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MG Midget and Sprite Technical - Oil pressure too high

After a protracted year long sulk, I have gone back to my garage to finish an engine swap and five speed upgrade.
I've got to the point where I'm almost ready to fire it up for the first time, so I removed the plugs, disabled the ignition and fuel pump, and turned over the engine to circulate some oil and check for pressure.
The pressure came up after a couple of bursts on the fancy new starter, but as I churned it over the gauge continued to climb until it was full scale. The reading dropped back to zero when I switched off.
I'm not really sure where to start checking for problems.
I haven't changed the gauge, which was working before I removed the old motor. The feed is new.
The new block has been chemically and mechanically cleaned.
I renewed the oil pressure relief valve seat and replaced the plunger with a ball bearing and spring.
The oil filter housing is now an MED type with a flexible transfer pipe.
There's no oil cooler.
I renewed the oil pump.
I checked each gasket for alignment as parts were added.
The motor turns over ok. I checked for tightness at various stages of the build.
I'm using Halfords cheap 20w50 for running in.
I used engine building paste for assembling the moving parts, but the motor has sat in the workshop for a year since I finished it's build.

Do you think that the most likely problem is a sticking O/P/R valve?
Would that allow the pressure to build up just on the starter?
I'm sure the OPR valve seat was 'seated' ok, the sound was right when it bottomed in the block.
I bought a spring and ball bearing as a pair from a Mini spares place, could that be wrong?
What other horrible thing might I have done wrong?
I really can't face taking the motor out again after the performance I had with getting the clutch to work.

Mark, despondent in Preston
M Crossley

When I've used a ball bearing in the OPR valve, I've had to shorten the spring to get the pressure down to 'normal'.

If I was going to build another engine, I would just use the standard valve.
Dave O'Neill 2

It has to be the relief valve
It would be highly unlikely that the ball would stick shut so I would think that the spring is probably incorrect for your application (too strong)
If I remember correctly Prop had this problem and refitted his original spring but retained the ball
I'm sure he'll respond shortly

Too much oil pressure can be fixed. it's when you have none you are allowed to get despondent - stick with it you're nearly there.

cheers willy
William Revit

I bought a spring and ball bearing as a pair from a Mini spares place, could that be wrong?

Yepp... I had that problem, I got the spring ball bearing and adjustable cap and the spring was to long...i didnt have any issues with oil pressure before the build, so I used the old spring and new cap and ball bearing with no issues...

I think I got my spring ball and cap from minimania which is a sister company to mini spares so they may use the same supplier for that part

Prop and the Blackhole Midget

Don't forget cold pressure new engine new oil will be extra high.
If worried start engine then drop spring length till you get required psi.
problem we had years ago and still obtains is we cannot buy quality oe style relief valves which were steel, copper plated then hard chrome plated, all we find is plain steel. These have poor wear properties and is even more prone to sticking so we only fit ball bearings.

Peter Burgess Tuning

Thanks for the info chaps. I'm not an engine builder, I just read instructions and bolt stuff together. So when things don't go to plan, I'm the first thing that I suspect.
My clutch problem turned out to be a cheap, ebay concentric slave cylinder, but it took me four or five engine remove/replaces before I'd sussed it out.
My vision of ripping the engine to bits again has receeded a bit!
I'll have a quick look at the spring to reassure myself. and then worry about it once I've fired up the motor.

Thanks for your help.
M Crossley

Mark, noticed your comment re problems with Concentric Slave. I have thread "More 5 speed woes... The Saga Continues" running which is basically my problem with a Concentric Slave. Can you have a read and maybe post some comments?

Rob aka MG Moneypit

Hi Rob,

I've been following your thread, although I haven't posted. For one thing, I've only really done what others like Guy, Lawrence and JLH have already suggested. For another, I still haven't tried the clutch in anger. I haven't had a running engine, so I can only go by the way the pedal feels.

I worked out dimensions to suit my parts. The flywheel is a lightened MED one with their pressure plate and an AP Racing 7.5" friction plate. The release bearing runs directly on the pressure plate fingers. I used a 19mm spacer from Burtons. This size would give just about 0.1mm interferance if there was literally no friction plate, and about 5mm with a new plate.
See a thread "Concentric Clutch Release"

I bought two different spigot bearings from the Morris Monor Centre. Neither suited my input shaft. I pressed out the oilite bush and made a new one. I bought the input hose from Venhill. They make up lines to your request. The output/bleed hose I settled on was from Burton. Its a bit long, but I struggled to find the right fitting elsewhere.

My main problem so far was in actually keeping fluid in the system. I bought a Burton-style concentric off ebay. Brand new and boxed with a Burton part number.
After several attempts (engine in & out) at sealing the hoses within the bellhousing I finally discovered, by mocking up the system out of the car, that the threads for the plumbing weren't perpendicular with the counterbored faces that the copper sealing washers butted up against.
Once I bought a new cylinder from Burton it worked first time.
See a thread "Hydraulic Hose Seals for Dummies"

So, as you can see I'm not far enough ahead to have useful info to contribute. All I know is that there hasn't been a puddle of hydraulic fluid on the floor for the last 6 months that i've been sulking and motorcycling.
My intention, once the cars up and running, is to fit an adjustable limit stop to the pedal. I seem to remember my old Alfa had one.

Hope this gibberish helps.

M Crossley


Id go ahead it up and see what happens...ive never heard of one of these engines blowing up from to much oil pressure....its fairly common for people to report 80psi at 4000 rpm

What was your oil pressure off of the starter ?

Peter makes a great point...

""Don't forget cold pressure new engine new oil will be extra high""

Prop and the Blackhole Midget

Also, as the engine had been idle for so long maybe the ball is stuck to the seat?

Rob aka MG Moneypit

Rob, Prop,
Both good points, although the gauge rapidly went to full scale. I can't remember exactly what that is, but it's a standard capillary o/press & w/temp gauge. I think 150-ish psi. I'll check on the scaling.
If the OPR ball was stuck to the seat, would that produce that sort of symptom?
What other fault or assembly error could result in 150psi on the starter?

M Crossley

>>> What other fault or assembly error could result in 150psi on the starter?

Many many years ago I can remember having a similar problem on a mini I had, though I don't remember whether it occurred on the temp gauge or oil gauge - but only on trying to start. The problem was that the pipe to the gauge was acting as an earth to the engine, so when the starter was cranking the pipe got very hot and the gauge would shoot up!

J Smith

One other option but I cant remember if it makes a high or low oil pressure is using allen screws instead of caps in the oil galleys ...if you use an allen screw thats way to long it gives some issues

Google keith culvert, he has a good write up artical on maybe an old artical and hard to find, poor keith fell off the face of the world map when his daughter was murdered several years back....but his wisdom and words still live on in cyber space.

Prop and the Blackhole Midget
J Bubela

Thank you J.

I had no idea that site existed

Prop and the Blackhole Midget

This thread was discussed between 03/03/2015 and 05/03/2015

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