same as Jack, worn rod bearings, even .0005" -.001" extra wear can mean low oil pressure, a wron bearing is allowing bleed at the rod thrust side too quickly, and these motr, oil pressure wose are very sensative to rod journal clearences. I build all street engine at .0015" rod and main, and my race engine at .002", vary that even a .0005" and you'll see a oil pressure decrease at the gauge, same thing happen when the bearing wears.

Did I read you to say you put the rear seal kit on a 1275, I hate to tell you this, but I never saw one of those work for any amount of time.

Also you be much better served, brething your crankcase to line going to a ctch tank with a breahter on it, or a breather, rather than trying to suck it thru that itty-bitty line going to the DCOE, these engine need to breathe, especially one with a lot miles on the rings, if you don't let it breath, it will find a way to leak where ever it can breach.
 
I will inspect the valve and spring and try the shim technique, LOL but I am not hopeful :smile: Just not my luck.
Thanks
Dan
 
From the book it is not suppose to be less than 2.86 innches in length. I will check it, I was also thinking of making a jig and hooking it to a lbs scale and pulling it down the legnth seated. Then apply 180 temp to it with a heat gun and see what the lbs scale does. That way I see if it looses any lbs of pressure at 180 degrees. Hey I had a Mcgyver moment... :p
Thanks,
Dan
 
Design please :smile:
Thanks Jack
Dan
 
The interesting thing is it showed the breather line connected to the valve cover and it really leaked then. I talked to Jack and he suspects that the leak is comming from the oil pump cover since I did not do anything to it when I had it apart. After I connected the PCV valve the leak diminished, hmmm have read on the catch can, but no vacum to put neg pressure on the crank case? I will give the shimming a try on the spring but I think you and Jack are right. If it doesnt work I will try the bearing putty Jack was talking about to find out what my gap is in the rod ends and main bearings.
Thanks!
Dan
 
Dan - just got in from the garage: pulled the oil pressure return springs from a 948 cc engine (runs very well, good oil pressure) plus a 1275 cc block that I've never run.
The 948 spring length was 2 3/4 inches long; the 'bullet' that makes contact with the block showed some wear but looked ok; the 1275 spring was 1/16th inch shorter at 2 11/16 inches overal length.
I've heard (on the 3000 site) of folks stretching their spring to make it longer and thus increase the pressure on that metal to metal seat, so you might want to try that if it's easier than shimming.
If you don't have enough spring pressure, your cold oil pressure can still look good but once it warms up and thins out a bit, the poor seal between the block and the 'bullet' will let too much oil bypass back to the sump and your hot oil pressure will drop.
It's the bolt head on the side of your block, just above your starter, and takes a 1 inch socket. If you've got a Datsun 5 speed, you'll have to use a spanner if you're British; wrench if you're not as there isn't enough clearance to fit a socket.
I was panicked that our AH 3000 was going to need a bottom end teardown because of similar oil pressure problems, but they all went away when the spring was replaced.
I'd send a picture, but don't know how to attach - advice please, someone!
Good fortune.

Doug
 
Thanks Doug, will check it out and get back with an update.
Thanks
Dan
 
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