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MG MGA - engine life

The motor was reconditioned seven years thirty thousand miles ago.Long story short did compression test 1&2 cylinders 100 psi 3&4 0 psi.No oil in water or visa versa. Just having a rant BW
Bob Walker

That's a little unusual, indicating a blown head gasket between #3 & #4. The more common blow-out point is between #2 & #3. At the very least the head has to come off. Before you do that, how is the oil pressure when running (if it can run on two cylinders). Oil pressure at idle speed with hot oil is a good indication of crankshaft bearing condition.

Probably not much use trying to do a blow=down test on #1 & #2 to determine where those are leaking. Once the head is off you can invert it and pour some mineral spirits into each chamber to see if the valves leak. Also turn the crankshaft until all pistons are at half stroke, then pour a couple ounces of mineral spirits into each cylinder, and see how long it takes to leak past the rings into the crankcase. If it leaks down in a couple of minutes the rings are either stuck or worn out, and in either case the pistons have to come out for new rings (or worse).

You can also use a dial bore gauge to measure cylinder bores, up, down and sideways so to speak. If the bores are correct size and cylindrical within 0.003 inch, maybe you get by installing new piston rings. If the bores are shot, then the engine comes our for complete disassembly and machining.

Pulling the pistons gives you a good look at the connecting rod bearings and con-rod journals on the crankshaft. When the pan is off it is easy enough to R&R the enter main bearing car for inspection of the bearing. Front and rear main caps are a little trickier to R&R in situ, but can be done. If crank journals are okay you can install new bearings. If the crankshaft needs to be re-ground, the engine has to come out for disassembly.
Barney Gaylord

Thanks for reply Barney. I ran engine till 160F (it didnt like to idle for long)oil pressure 40 psi at idle. Is there any chance of this being a head & gasket only problem? BW
Bob Walker

Superficially it sounds like an old and tired engine, but may have more years to run yet. A new head gasket should get it firing on all 4 and running "okay" but not great. Low compression on #1 & #2 may be equaled by #3 & #4, figuring it has tired rings or leaky valves (usually exhaust valves).

40 psi oil pressure at idle with cold oil sounds like somewhat worn connecting rod bearings, but it depends on how slow it was idling. If you get it running decent with a new head gasket, and oil pressure is still a little low, then it's easy enough (sort of) to R&R the oil pan to replace con-rod bearings (which usually does a world of good to increase oil pressure and prolong engine life).

In any case, minimally, the head has to come off to change the head gasket. While the head is off do the mineral spirits test to see how badly the rings and valves are leaking. If you have leaky valves you might R&R the valve springs and hand lap the valves, hoping they are not too badly worn and recessed into the seats. Before we get any further into speculation, pull the head and let us know what you find.
Barney Gaylord

40 psi was with heated oil,it was 65 psi at startup idle. I will work on this on weekend and update. BW
Bob Walker

#1&2 on head both have leaky exhaust valves #3&4 seem ok.Cylinder bores ok rings held fluid for 12 to 15 minutes

Bob Walker

Time to hand lap the #1 & #2 exhaust valves. Before you put it back together with a new head gasket, use a straight edge and bright light to check both surfaces for flatness between #3 & #4 cylinders.
Barney Gaylord

thanks Barney Bob
Bob Walker

Running again no water in oil/visaversa. only went about 5 miles
Bob Walker

This thread was discussed between 02/05/2013 and 05/05/2013

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