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MG MGB Technical - Rear Main Seal

The rear main seal on the 18V engine is starting to drop more oil so I'm thinking of pulling the engine. Haven't been reading about improvements for a while, so was wondering if there is a better rear seal available. thanks, Tyler
C.T. Irwin

Tyler-
Yes, there is a better seal available. An uprated single-lip crankshaft rear oil seal that was used in the version of the B Series engine found in the Sherpa van will do an excellent job of keeping oil inside of the engine over the long term (Rover Part # LUF 10002). Contrary to rumor, this crankshaft rear oil seal is not a double-lipped design. The seal dimensions are: Outside Diameter (O.D.) 4.125” (104.775mm), Inside Diameter (I.D.) 3.500” (88.9mm), Width .375” (9.525mm). Being made of Viton, they are not prone to failure until thermal conditions rise above 4500 Fahrenheit (232.20 Celsius). This crankshaft rear oil seal can be obtained from Brit Tek (Brit Tek Part # AHU2242). When you examine the new crankshaft rear oil seal, notice that one side of the seal has a sharp edged lip while the other side does not. The side with the sharp lip also has a spring around the circumference of the rubber. The spring holds the rubber in contact with the shaft and the sharp edged lip runs on the shaft. The sharp lip is what actually seals the shaft. On the spring side you can see that oil under pressure would tend to assist the spring in keeping the rubber in contact with the shaft. Likewise, if installed backwards, oil pressure on the side opposite the spring would tend to lift the rubber and would oppose the spring, defeating its purpose.

Simply use a screwdriver to pry out the old crankshaft rear oil seal. Installation of the new crankshaft rear oil seal is quite straightforward. Make sure that the engine backplate is held in place with the machine bolts that are only finger-tight so that it can be moved by gently tapping it with a soft hammer. This may be necessary in order to properly center the new crankshaft rear oil seal. Clean up the rear of the crankshaft, as well as the hole in the engine backplate. Slide the plastic adapter that came with the crankshaft rear oil seal over the end of the crankshaft, with its big end first. Be aware that when installing an oil seal, many builders simply put a thin coat of oil onto the shaft and then slide the seal into place. This is an adequate method if a mechanism is to be put into service shortly, but if it is to await for several days, or even weeks, capillary action and gravity can interact to cause the oil can drain away, leaving the sealing lip of the oil seal to run dry against a shaft that is unlubricated until circulating oil reaches it. A better method is to put a thin smear of red rubber grease onto both the sealing lip of the seal and its seating area on the shaft. Next, apply a thin coat of oil onto the rest of the shaft. Oil the outside of both the adapter, and then slide the oil seal over the adapter until it meets up with the engine backplate. Grease the outer rim of the new crankshaft rear oil seal with red rubber grease. Do not tap the new crankshaft rear oil seal directly with a hammer when installing it onto the engine backplate as this can cause it to distort. Gently tap the adapter all around its circumference with a small hammer in order to drive the oil seal into place. Gently drive the new crankshaft rear oil seal in until it is flush with the engine backplate, and then pull off the adapter. The red rubber grease will stay in place indefinitely on both the shaft and the lips of the seal. A smear of oil on the outside surface of the oil seal will, depending on the material of which the oil seal is made, help to swell the seal shut against the shaft. Prior to pressing the engine backplate onto the locating dowels and before torquing the 3/8”-24 UNF machine bolts of the engine backplate, give the engine backplate a gentle rotational wriggle in order to guarantee that the lip(s) of the crankshaft rear oil seal are square against the journal of the crankshaft, thus ensuring a leak-free fit. This will also help to settle the new crankshaft rear oil seal and thus make certain that it is absolutely centered onto the crankshaft and is not pre-loaded by means of the engine backplate being slightly offset. Install the crescent-shaped locking plate (BMC Part # 1H 1021) with its four 5/16”-24 UNF machine bolts, and then bend the tabs upward in order to retain the bolt heads in position.
Stephen Strange

Hi Irwin,

As Steve says, but I would also recommend the fitting of a Speedi Sleeve, a thin stainless steel tube, that fits over the shaft and gives a perfect surface for the seal to run on. Here in Oz, they are available from bearing suppliers. Your leak may not be the rubber seal, but a groove in the shaft. The speedi sleeve fixes this.

Herb
Herb Adler

thanks Herb and Steve,
I got the double-lipped rear main seal (Payen NB772)(88.9x104.78x9.52mm) and SpeediSleeve (SKF 99346)(3.497-3.503 in)from Brit Tek. While engine is out, also got a new throw-out bearing (Powertune PTHD3317)to install. And thanks for instructions. See you at MG 2011!
Tyler
C.T. Irwin

Steve,
Sounds like the rear plate does require removal ("pressing the engine backplate onto the locating dowels"), if so I better get a new rear plate gasket (I'm sure the old one is adhered to the plate). Also: I received no "plastic adapter" with the seal. Is this a seal driver? Any good substitute for red rubber grease? I'm installing a speedisleeve. What's better: install the lipped end (that's later cut and torn off?)on the crank first, or the other end? Thanks for your help.
Tyler
C.T. Irwin

Hi Tyler,

You don't need to remove the backing plate, just be very careful when removing the old seal. To remove the seal punch 3 holes roughly equally spaced around the seal (don't drill, otherwise you will have metal swarf everywhere, a suitable punch can be made by grinding a point on an old screwdriver) insert small self tappers, a turn or two, till they just hold, then use a pair of pliers to pull on them, thus pulling the seal out.
The speedi sleeve goes in with the lip first, its the only way you can get it in, as the insertion tool bears against this lip. The lip can stay in place, as it is well out of the way of the seal. NOTE the requirement for a non setting sealant, I use Permatek.
After inserting the sleeve wrap some tape around the very edge, this is so that the sleeve doesn't damage the seal as its pushed on. Very gentle tap the seal into place by using a piece of chip board with a hole cut in it, such that it just fits over the end of the shaft. Place another piece of chip board over the top and gently hammer it in. Make sure that you don't let the seal go in on an angle, or it will distort and then won't seal. When the seal is fully inserted remove the tape.
You don't need to use rubber grease, as the seal is resistant to mineral oils , after all that's its job. I use molybdenum disulphite grease (molygrease), whenever I do a seal.

When I did mine I found that the sleeve was about 1/8" longer than the shaft, after having installed it. What I did was to bend the edge outwards and the flywheel has a boss that then fits into this. The other solution would be to cut a bit off before inserting, though I would be worried about distorting the sleeve.

Good luck

Herb
Herb Adler

This thread was discussed between 28/02/2011 and 09/03/2011

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