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low oil pressure

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johnjoan6203

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just finished with major rebuild on 1973 MGB, new pistons 020, main and rod .010, new oil pump and strainer ,new oil pressure relief valve, new cam and bearings,double row timing gears and chain, now for the head all new valves, guides, springs, seats, new push rods , new lifters , new pressure plate, clutch, release bearing, only have about 50 miles on this rebuild ,oil pressure is low at idle between 15-25 psi.when warm going down the road its about 65-75psi at 3000 rpms,Is this normal /ubbthreads/images/graemlins/confused.gif
 
What does your manual say?
 
Sounds good to me. That's where it should be. You're "good to go." /ubbthreads/images/graemlins/wink.gif
 
That idle oil pressure is much too low for a fresh engine. Did you check the rod and main clearances? One common mistake is to mount the oil pump with the wrong gasket. Two gaskets typically come in the gasket set but I don't know why. The larger one is correct for the 5-main engine. And of all the engines I've seen with this problem , they all seem to act differently. Some will not pump oil at all and others have good running pressure and lousy idle pressure. The giveaway was the air bubbles coming from the rocker shaft.

Alan T
 
/ubbthreads/images/graemlins/iagree.gif Oil pump gasket is the first thing I'd check - that idling oil pressure should be higher...also, there's a tiny hole in the edge of your rods down by where the caps attach - its used for wetting down the cylinder walls by oil squirting out it - which direction did you point it when you reattached them to the crank, towards the oil pump side of engine or away?
 
I remember from discussions on other forums if a 3main gasket is used on a 5main the oil pressure would be zero because the 3main gasket covers a hole used by 5main pump. A lighter than recommended oil 20w/50 in new rebuild when running warn/hot will produce lower idle pressure.
 
<runs out to warm up the MG> Now I'm compelled to check mine at idle when it's at operating temp...
 
The 3-main gasket does not cover an orifice . It leaves an air gap the gasket thickness in the pickup side. I've seen this over the years about five times. Sometimes they will not pick up oil at all. The best foul up by a novice engine builder in this department is the one that made a gasket for the machine fit oil pump body to pick up casting and wondered why it would not pump oil.

Alan T
 
checked the owners manual& hayes book and they both say 10-25psi is normalat idle.well I'm going to change to a heavier oil 20w 50 thanks again!
 
There ya go, spot on. Nice.
 
Before doing anything, make sure your oil pressure gauge is accurate. Get a handheld oil pressure kit and attach it directly to the engine block. If you are running a thinner oil than 20W-50, I'd recommend changing. Castrol GTX is the most common type for these cars.
 
Well, with GTX 20-50 and at normal operating temp, my idle pressure is 25~30, and upon revving it up to 3K the pressure goes to around 70~75 PSI (80 when cold). I assembled this one "tight" (close end of the tolerances) and expect a ~slight~ decrease as it goes through its life.
 
What the heck is a handheld oil pressure kit?
 
An oil pressure gauge on a rubber hose with a threaded attachment at the end. You unscrew the oil pressure unit form the block and thread the oil pressure gauge into it. Start the engine and see what the gauge reads.
 
Ha, ok, I asked for that I guess.
 
Now that I re-read my original post, I see that it was worded strangely. Sorry! /ubbthreads/images/graemlins/smile.gif

Something like THIS.
 
Ahh, okies, understand that link for sure.
 
If you are idling at 400 you will have low pressure, of course.
the first question should be: At what idle RPM are you getting what pressure?

Guinn
 
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