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MG Midget and Sprite Technical - Oil Pressure Relief Valve

Hi all,

I've had intermittent problems with oil pressure over the last few years on my 79 midget 1500 (stage III, oil cooler, external rocker feed, cam bearings).

When all working correctly the oil pressure will be normal i.e. with hot idling around 15-20psi and picking up quickly to around 40-50psi around 2000-2500 revs.

When the problems begin the oil pressure at idle drops to around 10 psi hot but more importantly does not quickly pick up as the revs rise i.e. only being around 20-25psi by around 2000-2500 revs. This means that with normal road (e.g. 30mph) driving in top the oil pressure is only around 20-25psi.

The usual resolution for this has been a new oil pump but I can't believe it should be destroying oil pumps every 5-10 thousand miles? When the problem occurs it does so suddenly from one drive to the next. Could it more likely be related to the oil pressure relief valve? I've taken it out and cleaned it on a couple of occassions but this doesn't seem to have made much difference. Does the seating area inside the block need to be cleaned? If so what's the best method for this? Don't want to damage anything internally!

I've attached a picture of the relief valve, does it look ok?

Thanks.
Rob.




ra hollingsworth

Hello Rob,
Your relief valve looks worn on the seat. However, I wouldn't expect this to be the whole reason for experiencing the symptoms you describe, as it would be constant and not cause the intermitent low pressure every few thousand miles. Possibly you have some debris down on the mating seat that moves around a bit so that sometimes you get a good seat and sometimes you dont. This would cause the wear that can be seen on the plunger seat. Try cleaning it with a cotton bud or similar, with some grease on. This will stop any lint becoming detached, and will "glue" and dirt to the end without leaving anything damaging in the valve. Then by turning the engine on the starter motor for a second with the valve plunger removed, any muck down the feed to the pressure relief valve will be blown out with a squirt of oil.

A new valve and spring costs peanuts so it would be worth fitting one. Moss recommend fitting an uprated valve spring if using an oil cooler as well.





Ben Whiteley

Have a look at an adjustable one about 15.00 from mini-spares.
Brad
B Richards

This thread was discussed on 09/09/2008

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