oil pressure

Topics related to the engines for the later MG Midget series.

oil pressure

Postby Georgia Cracker » Sun Feb 12, 2006 8:34 am

I recently acquired a '76 Midget with 26,000 miles. Mechanically very sound, maybe the tightest MG I've ever driven. The oil pressure is 75lbs when first cranked up, but as it warms up it drops to 45lbs. at speed and 10 lbs at idle. I thought it might be the thrust bearings dropped out, so I pulled the oil pan and replace the rod bearings, main bearing, and thrust washers. I've alway heard that low oil pressure after warming up is usually cause by worn main bearings. Well, it made no difference at all. I removed the oil pressure relief valve, the valve looks ok, the spring is just a hair under the proper length so I put a couple of shims under it. That jacks up the oil pressure 5lbs when first cranked up, but then it drops right back to where it was when warm. What's up with this engine? Can it be the oil pump? Is it because the cam has no bearings and has worn the block? I'm used to the 1275, and I know the peculiarities of them, but not this engine. Please note that I did not plastigauge the crank when replacing the bearings, I figured that at 26,000 miles it should not be that bad. Also I am running 20W50 oil as per the manual. I know I can put straight 40W in and jack up the pressure a bit, but that is a temporary fix.
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Postby Frogarri » Sun Feb 12, 2006 2:53 pm

Another thing to check would be the rocker arm shaft. After it warms up does the oil flow to the rockers increase? With only 26,000 it should not be worn but if old parts were reused there could be some slop that when warm lets too much oil flow and hence the drop in pressure.
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Postby Acmespeedshop » Sun Feb 12, 2006 5:46 pm

If you ever rebuild this engine and want to have cam bearings, there is a rather easy fix. The 1500 block will accept the 1296 cam bearings in the 1500 block without modification and then you run a 1296 cam and you now have cam bearings. Just a little tip I though you may want to know for future reference
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Postby Georgia Cracker » Mon Feb 13, 2006 6:34 am

Thanks for the replies so far. Please note that I did not do a full rebuild of the engine, just a bearing change with the engine in the car. I am curious, is a sloppy valve train typical of these engines? Or worn cam bearings? I had heard you can put the earlier style cam bearings in, but is that a typical cause of low oil pressure in this engine? Do the oil pumps wear prematurely causing this problem? I know what 1275's do, but I have no experience at all with the Triumph engine. What should I expect?
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Postby Georgia Cracker » Sun Mar 05, 2006 10:12 am

Well, I answered my own question. Yesterday I went ahead and dropped the oil pan again and pulled the oil pump. Sure enough, it was right at the limit of acceptable spec. So I drove over to Atlanta Imported (great guys, lots of knowledge), and picked up a new pump. Now the oil pressure after warming up is 20+ at idle and 60+ at speed, about where it should be. So I would recommend to anyone replacing the rod and main bearings to go ahead and replace the oil pump while you have the pan off. For $85 it's cheap insurance.
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