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MG Midget and Sprite Technical - Pressure relief valve working?

I had the pressure relief valve off a few weeks ago to have a look. (I know, I can't help it). Engine pressure seems fine but how do I know the valve is working and not just leaking or causing high pressure by not working properly? (that must be possible?)

Was reading the archive over the weekend and someone mentioned changing the valve for a different type as they reckoned the original was not reliable.

Any experiences / comments appreciated.
Dave Squire (1500)

Dave. The most common method of determining whether the engine is operating at the proper pressure is to look at the dash gauge. If it is showing the proper pressure, or range of pressures, that are listed in the Driver's Handbook and the factory Workshop manual, the pressure relief valve is considered to be working properly. The oil pressure (at least on the BMC engines) was taken after the relief valve and were an accurate indication of what was happening. But, I am not familiar with the 1500 engine and do not know if they used some different take off point. But, if so, it would be the only engine I know of that did so. If the gauge is reading good, everything should be working fine. If the gauge is not reading good pressure, cross test with a second gauge before stripping down the engine.

Les
Les Bengtson

Hi Les, the 1500 1978 triumph engine doesn't have a gauge, just a light by the ignition light on the speedo. I suppose I will have to sort out a gauge if I want to know more of what's happening. Being on here just kicks me back to reality from time to time.

Thanks.
Dave Squire (1500)

Dave. Thanks for adding to my knowledge of the last midgets. The Sprite I had did have a pressure gauge on the dash as do my current MGBs. Yes, I would definitely hook up a gauge and see what is happening. It provides you with a world of information that a light cannot. Good luck.

Les
Les Bengtson

and of course it adds a world of worry if you read too much into what it shows,

however I do think, allowing for a gauge is just a gauge and the variances of different engines at different ages, that an oil pressure gauge would be useful

but don't consider an oil temp gauge, especially with an oil cooler fitted to a UK road car, or you'll be relly worried
Nigel Atkins

and of course it can add a world of worry if you read too much into what it shows,

however I do think, allowing for a gauge is just a gauge and the variances of different engines at different ages, that an oil pressure gauge would be useful

but don't consider an oil temp gauge, especially with an oil cooler fitted to a UK road car, or you'll be relly worried
Nigel Atkins

Dave - I think I mentioned elsewhere recently that I added an aftermarket oil pressure gauge to my '78. I installed a T-fitting at the sensor port, screwed the pressure switch into one side of the T, and ran a capillary tube from the other side through the bulkhead to the gauge, which I mounted to the bottom of the dash. It works just fine, and provides a dual reference in the gauge plus the light.

My reasoning is that when you see the light come on, it's already too late... and the gauge will show any trend toward lower pressures, giving you forewarning if your engine's developing problems.

I used to have pictures posted, but those went away when I let my web space expire. Sorry -

Cheers,

-:G:-
Gryf Ketcherside

Dave, x2 for fitting a gauge then you will know a whole lot more and as Nigel says a "world of worry" interpreting the results! Alternatively ignorance is bliss :0)
Back to the valve...
As you probably noticed it's a simple affair and as long as the face of the plunger is flat with no wear ridge and it’s free to move in the spring, all should be well. The spring sets the relief pressure and uprated ones are available but I think a standard one for road use is more than adequate. The spring is a fairly substantial unit for the work it does and I’m not aware of any issues caused by the spring ageing and going weak but guess it is possible.

Best of....
MGmike
M McAndrew

Thanks guys, I am convinced about the gauge and will fit one, in fact, now thinking about it, I may have one from the older car that's in bits.

The present problem is I have a lot of oil on the bottom and back of the engine which I am fixing. It is getting less as I work my way down the engine. The top half of the engine is now dry at last. However I noticed a bit of a slick from the relief valve so wondered how it worked. As Mike says it is simple. On further reading I understand it should be sealed and not open to the outside. The pressure relieves internally to the sump. I therefore should not have a slick of old oil from it on the outside and on closer inspection found the copper sealing washer to be missing.

This car is missing all those bits and pieces that cause hassle and don't cost a lot like ...... MG Badge Clips and ..... Head Gaskets. Lol :-)

Anyway, thanks for your help, much appreciated, Cheers, Dave
Dave Squire (1500)

Dave,
I was going to put did you change the copper washer when you took the relief valve out - I'm almost sure on previous links given it says to renew washer

try to be helpful now - I really think it'd pay you to get that DVD as it has the factory Workshop Manual that would help you see what goes with what and where as would the factory Parts Catalogue that's also on there (plus of course the good books)

I missed or forgot this engine was one that had been sitting around for a good time before you put it in the car without doing any/much(?) work on it before or after installation - I wonder if this is a case of doing a compression test on it if you've not already done so to gauge what sort of condition it's in, I didn't realise until recently that it'd been sitting with rusty water in it(?)

I assume (don't know) it's still a good idea to check the engine breather pipes are clear and clean and not dripping with oil inside
Nigel Atkins

I'll join Nigel in putting in a plug for the Factory Manual. Once I bought a copy of my own, I gave away my Haynes... if nothing else, the factory book covers the 1500 specifically, so there's no flipping past irrelevant chapters trying to find what you want.

Cheers,

-:G:-
Gryf Ketcherside

Should be a minimum free length of spring. Did you pull out and measure? Check workshop manual for spec, i dont have mine on me. If else, just replace it (they're cheap).
Ron Koenig

According to Bentley manual:
Oil Pressure relief valve spring free length 1.53" (38.8mm)
Ron Koenig

This thread was discussed between 24/04/2013 and 29/04/2013

MG Midget and Sprite Technical index

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