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MG MGB Technical - Installing Overdrive, Questions, Seals & Clutch

I finally found an affordable LH side-fill overdrive for my 77 B, and I'm trying to get organized for the installation.

It’s been a few years since I had an engine out, and I can’t remember the rear crankshaft oil seal details. Am I correct that I can replace it by removing only the flywheel, and that the backing plate can remain in place?

The last time I installed a rear seal, I think the Payen oil seal was recommended. Is that still the case? I have seen one vendor offering a Gaco/Angus black oil seal at a premium price (about $17). Does anyone know anything about these?

Apparently the pilot (spigot) bushing can be 1 inch or 1-1/2 inch long. Anyone know which was used in 1977?

My 77 has about 50k miles on it, and I am reasonably sure the engine has been out at some time. I was not intending to change the clutch components unless they look worn, or unless they are not Borg & Beck. This is not so much a matter of being a cheapskate, but more a matter of lack of faith in the quality of some of the new parts compared to the older parts.

So, to assess the existing clutch, does anyone know the thickness of a new clutch disc? Also, does anyone know the new height of the carbon on the release bearing?

Alternatively, am I being an idiot not to replace the clutch as a matter of course, and are there no quality issues with the new Borg & Beck clutch and release bearing?

Thanks,
Charley
C R Huff

CR-
Yes, the backing plate can remain in place. The original crankshaft rear oil seal worked just fine before the advent of the sealed crankcase, but the vacuum present in the sealed crankcase of the later engines tends to draw stuff in, making the dust exclusion feature of a double lipped oil seal a plus. Most double lipped oil seals have the outer lip reversed in order to prevent ingress of dirt or air that can do damage to the seal and thus interfere with the maintenance of the vacuum inside of the crankcase. On the other hand, a true double-lipped oil seal would have both lips in the same direction, for good sealing against fluid escape. 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. Be sure to put a thin smear of red rubber grease onto both the sealing lip of the seal and its seating area on the shaft. 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.

Your 1977 engine used the 1" pilot bushing. Prior to installing the spigot pilot bushing into the spigot bore of the crankshaft, be sure to slip it over the input shaft (first motion shaft) to determine that its Inside Diameter (I.D.) is not too small. Due to the wicking properties of the saturated bush, the use of sintered bronze for spigot pilot bushings is a standard practice in the automotive industry. It consists of granules of bronze pressed together under high pressure and heat in order to form a rod that is then machined to form a bushing. The pores in the sintered bronze set up a circulation system for the oil while the shaft is rotating. Soak the new spigot pilot bushing in 10W oil for a few days before you install it. The sintered bronze alloy will soak up the oil until it is saturated, ensuring good lubrication. When installing the pilot bushing, you will need to be careful not to use too much force as any lip that you might create on the Inside Diameter (I.D.) will interfere with the free movement of the first motion shaft (mainshaft) and cause it to squeal when it is cold!
Stephen Strange

Stephen,

Thanks for the info. I have a few follow up questions.

Your choice of the word "adapter" with respect to the seal makes it sound like something that comes with it like the installer that comes with a Speedi-Sleeve. Is that so, or do you just mean a seal installation tool?

Also, I have never owned or seen any red rubber lube. Is it typically available at an auto parts store, or does Bob carry it at Brit-Tek?

Charley
C R Huff

"Soak the new spigot pilot bushing in 10W oil for a few days before you install it."

This can be done in about 15 seconds as follows: Place the bushing on end on one thumb, fill the bushing with oil until it brims over, place you other thumb on the top of the bushing (being double jointed here helps) and press your two thumbs together until you see oil oozing out of th pores of the bushing - a two day soak in 15 seconds! Cheers - Dave

Note, learning of this method has been a wonderful time saver for me as I would always forget to soak a bushing until I was just about to install it, then I would have to stick the bushing in oil and wait the required two days.
David DuBois

At 50k I would never leave the clutch in, regardless, **epecially** if you are going to the trouble of removing and splitting the engine and gearbox anyway!. The carbon ring on a new B&B I have is 5/8" thick, with 1/4" protruding. But I've changed a clutch (history unknown) where there was still some protruding even though the friction plate was down to the rivets one side with all the lands worn off both sides and slipping in 3rd. You should be OK with a new B&B, but make sure the release bearing doesn't have a roll-pin in the side of the casting. These were around a few year ago and are known to cause the carbon ring to break up in short-order, see http://www.mgb-stuff.org.uk/clutchtext.htm#release
Paul Hunt 2010

Thanks Paul,

If I knew the clutch had 50k on it, I certainly agree with you. Because the engine in this car was not black when I got it, I'm thinking someone had it out, and the clutch may have already been replaced at some time.

Good trick David. Since I will have plenty time, I'll probably do both. I don't recall seeing straight 10w oil. Is it difficult to find? I think I might have used 20w when I did my 68 GT.

Charley
C R Huff

This thread was discussed between 11/07/2010 and 12/07/2010

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