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MGB MGB 1977 oil pressure problem
- Thread starter Arky_1
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rick_ingram
Yoda
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What pressure does the engine run at idle as well as at speed after it's warmed up?
ronzet
Jedi Knight
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Arky_1,
When the car is cold the viscocity of the oil is high and thins as the engine warms up...
Although an oil pump is a <span style="font-style: italic">possible</span> cause...
The symptom that you have described is indicative, in general, of worn rod and main bearings that have excessive 'lash' between the bearing and the journal...producing oil leaking around the journal and the subsequent drop in OP as the oil becomes thinner when heated...
The good news is that you will now have a chance to see what the inside of the MGB engine looks like..
When the car is cold the viscocity of the oil is high and thins as the engine warms up...
Although an oil pump is a <span style="font-style: italic">possible</span> cause...
The symptom that you have described is indicative, in general, of worn rod and main bearings that have excessive 'lash' between the bearing and the journal...producing oil leaking around the journal and the subsequent drop in OP as the oil becomes thinner when heated...
The good news is that you will now have a chance to see what the inside of the MGB engine looks like..
tony barnhill
Great Pumpkin - R.I.P
Offline
Well, before anybody suggests he jump in & start disasembly, there are still lots of questions to answer - & as he's new to MG's, we need to go slowly on this one.
Some good questions already posed...let's summarize & answer these in order:
1) what type oil is in the engine (20w50, 10w30) & how long's it been in there?
2) what's the oil pressure when first started - idling & at speed?
3) what's the oil pressure when the engine gets to normal operating temperature - idling or at speed? [think that's been answered: 10psi idling or at speed]
4. what's the compression - taken dry & then taken wet?
5. can you do a "leakdown test"?
There may be more, but that's a start.....
Some good questions already posed...let's summarize & answer these in order:
1) what type oil is in the engine (20w50, 10w30) & how long's it been in there?
2) what's the oil pressure when first started - idling & at speed?
3) what's the oil pressure when the engine gets to normal operating temperature - idling or at speed? [think that's been answered: 10psi idling or at speed]
4. what's the compression - taken dry & then taken wet?
5. can you do a "leakdown test"?
There may be more, but that's a start.....
ronzet
Jedi Knight
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Arky_1,
Along with the questions that Tony has tendered and his admonishment to think and check before tearing apart...
When warm... If you accelerate does the noise of the valve clatter increase dramatically? As the OP drops, the ability of the pump to move oil to the top end decreases and will precipitate oil starvation to the valve rocker assembly, particularly under load or at higher RPMs.
My '66 B has a similar condition -- that is, 55psi when cold, 8-10psi when warm -- regardless of the RPMs...valve clatter increasing with load or high RPMs when warm....
In my case I know that the lower end needs rebuilding. A while back I dropped the pan and plasti-gauged the bearings and found the lash tolerance was WAY outside of the acceptable clearance. TO BAND-AID the problem, I replaced the inserts with a new set that were the same undersized (or oversize to be exact)(.030 under/over)that were in it. Tolerances were a little closer but still outside of max tolerance. This bought me a little time with an increased warm OP for a few hundred miles. The operative word here is <span style="font-weight: bold">BAND-AID</span>...
The crank in my B needs milling and the bearings (main and rod)need to be replaced with correct size for proper tolerances...
This will be part of a total rebuild of the bottom and top end of the engine. In my queue of things to be done.
I do not drive the B much and drive it gingerly... My A is road worthy (although currently bent) and satisfies the urge to drive an LBC... The B restoration project will start a little later this year...
Along with the questions that Tony has tendered and his admonishment to think and check before tearing apart...
When warm... If you accelerate does the noise of the valve clatter increase dramatically? As the OP drops, the ability of the pump to move oil to the top end decreases and will precipitate oil starvation to the valve rocker assembly, particularly under load or at higher RPMs.
My '66 B has a similar condition -- that is, 55psi when cold, 8-10psi when warm -- regardless of the RPMs...valve clatter increasing with load or high RPMs when warm....
In my case I know that the lower end needs rebuilding. A while back I dropped the pan and plasti-gauged the bearings and found the lash tolerance was WAY outside of the acceptable clearance. TO BAND-AID the problem, I replaced the inserts with a new set that were the same undersized (or oversize to be exact)(.030 under/over)that were in it. Tolerances were a little closer but still outside of max tolerance. This bought me a little time with an increased warm OP for a few hundred miles. The operative word here is <span style="font-weight: bold">BAND-AID</span>...
The crank in my B needs milling and the bearings (main and rod)need to be replaced with correct size for proper tolerances...
This will be part of a total rebuild of the bottom and top end of the engine. In my queue of things to be done.
I do not drive the B much and drive it gingerly... My A is road worthy (although currently bent) and satisfies the urge to drive an LBC... The B restoration project will start a little later this year...
Bob Claffie
Jedi Knight
Offline
No one has mentioned the possibility of a tired gauge or sender. Don't take the engine apart because maybe-----something is wrong or going wrong. Old rule of thumb was 10 pounds of pressure for every 1000 rpms. Ten pounds at idle is not necessarily bad. Years ago I had a new Alfa that idled at zero. Dealer mechanic said no problem as at idle there is no strain on the motor. Never had a problem in 10 years. Bob
ronzet
Jedi Knight
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Bob,
I think that we all have a propensity to 'think the worse' and jump before we look....
A bad gauge is certainly a <span style="font-style: italic">possibility</span>. Another possibility is a faulty oil pressure release valve....
Other than that, I can think of nothing that has these symptoms other than worn bearings.
Although I do jump before I look all too frequently, in this case eliminating the easiest (and lowest cost) issues first is the order of the day... As in chaging oil and filter, then borrowing a gauge from someone, then possibly a release valve, then, when all else fails, yanking that puppy out for a rebuild....
I think that we all have a propensity to 'think the worse' and jump before we look....
A bad gauge is certainly a <span style="font-style: italic">possibility</span>. Another possibility is a faulty oil pressure release valve....
Other than that, I can think of nothing that has these symptoms other than worn bearings.
Although I do jump before I look all too frequently, in this case eliminating the easiest (and lowest cost) issues first is the order of the day... As in chaging oil and filter, then borrowing a gauge from someone, then possibly a release valve, then, when all else fails, yanking that puppy out for a rebuild....
ronzet
Jedi Knight
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Tony,
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]4. what's the compression - taken dry & then taken wet?
[/QUOTE]
Since I am always interested in learning something new, especially from a Guru...
Please elucidate me to the relevance of #4 to the symptomology..
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]4. what's the compression - taken dry & then taken wet?
[/QUOTE]
Since I am always interested in learning something new, especially from a Guru...
Please elucidate me to the relevance of #4 to the symptomology..
twigworker
Jedi Trainee
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Tony is just trying to get an overall picture of the engine. Compression would obviously not impact oil pressure, but if the copression readings are low or vary greatly it might be another tick mark for going in to the lump.
I second the suggestions about further evaluation before stripping the engine. Oil and filter first, then introduction of a known good gauge during cold and hot running. Pain in ass as it might be, the removal and inspection of the pressure relief valve and spring, yada, yada.
That is of course, if you don't hear lots of whammin-n-frammin. A highly technical term used only by "those in the know". LOL In that case hard road testing and such could just exacerbate what ever problem there is.
I would go so far, since the car is new to the owner, to drive it at least enough to identify other problem areas. Transmission function, drive shaft clanking, rear axle noise/rear brake function, that sort of thing. Once everything is taken into account a better decision can be made about expenses, down time and overlapping repairs.
Jack
I second the suggestions about further evaluation before stripping the engine. Oil and filter first, then introduction of a known good gauge during cold and hot running. Pain in ass as it might be, the removal and inspection of the pressure relief valve and spring, yada, yada.
That is of course, if you don't hear lots of whammin-n-frammin. A highly technical term used only by "those in the know". LOL In that case hard road testing and such could just exacerbate what ever problem there is.
I would go so far, since the car is new to the owner, to drive it at least enough to identify other problem areas. Transmission function, drive shaft clanking, rear axle noise/rear brake function, that sort of thing. Once everything is taken into account a better decision can be made about expenses, down time and overlapping repairs.
Jack
tony barnhill
Great Pumpkin - R.I.P
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Castrol 20w50 - & they have it for engines with lots of miles on them.Arky_1 said:
Absolutely nothing - except, I'm gonna bet there's an engine teardown in his future & it'll let him know a little more about the condition of his head & rings - especially if he has to repair the main problem on a tight budget....& I just like to do all the tests possible before tearing one down!ronzet said:
Both are possibilities...however, I figured adding them to his questions to answer right now could complicate things as they're probably gonna ID the problem.....putting a penny behind the pressure relief spring will tell if its the problem; switching guages temporarily will also...but, if you're new to the hobby, I figured "KISS".ronzet said:
tony barnhill
Great Pumpkin - R.I.P
Offline
Ron - I think you & I agree on the potential teardown....if he really needed to $$-wise, he could redo the rod/main bearings without removing the engine - especially if rings/valves were good....<span style="font-weight: bold">if he's on a tight budget</span>...but, were it me, I'd be prepared to do bearings/rings/valves, etc. at the same time....but, I still like to know everything I can about an engine before tearing it down.
tony barnhill
Great Pumpkin - R.I.P
Offline
Doc, even after I find out to what specs the machine shop is cutting the crank, I still use plastiguage on the bearings to check them! & I just had a Midget block bored 20-over but will still mic the new ring gaps before I install them on new pistons...& I'll do compression checks after its put together....you can never know too much about an engine - before you disassemble it, during reassembly, & after!!