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MG MGB Technical - After pulling engine and trans

OK, pulled the engine and trans, separated the trans from the engine and low and behold I don't have an oil leak from my rear seal. This was the reason I was pulling everything. I would use 1 quart of oil in less than 1000 miles and I could see it on everything under the car. The trans had most of it and I suspected that was because it is behind the motor. After pulling the trans and pulling the clutch and pressure plate everything is bone dry in side. SO, do I do a replacement of the seal or not mess with it. I am going to replace the clutch and pressure plate because its out and I have a new trans to put it but I am a little perplexed.
Peter Murray

Most people recommend replacing the rear seal anytime the engine is out. That said,on the few MGB engines I have removed, none had a leaking main seal. If it were my engine I probably would not replace it unless I was removing the rear plate. The seal contact area on the end of the crank usually has a worn area under the seal, new seals may leak unless the wear on the seal surface is taken care of by use of a repair sleeve or positioning the seal so it contacts a slightly different area on the crank.

Clifton
Clifton Gordon

So what was leaking?
Steve C

Check the oil pressure sender and hose. Also, check the joint
between the head and block (head gasket leak near the rear
rocker pillar).

As a rule, I replace both rear main seal and trans shaft input
seal whenever I have things apart at that level. Years ago,
I did a clutch change, and then about 3 weeks later the
rear main seal leak began leaking. I pulled everything out
and changed the seal. Then about a year later, the trans
input shaft shaft seal began leaking and ruined the clutch
disk. No more. I change both seals at every clutch change.
Daniel Wong

Peter. I find it best to steam clean the engine, or to use some form of engine cleaner, then try to determine where any leaks are coming from. This has to be done before the engine is removed, but may be of help to others who have similar problems.

As to areas of leakage, they are numerous. The most common areas that leak are the rocker arm cover gasket, sump gasket, and tappet cover gaskets. Less prone to leak areas are the timing chain cover, the oil pressure relief valve, the oil filter assembly, the oil pressure take off fitting, the oil line fitting at the upper right, rear of the engine and any plug that goes into any oil galley.

The best thing you can do, when the engine is out, it to clean it throughly--much easier to do when the engine is not in the car, and tighten up all of the various bolts and plugs to ensure they are fully tightened.

As to Danny's comments about replacing the front seal on the tranny, I agree. Also a good idea to have some extra shims as about fifty percent of the ones I have done had had broken shims inside the front cover.

Les
Les Bengtson

After reading all comments and looking again with renewed eyes (read, tired from removing everything)It appears the leak is from the front trans seal. So now I have issues with the engine using an extraordinary amount of oil with nothing visible as to where it is going. Les, I am going to clean everything as you suggest, tighten bolts, replace gaskets where possible and I am replacing the transmission. Again thank you all for your input and I will keep you in the loop as I progress
Peter

Peter, Double check those tappet cover gaskets. They are notorious for getting hot, shrinking their gaskets and leaking copious amounts of oil down the left side of the block. Ray
RAY

I would remove the manifolds, plug all intake areas to keep fluids out, degrease the block and look where your leaks are, replace the tappet cover gaskets. If you have an engine stand, I would turn the engine over, remove the pan and do a super job on front and rear seals and then the pan gasket. then paint the block. The paint helps seal the gaskets.

I also used one of the neoprene gaskets on the valve cover.

No leaks in my 67 after the above treatment.
Bruce-C

Peter-
One of the most common causes of leakage is indeed a bad rear main seal, and old, tired gaskets is another, but one of the surest way to provoke these into failing is overpressurization of the crankcase. Bad compression rings are usually the origin, but a parially blocked condensing system will surely push things over the edge. When you remove the front cover of the tappet chest you will notice that it has an oil separator, which is a provision for condensing oil mist. Because this design feature is often partially clogged with dried oil residue, it should be soaked in a strong solvent such as carburetor cleaner and then thoroughly blown out with compressed air prior to reinstalling it. If it is reinstalled in a partially clogged state, it will inhibit the outward flow of gases from within the crankcase, sometimes to the point of creating overpressurization and attendant oil leakage from whatever weak sealing may be present anywhere on the engine. In addition, it will not be able to properly condense oil mist. The oil mist will be drawn into the induction system and reduce the octane level of the fuel/air mixture, which in turn will lead to preignition. It will also result in carbon buildup on the roof of the combustion chamber as well as on the valves and the piston crowns, which can also result in preignition.
Steve S.

Peter,

I am not familiar with the engine breathing system on a US car, but check it is all in good condition and that it is not simply vented to a hose open to the ground. If the breathing tubes and the condensing gause are caked in old oil and don't do their job you can loose a huge amount of oil very easily, especially if the system is connected to the carbs as it is in the UK. The oil is burned in the engine, but it can be difficult to spot this from the tail exhausts.

Iain
67 BGT

PS If the current main rear seal is not leaking don't touch it!!
I D Cameron

Are the currrent seals available for the tappet covers on the MGB correct? I have heard you should use gaskets from a MGA for these? Wondering?
Mike
MK Mike

Mike. You should contact John Twist through his University Motors Ltd website. Best method, if you are free at that time, would be to call him during his tech hour. John was the first person, whom I know of, who recommended the use of an MGA tappet cover gasket on the MGB engine. Do not remember whether it was for the front cover, rear cover, or both. But John should be able to set you up with the best system possible. Then, you can post it here and the rest of us can print out your post for future reference.

Les
Les Bengtson

I would like to THANK YOU all very much for your insight and your interest. I think I can safely say, when asked, that I had more than twenty helpers while I was doing this little job.
Peter

I had a severe oil loss on an MGA 1500 motor that got up to about a quart every hundred miles or so. Finally found it as occurring at a headgasket leak at one of the pushrods. The engine compression was pressurizing the crankcase and blowing out the breather. A new headgasket solved the problem. Yes someone else suggested this as a possible cause and though I thought it odd, he was right.
Wayne Hardy

Les
I now remember that is who I heard it from. John Twist says us a MGA thin cork gasket on the FRONT Cover. You can go to You Tube and type in University Motors and view his video on MGB Oil leaks, where he mentions it. Lots of great stuff from him.
Thanks
Mike
MK Mike

I read these comments with great interest. I have a 79 MGB, with no apparent leaks, small amount of smoke, but a quart of oil about every 200 miles. No sign of pressurization. Compression all 140-150's. If the leakage was due to a head gasket, wouldn't the compression indicate this?

Inspected valve stems previously, and found there were no seals, installed the Ford umbrellas, helped some, but consumption still excessive.

What's the most logical answer?
James Huggins

High oil consumption can be via the crankcase breather, and is relatively easy to confirm if not cure. If due to bores compression *would* show this, particulary a high difference between dry and wet readings. Worn valve stems/guides less so I think, but these tend to cause clouds of blue smoke when accelerating after idling or being on the overrun a while.
Paul Hunt 2

This thread was discussed between 02/02/2008 and 11/02/2008

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