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Oil pressure

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Raggood1 Rick Gooding
Sparta, MI - Michigan, USA   USA
Hooked two separate gauges to the line coming out of the block...zero oil pressure...what next?

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course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
I'm sure you'll get more knowledgeable answers from other responders, but, I'd guess the suspected causes in order of easiest to fix would be:
1) (The doh!, how did I do that answer) No oil in the engine.
2) Assuming that you are checking oil pressure at the fitting that connects to the flex hose that goes to the oil pressure switch (or oil pressure sender depending on the year of your car), if you're lucky, maybe that fitting is just plugged.
3) The oil pressure relief valve may be stuck open or it's spring may be broken. I think it's on the lower, aft, drivers side of the block.
4) The oil pump could be clogged or worn out and you'll have to pull the sump to check it out and repair (I don't know if that can be done with the engine in the car).
5) The oil passages in the block could be clogged. I think that requires an engine pull, dissassembly, boiling the block, and perhaps cleaning out passages mechanically.

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
I believe you said you were driving for a half hour with 55-60 psi oil pressure and that it abruptly dropped to zero. Is that correct? If so, and if you have no nasty noises, it can only be a mechanical failure of some sort. Perhaps your oil pressure relief valve is stuck open. This does not happen nearly as often as folks fear, but it is certainly possible. I'm sure you've already checked the oil level.

The oil pressure relief valve lives behind a one inch hex plug on the carburetor side of the engine, low and toward the rear of the side of the block. It is the only one inch item on the engine. When you unscrew it, spring pressure will push the cap away from the block when you reach the last threads, but it is not violent nor dangerous. Just be prepared for some spring pressure. It is easily managed by hand.

With the spring out, you should be able to remove the small valve itself with just hand pressure. If it's stuck, you may need to try other means. But I would definitely remove and inspect it.

If the valve is not at fault, then the only other thing that comes to mind is a mechanical failure of the oil pump or the oil pump drive gear. You'll need to drop the oil pan in order to remove and inspect the oil pump and its drive gear...

Dick

In reply to # 3514192 by Raggood1 Hooked two separate gauges to the line coming out of the block...zero oil pressure...what next?



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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Raggood1 Rick Gooding
Sparta, MI - Michigan, USA   USA
Thanks for all the advice from everyone...even though it makes me sick

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
If it's a stuck oil pressure relief valve, it's not a big deal. Toughest part is getting the one inch threaded cap started back into the block against the spring pressure. It helps to have a buddy and some patience. But not a big deal...

Dick

In reply to # 3514227 by Raggood1 Thanks for all the advice from everyone...even though it makes me sick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

rocannon Avatar
rocannon Platinum Member Frank L
Inconveniently located in the wilderness, Oklahoma, USA   USA
1967 MG MGB GT "GT From Hell"
1980 MG MGB "Restored By Photoshop Inc."
Which line? The big one will measure the oil pump pressure. The small one will measure the main galley oil pressure.

In reply to # 3514192 by Raggood1 Hooked two separate gauges to the line coming out of the block...zero oil pressure...what next?



“Yes, another great idea destroyed by a simple set of facts."


“Often, quotes not actually written or spoken by Mark Twain are attributed to him, because it lends those quotes an undeserved respect. Not this one, though. He must have said this one. I mean, look, it has his name after it and everything.”

~ Mark Twain



TANSTAAFL !



Edited 1 time(s). Last edit at 2017-05-18 05:50 PM by rocannon.

Raggood1 Rick Gooding
Sparta, MI - Michigan, USA   USA
Hooked to flex line coming out of block

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fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
If that's the small line next to the big hose/pipe, then remove it at the block. Crank(or start) the engine for up to 30 seconds. If oil gushes out, you have a collapsed hose. If no oil then it's into the engine for further investigation.


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preperation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
rocannon Avatar
rocannon Platinum Member Frank L
Inconveniently located in the wilderness, Oklahoma, USA   USA
1967 MG MGB GT "GT From Hell"
1980 MG MGB "Restored By Photoshop Inc."
Assuming you're turning the engine over with sparkplugs out...


Now hook up the gauge to the large connection next to the small line connection. If you get good pressure, you can be sure the oil pump and pressure relief valve are ok.
If you can't connect the gauge, then disconnect the end of the hose at the oil filter base, direct the end of the hose into a good sized container, and crank the engine over. If you're lucky you'll get a good stream of oil coming out of the hose. You'll know then that at least the pump and pressure relief valve are letting oil get to the filter. You won't, of course, know the pressure.

If you don't get good/any oil pressure or any oil flow, I'd drop the pan and inspect and measure clearances on the oil pump. If the pump checks out as good, that leaves the pressure relief valve as the likely problem.

In reply to # 3514274 by Raggood1 Hooked to flex line coming out of block



“Yes, another great idea destroyed by a simple set of facts."


“Often, quotes not actually written or spoken by Mark Twain are attributed to him, because it lends those quotes an undeserved respect. Not this one, though. He must have said this one. I mean, look, it has his name after it and everything.”

~ Mark Twain



TANSTAAFL !

fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
The only oil pump issue that would cause going from decent hot running oil pressure to zero would be a sheared pin between the inner rotor and the shaft.


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preperation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
Tar Trekka Avatar
Tar Trekka Ross H
Sydney, NSW, Australia   AUS
1968 MG MGB MkII "Miss B"
Hi there,

Check out the John Twist Video Clip.

Most Important, if you remove the Oil Pressure Relief Valve, mark where the thread on the Plug engages, before you try to re refit it.

It makes it a lot easier when re fitting the Plug.

I had a Mate up top, pushing the Plug into the Thread with a length of Timber.

It certainly made a "Bugger Of A Job" a lot easier.



Ross H.

Any day above the ground is a great day, especially "Driving Miss B".

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rocannon Avatar
rocannon Platinum Member Frank L
Inconveniently located in the wilderness, Oklahoma, USA   USA
1967 MG MGB GT "GT From Hell"
1980 MG MGB "Restored By Photoshop Inc."
I see in your other thread on this same issue you're thinking of pulling the engine.

A bit premature, in my opinion.



“Yes, another great idea destroyed by a simple set of facts."


“Often, quotes not actually written or spoken by Mark Twain are attributed to him, because it lends those quotes an undeserved respect. Not this one, though. He must have said this one. I mean, look, it has his name after it and everything.”

~ Mark Twain



TANSTAAFL !

Raggood1 Rick Gooding
Sparta, MI - Michigan, USA   USA
The car has 78000 miles on it and I believe to be a good time for bearings and a new pump...plus I have help right now to do the job...then I know what I have

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
You can replace the oil pump, all of the rod bearings, and the three center main bearings by dropping the oil pan and not having to remove the engine...

Dick

In reply to # 3514838 by Raggood1 The car has 78000 miles on it and I believe to be a good time for bearings and a new pump...plus I have help right now to do the job...then I know what I have



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Raggood1 Rick Gooding
Sparta, MI - Michigan, USA   USA
Kinda hard for a 67 year old man to do it from lying on a garage floor...especially the pressure relief valve will be easier with engine out of car...let you know more first of next week...not starting job until Tuesday

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