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What, exactly, causes MGB oil leaks?

Posted by Kent -In-KC 
Kent -In-KC Avatar
Kent Hartland
Kansas City, MO, USA   usa
1977 MG MGB

Me again. FNG. Another question that's probably been asked a jillion times.

If I hoist the engine/tranny on my nearly-purchased '77 MGB and replace pan, valve cover, etc. gaskets can I effectively eliminate most oil leaks? I realize that doesn't account for a bad main seal or some likewise major problem.

Is it really true that you just have to accept oil leaks with a LBC? Do modern neoprene gaskets, permatex, etc. make a difference?

Thanks, all.

Clay Johnston
Mt. Olive, MS, USA   usa
1972 MG MGB

Putting any kind of fluid in/on the car smiling smiley

Just kidding. A common leak point is the tappet covers on the side of the engine. Front timing cover and seal are easy to replace as well. IF your pulling the engine, might as well check the rod bearings and mains, replace the oil-pan gasket while your in there.

Have you done a compresison-check? Easy diagnostic tool.

Oil leaks can be exacerbated by blow-by due to worn rings or improper crank-case ventilation (top or bottom).





Edited 1 time(s). Last edit at 2009-03-28 11:02 AM by ClayJ.

P P
O, Ontario, Canada   can
1967 MG MGB GT "Maggie (GT From Hell)"

What Clay said. Im not kidding!

Pete

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78mgb Avatar
White Wonder 78mgb
apple valley, Minnesota, USA   usa
1978 MG MGB

Fixing the side cover leak is the hardest one. I tried rubber gaskets and modern gasket sealers but they would start leaking again. I was at a NAPA store and asked for some gasket sealter. He gave me some Indian Head Gasket Shellac Compound Item # 765-1229. I had never heard of the stuff but decided to give it a try.

I decided to replace one of the leaking side covers and use this gasket sealer and a cork gasket. I cleaned the side cover and the engine with rubbing alcohol and allowed them to dry overnight. I followed the direction on the gasket sealer and it stopped leaking!! This is the first time since I have owned the car that the side covers has not leaked. I replaced the other one and it does not leak either.

Now I have replaced both side cover gaskets while the engine is in the car. I have used this stuff on my other cars and the leaks stop. I am sure that other people have used other sealents but this works for me.

One other hint, do not tightned the bolt too much. Snug finger tight and then a 1/2 turn with a socket.

Hear is a good discussiong about cleaning the valve covers:
http://www.mgexperience.net/phorum/read.php?1,1067088,1067632#msg-1067632

Good luck.

rob garrison
Knoxville TN, USA   usa


Another trick to fix the side cover leaks is to use an early gasket. Just use one for an MGA. According to John Twist at University Motors.

JMoore Avatar
John Moore
Clifton Park, NY, USA   usa

78mgb Wrote:
Quote: One other hint, do not tightned the bolt too much. Snug finger tight and then a 1/2 turn with a socket.

X2! Overtighening them causes them to warp. The spec is 4ft#'s of torque.





John Moore

'70 MGB, '68 MGBGT, '99 Land Rover Discovery II, '61 Austin Healey Bugeye Sprite

Blake Sonnier Avatar
lake charles, Louisiana, USA   usa
1956 MG MGA "Maggie"
1963 MG MGB
1972 MG MGB "Sweet Thing"
1974 MG MGB GT "None Yet"
1977 MG MGB "DIXIE"

Two MGB on that road and neither leak.. Not after I fixed the oil pan on each that is.. Don't use permatex Hylomar on you oli pan... I'll never use for anything.. permatex ultra black for me..





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P P
O, Ontario, Canada   can
1967 MG MGB GT "Maggie (GT From Hell)"

Not mentioned but equaly important is a good crankcase ventilation system. If you build up pressure inside the engine, it woll push oil out past the seals.

Pete

ingoldsb Avatar
Terry Ingoldsby
Calgary, Alberta, Canada   can
1971 MG MGB

To answer your question, ("Why do they leak"winking smiley it is really an issue of design.

There seem to be an unusual number of fittings, access panels, etc. The oil seal surfaces are not well designed. So, if you get enough holes in the block and couple that with badly designed sealing surfaces and chances are, at least one will leak.

Consider - the side panels. Bad enough that there are side panels, but there are two of them. Then, they use a sheet metal plate that deforms under pressure. If you put enough pressure on the plate to seal the outer gasket, the bolt itself leaks. I mean, look at the complicated excuse for a seal on the bolt itself. According to the factory diagram there is a rubber seal, a cup shaped washer, a regular washer and finally the bolt itself. I am not saying that it is impossible to seal (mine is currently sealed) but rather that the odds of getting every one of those surfaces to seal is slim. Then you get to do it all over again on the second cover.

For reasons unknown to the anyone, the front and rear bearing blocks have a slot cut out that is supposed to be filled with a strip of cork. Why? If they hadn't cut the slot, there would have been a nice flat surface for the oil pan to seal against. Instead, we add several more sealing surfaces and some unevenness - and we wonder why the pan gaskets leak?

Now we can talk about the numerous plugs and hoses that come out of the block. The oil pressure gauge hose, several plugs apparently used during construction of the block, the oil cooler hoses, the oil pressure relief valve plug. And did I mention the way the oil filter goes on. Most of the early 1970s cars have an "inverter" which makes the filter stand upright. Of course, this requires an extra seal for the adapter. But look at how the adapter itself is attached. A bolt with a copper washer that is supposed to seal itself. Mine is currently sealed - but that has been a gremlin for me.

And what about that rear main seal?! Those seals have been troublesome right from the factory. IMHO they simply don't fit snug enough on the crank. Fortunately the Payen equivalent is much better.

Now how many blocks have a plate on the front and back that needs to be sealed to keep the oil in? Another feature of our engine that is not found on most other engines.

So - as much as I love our little Bs, they really are challenging to seal. It CAN be done. But the chances of something somewhere developing a leak are much greater than on most modern engines. But yes - modern sealants do help a lot!



Terry Ingoldsby
terry.ingoldsby@DCExperts.com

Kent -In-KC Avatar
Kent Hartland
Kansas City, MO, USA   usa
1977 MG MGB

Well, that was very enlightening. I loved your rant, Terry. Go have a drink and breathe. ;^)

Thanks everyone! I'll let you know how I make out.

crustyoldfe Avatar
Bob .
At, Large, Canada   can

If your crankcase is ventilating properly (meaning it's under vacuum) it is physically impossible for the engine to leak oil while running. That is partly why the PCV system exists. If it didn't exist, blow-by would put a positive pressure in the crankcase and sealing it against leaks would be impossible. Oil would issue forth from every joint, crack, and crevice.

It also sucks the oil vapours and blow-by back into the intake manifold to be combusted rather than vented to atmosphere. This is the PCV systems primary purpose. Carbon emissions, pollution, and all that jazz.

In single cylinder (lawnmowers, etc) or uneven number cylinder (radial) engines , the pumping action of the backside of the pistons would also build up excessive crankcase pressure.

Bob

ingoldsb Avatar
Terry Ingoldsby
Calgary, Alberta, Canada   can
1971 MG MGB

Quote: If your crankcase is ventilating properly (meaning it's under vacuum) it is physically impossible for the engine to leak oil while running.

This is not true (but it certainly reduces the leaks). If you don't believe me, then take an engine with a properly operating crankcase ventilation system and (while running) remove the oil drain plug. If you are really confident in this statement you shouldn't need an oil pan! smiling smiley

But you are definitely correct that not having a functioning crankcase ventilation system will blow oil past the best seals and rings.

BTW - a trick I use to test for crankcase vacuum is to take the oil filler cap off (with the engine running) and place a flat card on the filler hole. If there is a vacuum it will suck down and not move. If it sort of floats then the crankcase ventilation is not working properly (or there is too much blow-by for it to cope with).



Terry Ingoldsby
terry.ingoldsby@DCExperts.com

crustyoldfe Avatar
Bob .
At, Large, Canada   can

Terry,

I know you're kidding about the drain plug and oil pan. We're not talking about massive oil leaks as a result of idiocy.
You are kidding, right?

Bob

I'm a little tense this morning. Trying a new type of coffee. Man!!! Good but really strong.



Edited 1 time(s). Last edit at 2009-03-29 06:12 AM by crustyoldfe.

Kent -In-KC Avatar
Kent Hartland
Kansas City, MO, USA   usa
1977 MG MGB

Neat trick, Terry. I'll remember that.

Jim K Avatar
James A. Krasnansky
Liberty, KY, USA   usa
1970 MG MGB GT "Chloe"
1971 MG MGB GT "Roscoe"
1972 MG MGB "Camilla"

Oil is over-rated.

"My MG stopped leaking oil!"
"Add some more, Mate. Add some more..."

Seriously - Terry put into words what I've always thought about our lumps - especially when compared to, say, Toyota. WAY too many inlets/outlets/attach points, etc.



Jim K is a grease-stained wretch

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