Oil (not) Pressure

[silloyd]

Hi all,

I'm struggling to get oil pressure after the car has sat for a long time (>2 years). I just can't any significant reading on the pressure gauge and the oil light will not go off

If I prime via the plug on the exhaust side of the engine and turn the engine manually then oil successfully pumps through to the oil pressure switch hole, oil take off pipe hole, and spin on oil filter bracket, so the pump is working in that context.

After priming, when I spin the engine on the starter motor (with plugs out and priming plug fully tightened) the pressure will not raise!

Other info: I've had the sump off to check the pickup and its clear and sealed to the block. Oil filter is new and full of oil. Pressure relief valve spring is the correct length (according to the manual) and therefore, as far as I know, oil is not dumping direct to the sump. Oil level in sump is correct. Battery is charged and spins the engine well. Engine was rebuilt about 500 miles ago with a new oil pump.

I'm losing the will to live trying to get pressure. Anyone got any useful suggestions please!!

[svenedin]

My oil light doesn’t go out until the engine has actually started. Spinning the engine over on the starter is not enough.

Stephen

[geoberni]

Anyone got any useful suggestions please!!

Stop messing around, put the plugs back in and start the ruddy thing!

I'm with Stephen, why on earth do you think that spinning it over on the Starter will make the Oil Light go out?

(IMHO)
The Starter doesn't turn it over anywhere near fast enough...
The Starter turns it at perhaps 150-200 rpm at best, while at idle the engine is doing about 800-850rpm....
.
.
.

Edited to add the IMHO, to keep it in context with my later comment 10:35 1/10/24

[silloyd]

...why on earth do you think that spinning it over on the Starter will make the Oil Light go out?

This post clearly recommends building oil pressure before starting the engine; I'd rather not risk the bearings by putting it under load without being sure the oil is where it needs to be.

[philthehill]

You are quite right to get the oil pressure up before starting the engine.
Whenever I start my engine I always firstly take out the plugs, prime the oil pump and then spin the engine over on the starter to get the oil pressure up. Remember to spin the engine long enough to get the oil around the engine. Then I will refit the plugs and start the engine as normal. I can get max oil pressure by spinning the engine on the starter motor.
I would not do it any other way.

[silloyd]

... firstly take out the plugs, prime the oil pump and then spin the engine over on the starter to get the oil pressure up. Remember to spin the engine long enough to get the oil around the engine.

Thanks, I tried that (please see first post). I'm not sure how long is "long enough" but I'm not getting pressure after about 60 secs, which seems a long time on the starter motor, hence the ask.

[geoberni]

...why on earth do you think that spinning it over on the Starter will make the Oil Light go out?

This post clearly recommends building oil pressure before starting the engine; I'd rather not risk the bearings by putting it under load without being sure the oil is where it needs to be.

And right at the end of that Topic it says: viewtopic.php?p=602273#p602273

I will bow to Phill's experience, but I still think it's asking a lot of a Starter motor to get sufficient pressure. Yes it will turn the engine over and prime it,but as to turning the lamp off..

[philthehill]

Go right back to basics and check that you have or have not got oil pressure with a oil pressure gauge.
If you have not got a gauge and you have a spare oil pressure switch change the oil pressure switch.
Try the process again and see if you can get oil pressure.
It is not unknown for the oil pressure switch to fail which would result in the oil pressure warning light staying on.
Be aware that some later oil pumps with the rotor pressed onto the drive shaft and with no other means of retention have been known to have the rotor come lose on the shaft resulting in oil pump failure and no oil pressure.
Unfortunately a major job to rectify.

[silloyd]

Thanks for the suggestions philthehill.

I have a Smiths pressure gauge fitted as well as the switch but it shows no meaningful pressure rise and the oil pressure light stays on. Oil is flowing to the pressure switch port when I manually crank, so no blockages.

I've tried the process several times and each time the needle on the gauge lifts slightly but it's minimal, i.e. ~5 psi indicated. Occasionally the oil light will flick off for a second but it won't stay off. Unless both have failed, I'm not getting meaningful pressure.

Oil pump was new at rebuild c.500 miles ago (It's a slot drive pump because an MG Metro cam is fitted). As per earlier post, if I manually crank whilst adding oil to the priming hole then I get oil flow right through to the oil filter. Only thing I can think of at present is that there is sufficient connection/friction between the pump shaft and rotor for it to work at at low speed but insufficient to run the pump properly at higher cranking speeds. Ill try cranking on the starter with the pressure switch out to see if I get any flow - could get messy!

Not relishing the thought of taking the engine out to replace the pump!

[mowogg]

I would agree you should have oil pressure turning over on the starter. I always turn mine over on oil change to reach 50psi before starting.

Not sure if this would be the issue, but could the oil pressure relief valve be stuck open?

[liammonty]

I would agree you should have oil pressure turning over on the starter. I always turn mine over on oil change to reach 50psi before starting.

Not sure if this would be the issue, but could the oil pressure relief valve be stuck open?

Agreed - an engine in good health should achieve enough pressure to put the light out turning over on the starter, and mine (rebuilt 14 years ago) can achieve at least 50psi on the gauge on the starter when cold (I always spin it over on the starter with the ignition off after I've done an oil change to build the pressure up). If the engine in question was recently rebuilt before being laid up, a stuck pressure relief valve could be a possibility if there was a bit of swarf left in the galleries somewhere?

[geoberni]

So having no experience of trying to get the oil light out on the Starter, I went out and tried it this morning....
Every day's a School Day and such...

The engine was last turned over yesterday.
So with the Coil disconnected, I cranked it over, ...and over, ....and over.... and at 21 seconds the light went out.
I've never cranked it so long while deliberately watching the green light.
Just for context, on a normal start, it goes out about 2 seconds after it fires up.
Bearing in mind that the Oil Pressure Switch is 8 psi, and Idle Speed is supposed to give about 20psi, so 21 seconds of negligable oil flow.

So I've learnt something today, but I'm not sure it's something I'd want to repeat too often...

I would agree you should have oil pressure turning over on the starter. I always turn mine over on oil change to reach 50psi before starting.

That seems excessive on an oil change.
The engine surfaces are already coated in oil from having been running before the oil change.
Nothing has changed in that regard, it's not like starting up a dry, newly built engine, or one that has been stood for months/years...

[myoldjalopy]

Ess, as long as the filter canister has been 3/4 filled with oil, I can't see it really necessary to turn the engine over before firing up after an oil change. At most, one might turn the engine over on the handle a few times, but each to their own - turning over on the starter before firing up certainly can't do any harm.
As for newly built engines, received wisdom is to crank the engine on the starter until the oil light goes out and to continue for a further 15 seconds or so - and only then to actually fire up.

[silloyd]

So, I:

• stripped out the pressure relief valve, nothing obviously untoward but cleaned it anyway and reassembled;
• Removed the pressure switch and pressure gauge adapter, again nothing amiss, so reassembled minus the pressure switch and primed until oil coming out the hole, then reinstalled the switch;
• removed the oil pickup pipe banjo and primed to make sure oil was flowing, again fine, so reassembled;
• cranked on the starter motor and this time the light went off for a few seconds and the gauge showed ~15-18 psi;
• based on the pressure being close to idle minimum, I decided to start the engine and .... pressure instantly leapt to 55psi and stayed there!

In short, not sure why I couldn't get decent oil pressure on the starter motor but maybe it's not spinning as fast as it should IDK!

Top bonus was that the engine fired first time after that extensive 2+ year rest up. Note to self: make sure you fire up the engine periodically to maintain the oil flow / pressure!

Anyhow, thanks for the help all.

[geoberni]

Well, like you say, perhaps it's not spinning so fast; especially as it's low on running time after rebuild and you've been playing with it a while and perhaps not charging the battery in between tries.

Glad you've got it sorted.

[alanworland]

My Series MM doesn't get a lot of use but I will from time to time spin the engine on the starter by pushing the starter switch directly it will spin for 'say 10/15 seconds' when I can hear the starter motor comes under more load as oil is being pumped.
This will give well over mid gauge, 40 psi.
Generally when starting the engine I have always spun it with the starter before turning the ignition on.

Alan

[geoberni]

This has been an interesting topic, especially regarding those who regularly 'dry spin' before starting their engines.

Whether this is beneficial for an in-use A Series, rather than a newly rebuilt one, is clearly a matter of personal choice.
Personally, I prefer to get it running, and would only spin it over if left for a considerable time.

However, on the same subject, back in the early/mid 1990s, I did some volunteer work on Catalina G-BLSC (the one that sadly sank in the Solent around 1998 after a nose gear door failure on landing).

One of the jobs was relating to pre-oiler pumps.
When originally constructed, lifespan of engines was not a question, or expectation, but as these and other surplus aircraft and engines entered the civil market post WWII, operators had concerns about excessive wear from cranking these large rotary engines over to get the oil circulating, pre starting.
This lead to a common modification to install pre-oiler pumps. Run an electrical pump for 20-30 seconds to lubricate the cylinders before starting.

Anyone fancy do that to their Minor?
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G-BLSC.JPG (28.57 KiB) Viewed 1198 times

[philthehill]

Kits are already available for pre-oiling the engine.

https://www.merlinmotorsport.co.uk/file ... ctions.pdf

[svenedin]

On Minors with key start it is not really practical to spin the engine over without the ignition or fuel pump on before starting on a routine basis. The bonnet would need to be lifted and it would be possible to spin the engine over on the solenoid button without the ignition on assuming the original type solenoid is still there (later square solenoids lack the button).

As an alternative, some owners with key start spin the cold engine over on the key with the choke fully in so that the engine will not start and then whilst still spinning on the starter pull out the choke so that the engine will fire. That strikes me as quite a good idea.

Stephen

[myoldjalopy]

Or, if no easier method is available (pull-starter or solenoid button), just remove one of the wires from the coil......