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MGB At what oil pressure do I need to dig into the engine?

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drooartz

drooartz

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The oil pressure in my MGB has been pretty consistent in the 3 years I've been driving it. On start up it's near 60, once fully warmed up and at speed it's around 42/45ish. I need to run a compression test when I get a moment, but otherwise the car runs pretty well and seems to pull fine, though I don't have much to compare to.

At what oil pressure levels do I start thinking about new bearings/rings? I've no idea how many miles are on this engine, or if it's ever been rebuilt -- though the head is not original so I expect is has been gone through at some point.

The long term plan is to assemble a second engine, purpose built for a supercharger, but that's a ways off.
 
No expert, but were it my car and with the long range plans you have, I'd leave well enough alone and drive it as is until the new engine is ready to go in. Those numbers don't warrant tearing into it, IMO.
 
Gotta agree with Mickey on that. If it smokes, well, that's a diff'rent kettle o' mullet.
 
No smoke, oil level is reasonably steady (other than a few leaks here and there, just typical stuff).

Mostly wanted to make sure I wasn't doing any other damage -- I'm realistically a little while from the engine swap, but want to keep driving while I'm gathering parts (and money).
 
If you're not already using 20W50 oil, you might want to change over. Can't beat good ole Castrol GTX.
 
I have a friend that drove a bigger Brit-car with a 3.5 liter straight six for 10 years with oil pressure about 20 while driving and around zero at idle. Would have worried me, but he never gave it a thought. Of course, he didn't drive it like I drive my B-GT...
 
Old rule of thumb was 10 lbs of pressure for every 1000 of RPMS. Each engine is different, my Dad had a new '66 Alfa Gulia that hot idled at zero- never a problem. My Chevy is 80 ish at cold start up, cruises at 40 and idles when warm at about 5. Been doing it for the last 12000 miles. Don't try to fix something that isn't broken. Bob
 
Drew........whatcha doin? If it ain't broke, don't fix it. :smile: No need to go looking for trouble with our beloved little cars - if/ when it wants to, trouble will come knockin'! :smile:
 
Mickey Richaud said:
If you're not already using 20W50 oil, you might want to change over. Can't beat good ole Castrol GTX.
Click to expand...
Already running 20W50 VR1

Silverghost said:
Drew........whatcha doin? If it ain't broke, don't fix it. :smile:
Click to expand...
My running issue is that I don't always know what "ain't broke" looks like. My minimal experience with old cars means that while I can read the information coming in (from gauges, car noises, etc), I quite frequently have no bloody idea what to do with that info. So I figure I'll ask before I am forced to learn the hard way. :smile:

I'm certainly not looking for issues, I'm quite confident that the issues know where I live and can find me at any time. :grin:
 
Alfas are notorious for running lower oil pressure. The MGB engines seem high to the Alfisti.

As long as you keep the oil changed it should be fine.
 
Just my two cents. I drove my Dad's 1977 MGB from Arizona to North Carolina over the July 4th week. It was 2200 miles and I used 22 quarts of oil. The oil pressure when engine was at full mark read 70-75lbs, when the oil was VERY low (didn't know I was using that much oil on the first leg) the pressure dropped to under 25. I do not see any smoke and there is no obvious leakage. The head and block are covered with a fine glazing from leakage around the head gasket. My dad had put in "super hot" plugs to keep the fouling down. I am going to replace the rings and pistons (if needed), hone the cylinders (if not scored), and rework the head myself (if not damaged). I think this will get me by for now (also inspect the crank, and camshaft). Hope to do this quickly and as I am doing the work myself inexpensively. Basically the engine needs rebuild badly enough that in 200 miles the pressure drops from 75psi to around 40 or so.
 
Boggsy64. Had a similar experience a number of years ago. On a (relatively) high speed trip from Ma to Ga and back we used a quart per 100 miles both ways. On tear down it was found the rings were frozen in the ring grooves, ONLY problem , new rings plus hone and all was good again. The tired engine was in a 6 or 7 year old honda civic with 70K on it ! The point I want to make that a total rebuild may not be necessary. Bob
 
Also, keep in mind the simple fact that your oil pressure gauge might not be accurate. If you think the oil pressure is low, be sure to check it with an accurate gauge before making any conclusions.
 
A fresh MGB engine runs at 80 psi ( at the limit of the valve) when started and holds 50 at an idle hot. A good indication of bearing wear would be how quick the oil pressure came up when the engine is started from cold. I've got 95,000 mi. on the 69 B and I put rod bearings only in it at 80,000 ( they rattled when the engine was first started up). It still holds 50 psi or better when running and I don't drive it really hard so I'm sure it will last awhile. Yours sounds a little low but if it isn't noisy and doesn't use oil why bother yet? The rod bearings are the first to wear out and easy to change.
 
DrEntropy said:
Alfas are notorious for running lower oil pressure. The MGB engines seem high to the Alfisti.

As long as you keep the oil changed it should be fine.
Click to expand...

MGB oil pressures also seem high to those experienced by MGC owners! My newly rebuilt MGC engine achieved 52psi at speed and between 15psi & 20psi at hot idle!
 
Ye ol workshop manual says: 10-25 lbs/sq in at idle & "running" 50-80 lbs/sq in. BTW, Les Bengston had a great write up on performing a compression test. If you can't find it on the web let me know.
 
It's a PITA but you may want to change the bypass spring/bullet and see if that brings up the pressure a bit. That said I drove a 70 MGB for several years with 40 lbs at speed and no issues.
 
Drew, if you see the oil pressure going further down in the future, take that as sigh you have excessive rod bearing wear, once the clearance gets bigger from bearing wear the oil slips past the rod bearing too quickly,, this lowers oil pressure.
 
Thanks. Pressure has been stable since I bought the car, but I'll keep an eye to see it doesn't slip farther. I'm currently gathering parts for a replacement engine (supercharged) so I can swap and not loose too much driving time. Hopefully the current engine will give me another year or two, and I expect it will.
 
Well as long as it holds what it's got, that is more likely to tell you, it just has tad too much clearance and not necessarily a worn rod bearing deal, of course you can change rod bearings in a MGB with out removing the engine, the front bolts on the oil pan are somewhat of a pain to get to, but people do it.

This sort of thing is why I go the extra mile blue printing clearances on the crank bearings, and build street engine with .0015" rod and main clearances, is to keep oil pressure at a premium, as little as .0005" extra clearance can affect the oil pressure as much as 10 psi. This is why one should always have the big ends on the connecting rods checked, and re-sized if needed, because they are the other part of this equation, and I almost always find the connecting rods need to re-sized.
 
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