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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.
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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 03/28/2009 11:02AM 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.
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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 03/29/2009 06:12AM 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
Starbuck Avatar
Monte johnjulio
Greensboro, North Carolina, USA   usa
1967 MG MGB GT "Toaster"
1974 MG MGB "The B"
1979 Triumph Spitfire 1500 "Shitfire"

What causes leaks?

The original owners...the British Motor Corporation in Abington smiling smiley



"...They say that a man with two restoration projects is a poor man...I now have three...WTF was I thinking!?!?!?!?!?!?!"

1967 MGB-GT,1979 MGB roadster, 1979 Triumph Spitfire 1500 1974 MGB Roadster (retired, giving its life to be a parts car)

My 1974 MGB restoration at: http://mgbproject.blogspot.com/
My 1979 Spitfire restoration at: http://spitfire1500project.blogspot.com/
My 1967 MGB-GT restoration at: http://mgbgtproject.blogspot.com/
bobmunch Avatar
Bob Muenchausen
PC, Oregon, USA   usa
1968 MG MGB GT "Traveler"

All of the above about crankcase pressure, etc. is pretty much correct, Kent. However, one thing often overlooked, especially with rotary seals such as the front and rear crank and other shaft seals throughout the car is the condition of the surfaces that these seals have to run on.

With vehicles this old (and often times poorly treated by DPOs and sloppy mechanics) the likelihood that the surface on which the sealing lip runs is worn or damaged is pretty great. Certainly, not all cars or their shafts will be in poor shape, but even tho some are OK, many will not be. To simply replace a seal without addressing the mating surface condition can very definitely determine the longevity of that seal's ability to seal properly.

When I was younger, hitting the shaft with some crocus cloth to smooth it up was thought to be "good enough". But what we find today is that the type of surface that seal is intended to run on is a very special sort, http://rlhudson.com/Shaft%20Seal%20Book/design-shaft3.html and crocus cloth treatment is not really what will make a seal run and seal for a long time. It has to be better than that.

To that end, there is a product called a Speedi-sleeve which you may be familiar with. Its primary purpose is to provide not only a nick and wear free surface for the seal lip to run on, but of the correct finish for long life. Folks (and I have been among them) who install new seals but find that they don't seal for too long often blame poor seals or other problems like blowby, but in truth, many times, perhaps most of the time, even a cheap seal would have done better had the shaft's surface been renewed to its correct finish.

If you explore R.L. Hudson's website (above) you will find a true wealth of information on just this topic.

As for gasket sealing? There are many factors as have been said, but probably the most important is still cleanliness. Most of those sealants on the market today, from your grandfather's Indian Head shellac sealant on thru to the more exotic types are capable of sealing properly if a few things are observed. 1) cleanliness of the mating surfaces, 2) that those surfaces are indeed flat and true, and that when setting a gasket, the sealant is allowed to "cure" a little before applying full torque or tightening pressure. Add to these that the gasket and sealer materials must be suitable for the purpose (pressures they will hold, temps they will resist, chemicals they will resist, etc).

Consider the period in which these cars and their components were engineered and it is easy to see that the materials and technology for sealing have progressed well beyond what was extant at that time. We should be able to button these cars up much better than they were originally, and with careful workmanship and knowledge of materials and components, there is really no good reason for them to not meet current standards. My wife's 2003 Hyundai Sonata has 101K miles on it and it does not leave puddles and mark its territory as we like to say. The main reason is, more than anything else, that the lessons of the previous 4 decades of engineering and materials development have made it possible for most modern cars to keep their fluids where they belong. That we can make use of this knowledge and these materials on our cars is a boon to us and takes up the slack between late 50s tech and where we are today.



"All that my contradictory experiences demonstrate, sometimes, is that things and materials don't always follow the course of our commonly accepted thinking about them, but end up sometimes besting our knowledge of them."


SU Carb setup instructions ~ You don't need smog gear to need/use these factory instructions.
>>>https://www.dropbox.com/s/dgjgbxszv1h22hy/MG%20EMISSIONS%20MANUAL.pdf

MGB GT cutaway car photos can be found here >>> http://www.cibolas7.net/resources/cutaway.htm

A thorough guide to rubber rotary seals as used on your crank, axles, etc >>> http://www.rlhudson.com/Shaft%20Seal%20Book/index.html
ingoldsb Avatar
Terry Ingoldsby
Calgary, Alberta, Canada   can
1971 MG MGB

Quote: 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?

Mostly. smiling smiley To be absolutely accurate, the depression (vacuum) in the crankcase is quite minor. You are correct that that *should* be enough to prevent leaks but there are a couple of caveats. First of all, if oil pools against a hole, then the weight of the oil exerts a pressure that may very well overcome the slight depression. That would be the case if you pulled the drain plug. Similarly, if oil is spurting towards a weak spot then that may also be enough to overcome the vacuum.

Also, a lot of leaks are from pressurized lines (like the oil pressure line) that are external to the block.

But you are (almost entirely) correct - and it is essential to have a properly functioning PCV system. And I knew exactly what you meant - my comments were meant to be tongue in cheek.



Terry Ingoldsby
terry.ingoldsby@DCExperts.com
BManBrian67 Avatar
Brian M
HB, California, USA   usa
1967 MG MGB MkI "MI MG"
2000 Porsche Boxster S "Got Box S"

The MAJORITY of leaks on an MGB engine are caused by people overtightening the gaskets. The side covers, the pan gasket, and the valve cover are these main ones that get torqued down on too hard and they leak as a result of this.

Proper torques and some modern gasketting material and cement are usually enough to creat good seals.

B
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