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MG Midget and Sprite Technical - A Series Oil Pressure ( or the lack of !)

Not posted in ages as life, once again got in the way.

I bought a 1275cc A series engine of eBay, it was n't complete.

Not an issue as I had plans for it, so quite a few years later it now has...

A Peter Burgess head, high ratio roller rockers, lightened flywheel, new kent cam and oil pump, reground crank and new bearings, new OPRV and spring, new std oil filter housing with bypass valve, new water pump..

I assembled the engine sometime ago and dropped it into my Sprite last year, spend far too long trying to get oil pressure - checked and swapped things like OPRV and spring, bled/primed the pump etc, gave up and pulled the engine out this year, tore it to bits to find the ground crank had been supplied with std mains bearings !!!

Rebuilt the engine last week,checked the new bearings were correct, refilled with oil ( 20w50 ) with graphogene on all bearing surfaces, hung it in the crane connected the starter and STILL NO OIL pressure - help !!!

What am I missing ?

Thanks
Malc Gilliver

How incomplete was it?

It does have a pick-up pipe/strainer, doesn’t it?

How did you prime the pump?
Dave O'Neill 2

How long did you crank it?

Trie a different gauge?

Is oil reaching the rockers?

anamnesis

Hi Dave, yes it had a strainer and due to age and cars I had a spare - that's all fitted.

I hasten to add, there is oil being pumped, but no pressure - it was seeping out the banjo bolt, then filter head, once tightened they were fine.

Primed the pump by filling through the banjo bolt hole.

Hi anamnesis, cranked on the engine crane - so can't check for oil at the rockers, at the moment.

Cranked about 4 times till for maybe 5 seconds a time - I will time it the next time I crank

Tried two different oil pressure gauges - 0 reading on both, even with larger diameter hose feed.
Malc Gilliver

How is the oil pressure overflow valve/spring?
Flip Brhl

I bought new and fitted that, then swapped it for the old setup- valve and spring
Malc Gilliver

Assuming no faults anywhere, a new build might need a fair bit longer than 5 secs continuous cranking to fill all the galleries and under pressure spaces. And needs fast cranking.

Plugs out. Spin it for 30 secs plus. Since you know oil is flowing, without any combustion pressure on the rod ends, it won't do any harm.
anamnesis

Thanks, I am hopeful, I have left the battery on charge and will time each run next time - I am considering using the battery on the Skoda - start the car - leave running and run cables of that, it was late in the afternoon.

Malc Gilliver

I agree with Anam. My 1275 was rebuilt and sat on a shelf for several years (turned manually regularly with oil in bores). Fitted to car, filled with oil, primed, spun on starter (plugs out) and waited maybe 30 seconds and pressure came up on gauge. 5 seconds isn't enough. It's slightly nerve racking but you have to trust the process.
Bill B

Hi Bill,

Thanks for the info, I didn't measure the time, so I am guessing and like you say it feels like hours but it did crank it four or more times, tbh, I assumed that once I had fixed the bearing issue it would just work, I have to say, that even with the issues on the bearings, the graphogene seemed to protect everything.
Malc Gilliver

It could also have an airlock in the pipe to the gauge. I have had that. Just undo the pipe turn it over until oil comes out then reconnect.

Trev
T Mason

Malc---Where are you measuring the oil pressure from--
I got caught once with a filter housing off an auto 1100 that found it's way into my possesion-
Had the gauge hooked into it where a switch had been and couldn't get pressure----found out that the warning switch on an auto only operates if the filter is blocked because of where it is on the housing---maybe if your engine was a basket case you might have an auto housing ---long time ago but I think it had two holes, one for the pressure gauge/light and one for the warning light---as i said long time ago but there was an issue with the housing there--
Cheers
willy
William Revit

Hi Trev,

Yeah I wondered about that, so cranked it without the gauge fitted till oil came out - thanks

Hi Willy,

I am using the oil pressure gauge tapping next to the banjo, I had to buy an oil filter housing, that had no takeoff for the gauge

FWIW, the gauge is the 1965 type - ie has an direct oil feed to the gauge with also has the capillary for water temp
Malc Gilliver

Here, right Malc?


anamnesis

Yes, exactly there - I even recognise the diagram ! having studied that and Vizard till I went cross eyed !
Malc Gilliver

Willy
The mk 11 and very early mk3 1275 also had the blocked filter light at the top of the dash.
richard b

Cranked the engine for a measured minute, then opened the banjo bolt and turned the crank by hand backwards about 20 times, then turned it the correct way and the oil came out of the port, refitted the banjo bolt, cranked the engine by hand till oil ran out of the oil pressure pipe, reconnected that to the oil pressure gauge and cranked the engine for a full two minutes and ….. NO OIL PRESSURE!!!

Help me before I go looking for a suitable Honda engine for it 🤷‍♂️
Malc Gilliver

Could it be the gauge or its connections?
Jeremy MkIII

New oil pump? New gasket? Bolts tight?

Double checked pressure relief seating properly?
anamnesis

If oil came out of the oil gauge block tapping when turning by hand - try disconnecting the oil gauge and spin the motor on starter - oil should shoot out of block tapping hole.
richard b

The answer is at hand ………when I fitted the engine and found no oil pressure I used the original AHSprite oil pressure gauge. That was a function of the bearings being the wrong size, i then rebuilt the engine and used an old Mini oil pressure gauge, I have two of them and neither registered pressure, I did this because the gauge in the car is the dual oil pressure and engine temperature with a capillary feed and I didn’t want to disturb it, anyway in a fit of “ what the hell !” So I took the original gauge out of the dash the fragile capillary feed and sure enough I have 50psi on cranking!!!

So I have two broken/untrustworthy gauges !!!

Thanks for all your help, time to stuff the engine back in !!!
Malc Gilliver

Malc,

A good result. Any chance of you getting an image or 2 of the guts of the failed gauges? Not much to go wrong with a Bourdon gauge unless the gearing has become detached or failed.
David Billington

The Bourdon tube can get bent.
Yes, I know it is supposed to be bent, but I mean they can get deformed.
GuyW

Tbh, I am kicking myself over this, but the original gauge is from 1965 and the other two are 1970’s oil gauges out of old Minis, the fact that both showed no oil pressure after the first one seemed to confirm the fact, so I am keen to know why they both appear to have failed
Malc Gilliver

May be something as a stuck movement. Internal corrosion for example.

But likely as Guy said. Internal tube is damaged in some way.

"The gauge contains a flexible coiled tube called a bulb, the open end of which is rigidly mounted to the gauge's outer casing. The other end of the bulb is closed and connected by a lightweight linkage to the bottom end of the needle, which is itself mounted on a pivot.

Oil is fed into the bulb from the supply pipe at very nearly the same pressure as it left the engine. The bulb tries to straighten under the pressure and in doing so moves the needle around the calibrated gauge scale . The greater the pressure, the more the needle moves."

Or maybe the pivot is seized.

What brand? Smiths?

anamnesis

Yes, Smiths gauges, probably off a 1000cc Mini that I had in the mid 80’s
Malc Gilliver

Wouldn't be kicking yourself too hard Malc. It's just part of the journey.
If you have op now and both gauges are dead then it's either both gauges are dead or the fitting between the gauges and the block is blocked or too long and bottoming out in the oil gallery---all a bit strange but:
William Revit

It must be something in the gauges as I used the new hose I had made- the old metal tube snapped, so it’s literally the same installation for all the gauges, strainer onto the end of the hose. I’ll have a look once the car is back on the road.
Malc Gilliver

I am having similar oil pressure issues on my 1275.

Just changed the oil, and fitted an oil cooler (was previously fitted, but removed it when electric fan went in). Engine not run for @ 6 months.

Oil cooler filled with oil, and both pipes filled when connected. oil filter filled before fitting.

Cranking on starter with plugs out, and oil pressure gauge feed pipe removed shows "spurts" of oil coming out, after I stop cranking.

I did run the engine,gently, up to temp, and eventually the pressure went up to @ 30psi (but normal on startup was 40-60)

I could feel both oil cooler pipes had warmed up, and the filter, so something is pumping around.

Tried again today, and pressure at 0 again.

Never had this issue before, even after stripping down the engine - 5 years ago, rebuilding it, and fitting with oil cooler (this after 20 years) I got good oil pressure straight away.

Suggestions and ideas welcome :)
Tim Carter

Few random thoughts:-

Check if the oil pressure relief valve is clean and free of any grit etc. Maybe sticky as not run for 6 months ?

Do you have another gauge ?

If a canister filter I have heard of issues of not flowing properly (you said you had changed it). Maybe replace it ?

Assuming no leaks - as it has run pump should be primed - could try re-priming.

When I bought a cooler kit for a 1500 I was amazed to find swarf in the sandwich plate - I know you don’t have one but maybe worth checking the cooler flow.

Rather strange one - will watch with interest - best of luck.

richard b

Richard,

When I bought a Mocal oilstat I found quite a bit of swarf inside, I assumed the red caps were to keep dirt out rather than swarf in.

Tim,

Do you have an oilstat in you cooler installation?
David Billington

PR valve may be next port of call, got to at least remove the distributor to get a spanner on it.

Where to prime the oil pump ? if it is the "flow" to the oil cooler (nearest the back plate) then this was full of oil

Have a screw on filter

Don't believe I have another gauge - will take another look in the box of bits

No oilstat

Tim Carter

Tim,

Do you plan to get an oilstat, running without one is not a good idea as the oil may not get up to a proper working temperature in normal use, I presume this is a road car.
David Billington

In the day my daily runner had a cooler and in winter just put some Ali foil over the cooler.

I still don’t have a stat (most of the kits only had jubilee clip hose connectors ! ) but it is warmer weather running now for me !

Interestingly BMC never fitted stats to the MGB’s that were fitted with coolers from about the 70’s.
richard b

Tim,

You prime by undoing the banjo bolt that holds the oil feed to the oil filter.

You'll have to pull OPRV make sure it isn't jammed open, or the spring has snapped.
Malc Gilliver

“ Interestingly BMC never fitted stats to the MGB’s that were fitted with coolers from about the 70’s.”

They didn’t fit them to Spridgets either, although I believe the cooler was an option through most of production, certainly for the home market.
Dave O'Neill 2

"You prime by undoing the banjo bolt that holds the oil feed to the oil filter."

I don't have the banjo bolt anymore, or the pipe to the oil filter, these are replaced by the flow and return pipes for the oil cooler.
Tim Carter

Sorry - I haven't fitted an oil cooler to Spridget

So you take oil straight from the pump and put it through the oil cooler, then where - back into the filter and on in to the oil pressure gallery ?

What grade oil are you using - 20w50 ?

As the oil cooler worked before and doesn't now that imples to me that it is blocked - if you can remove the cooler and run the engine, if the pressure is back then your cooler or a damaged hose is the issue.
Malc Gilliver

I had a RWA midget in the late 70's. It had been factory fitted with an oil cooler from new. It didn't have a stat and was fine as a daily driver. I didn't bother with a stat whenI fitted an oil cooler to the Frogeye in the 80's and haven't had any problems
Bob Beaumont

Is it a new cooler or Second hand ?

Always a risk if you don’t know its history - if an engine has had a good blow up it’s good practise to replace the radiator element as it may well be full of crud and not possible to clean out effectively.
richard b

OPRV Checked, spring and plunger OK. What a pfaff, dizzy and starter motor had to come out to give access to the nut. For future reference, a 1" socket that wouldn't go on, was replaced with a long throw 26mm socket. Fun getting the nut back on given the strength of the spring ;)

The oil cooler has been on and off the car for 30 years, never been an issue before. As a last resort I could refit the banjo pipe and test...but oil does appear to be flowing in both pipes, flow and return from the oil cooler, they get warm when the engine warms up.

Oil coolers aren't one way are they? Could have fitted flow pipe to the return connector etc.?

Oil is Millers Classic Pistoneeze 20W/50
Tim Carter

Bob

I don't think an oil cooler causes a problem, it just over cooled oil robs the engine of power and costs more fuel, maybe the oils of the 60/70 couldn't run as high as more modern oils.

Tim

I feel your pain - I stood looking at my engine for hours trying to work out what I'd down wrong.

A quick WWW search and most sites says coolers are not 'handed'.

The oil pressure is a function of the mains/big ends clearances as I 'proved', if the oil cooler is restricting flow then it could mean the ORPV is dumping oil as that is on the same gallery as the pump, then flow to the oil filter is reduced and you have less pressure in the gallery, to me the next task if was my engine would be remove the oil cooler, of the pressure comes back the answer is in the cooler. But I nearly went mad trying to sort my engine out.
Malc Gilliver

I will do more testing tomorrow. Battery on charge so I can give full minute or more on the starter with plugs out, see what gives. If no progress then I will remove oil cooler and see what gives.
Tim Carter

I have a spare gauge (no temp sensor) I can send you but I’m sure your like me and want to fix it now !!!

I wouldn’t rule out a faulty filter it’s not unheard of. The MGB lads seem to use Mann filters but not seen any locally for A series.
richard b

I too discovered that getting at the OPRV isn't that easy, despite the fact that it just sits there, clearly visible. Must be one of those 'quick, 10 minute jobs' Not!

In my case I only wanted to check the spring length and condition of the plunger. I marked and removed the dizzy. Starter motor didn't need to be touched as I had a very large combination ring spanner that fitted. Once started a couple of flats and it just undid by hand. But putting it back was a bit of a tussle until I devised a way with a tyre lever and some chocks of wood to press the domed nut into position whilst I turned it to catch the first thread. Not the easy 10 minutes I had expected!
GuyW

Found an old dual gauge (thermocouple broken off). Cleaned it up and tested with football pump - got life from the needle. No spare pipe so will have to undo at dash and test from there.

Off to do testing with plugs out now. Almost too hot here to do anything...
Tim Carter

Now baffled!

Did the one minute starter test with plugs out.

Oil pressure went up to 40 and stayed there from 30 seconds on to the full minute. Good, I thought, it has sorted itself out.

Plugs back in, started the car. Oil pressure rose to 20 then slowly went back to 0, and then stayed there. After several minutes and a bit of gentle revving, no change to the gauge, which stayed at 0. No untoward rattles or knocks from engine.

Flow pipe a little bit warm, Return pipe still cool.

Why would I get 40 with plugs out, and 0 with engine running?

Next job then, oil cooler off and banjo pipe back on.
Tim Carter

Only way I can interpret that is - initial run, oil pumps enough oil to get pressure, then firing it up means much more oil ( oil vol = engine rpm ) and blocked cooler is forcing the OPRV open.

But I have to concede I have already 'decided' the issue is in the cooler - I reckonise that is probably wrong.

Re temp - I am impressed at your focus, I am sitting on a 2 ft dia fan with a chilled Stella having mentaly written the weekend off !
Malc Gilliver

PROBLEM SOLVED !!

and somewhat embarrassed...

As Malc and others said, the oil cooler might be blocked. Well, not quite...

To prevent oil spillage when moving oil cooler and pipes (all filled with oil) into position, I had plugged the ends of the pipes with suitable rubber stoppers. I had removed the stopper for the flow but NOT the return, and this was sitting happily in the top of the oil filter connection, preventing any proper oil flow. Didn't spot it when I had the pipe off previously, was checking for oil, which there was, so popped the pipe back on quickly, plus, it is dark down there!

Removed the little green bugger (I had wondered where it had gone...), refitted, started car, oil pressure of 60 at idle 700rpm.

Thanks to everyone for their help, consideration, support and guidance, and apologies for being such a numbskull.



Tim Carter

Easily done.
Dave O'Neill 2

Isn't that why they have check lists in surgeries to make sure that what goes in comes out again. Hopefully no damage done to the engine due to lack of oil when running.

Chatting to a neighbour recently and a mate of his race car was back together after a major engine rebuild and he took it for a test on the track and was complaining about all sorts of engine rattles but the problem was elsewhere, concern amplified every little tinkle and knock.
David Billington

Tim,

Happy to have helped, it took me over a year to sort my issue out, at least I can visualise the entire engine oil system with my eyes closed now !
Malc Gilliver

This thread was discussed between 28/05/2025 and 12/07/2025

MG Midget and Sprite Technical index

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