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MG MGB Technical - 72 B Engine Diagnostic Help

Hello all:
I am a regular on the TD Board. I have a question for all you "B" Experts. I have a friend who was out driving his 72 B at speed on the interstate and having a nice time, no problems, when he says he heard a "disturbing" noise which he believes originated from the engine. He says he also noticed a loss of oil pressure, and immediately put it to the side of the road and had it flat-bedded back home. He would like for me to take a look see at what could be the problem. Sorry I don't have more info at this time, however, could you give me a starting point? Oil pump/shaft, spun rod bearing?
Thanks to all for any help.

Brian Warmuth
Wheeling, WV USA
ZBMan

Brian,
TD, I wish! Or is that dream...
Not a lot of info to help with the B. When you do get there start with the basics.
Try a cold start and if you don't see 75psi oil pressure (which I think is the relief spring setting) switch off, strip and renew the bottom end eg pump, bearings, relief valve and spring etc.
If that's okay, let us know what you find and we'll comment.

MGmike
M McAndrew

try doing a compression check first. the same thing happened to my 72 b-gt and i found a blown head gasket and also #2 piston broken at the ring grooves. in process of doing a complete overhaul right now. good luck
RP Padilla

Get him to drop the sump. will take 20mins and give you sure indication of the problem if it's catastrophic. Metal in the sump and loose big ends are indicative of bearing problems. Can also check things like the pressure releif valve and the oil pump. If you undo the front mounts you can jack the engine up a tad and get to the front sump bolts.
A J Ogilvie

Thank you all:
First I will start with a fresh battery. Check the oil level in the sump. Then I will take out the plugs/disable the ignition. I will take a compression check on each cyl, whilst listening for "bad" noises and also check to see if I pump up oil pressure. If no pressure, I'll take the oil line off and also check the relief valve seating. With the line off, I'll crank to see if I'm getting any oil out of the pump. If so, I'll suspect the gauge or sender. If no oil, off comes the sump. Sound good?

Brian Warmuth
ZBMan

Sounds like a plan to me, Brian.

My GT, which is a little earlier, has a rather expensive sending unit for the oil pressure gauge. I'm not sure if it is used on the 72, but take a mechanical gauge with you if you have one.

Charley
C R Huff

O.K. so here's an update. Early 5 main engine. Had to pull the pan. #4 rod bearing trashed. Crank journal may be alright though. No oil pressure though the gauge does work when tested. Oil supply line when disconnected - no oil out when engine cranked. Pulled oil pump/shaft- seems to be perfect.

What gives with the oil pressure? If the relief valve were stuck open would this cause ALL the oil to dump back into the sump without pressure oiling #4? etc.?

I suppose I should check the pressure relief valve - it's a pig to get to isn't it?

Thanks for all help.

Brian
ZBMan

Brian, if the releif valve is stuck open it will dump a lot of oil back to the sump but with cold oil I would expect some pressure to build. It's a bit of a challenge to get to! It's on the carb/exhaust side of the engine down the bottom at the back of the block! It's well hidden by the exhaust down pipes. If you can get the cover off you might just want to try a thin punch to tap it back on to the seat. Otherwise you are looking at an engine out to get proper access.
Which oil supply line have you disconnected?
If the pump's working and you spin the engine long enough you should get something (but I guess you know that!). It sounds like you may have a blockage somewhere.
good luck finding the problem.

MGmike
M McAndrew

Some bits of the bearing may have gotten under the sealing surface of the relief valve causing it to dump all of the oil back into the sump. Match mark the cap of the relief valve with the engine block just as the threads begin to align, with the spring removed. This way, the threads will start much easier upon re-installation of the cap. RAY
rjm RAY

I'm going to look at it again tomorrow. Will report back with more info as available. Thank you all for your help and suggestions...it will save me some time. If the rod journal on the crank is not bad could I just install new rod bearings without taking the engine out? What is the wisdom on that? Of course, I first have to figure out the absence of oil pressure. I have the pump out, cleaned, and it looks very good no issues I can see with it.

Brian
ZBMan

Brian,
the only way to be sure the journal is okay will be by measuring with a micrometer. That being said, a bearing is a lot cheaper than a strip and grind... If you find and fix the cause of the problem, try a bearing if only to see how it copes over the summer. You can always strip it if it starts to knock and it will only cost you a few $'s. Check the pump clearances before putting it back. You want to aim for .002 lobe clearance and less than .005" clearance between the moving parts and the body of the pump (but I don't really see the pump as the problem).

BTW which oil line did you disconnect?

Mike

M McAndrew

Mike:
I disconnected the flex line going from the block.

Brian
ZBMan

This thread was discussed between 19/04/2011 and 27/04/2011

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