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MG MGB Technical - Rear Main Seal Fitting

With my late 18V engine about to return from the machine shop, I am seeking advice on the best method for getting a leak-free rear main seal.
With the engine fully stripped down now, would it be better to fit the seal into the backplate before attaching the backplate?
I have bought a LUF1002 seal with the plastic installer, so would it be better to use this after fitting the backplate?
I plan to use a little red rubber grease to lube the inner seal and crankshaft, and i'm wondering if it is good practice to use a sealant on the outside edge of the seal to help prevent seepage. Would Permatex Aviation do the job or are there better alternatives? Is it best not to use any sealant?
Your advice will be gratefully received.

ph barton

The cork strip installs into the engine block, then the plate is installed, compressing it. Getting the cork seals for the front and rear crankshaft main bearing plates to their correct lengths requires some patience. The recess into which they fit must be both clean and unpainted, otherwise the gaskets will eventually seep oil. Insert the ends of the cork seal into the recess so that its middle bows upward, then gently press its ends outwards towards the ends of the recesses. Should the cork seal still bow upward in its middle when light pressure is exerted upon it, do not attempt to force it down. Instead, remove it and use either an Exacto knife or a single-edge razor blade in order to cut 1/32" (0.8mm) of material from one end. This should be achieved with care being taken to assure that the cut is perpendicular to the longitudinal axis of the cork seal; otherwise, there will be a likelihood of leakage from the poorly-cut end. Repeat this process until the cork seal just compresses into its machined slot. The finished cork seal must bow slightly above (1/16") its machined slot. This is so that the cork seal can be compressed in all planes in order to fit the length of the groove when both the oil sump and the engine plates are torqued into place, and it is this compression that helps to promote a good seal.

Use a putty knife in order to coat the cork gasket with a smooth, even, thin layer of Permatex® Ultra Black RTV Gasket Maker sealant, forcing the sealant into the pores of the cork by means of the flat side of the putty knife. That will produce a smooth, even, flat coat that will compress evenly with no high or low spots that will be prone to leakage. Be sure to let the sealant properly cure for approximately 30 hours prior to attempting to trim away any excess material from the edges using either an Exacto knife or a single-edge razor blade prior to installing it. This is possibly the best silicone sealant on the market, able to withstand temperatures of as much as 5000 Fahrenheit (2600 Celsius). Be sure to let the sealant cure for several hours prior to attempting to trim away any excess material using either an Exacto knife or a single-edge razor blade prior to installing it. This will result in a rubberized gasket that will not become saturated with oil and consequently ooze oil onto the sides of the engine, and from there onto the garage floor.
Stephen Strange

Phil.
To answer your question-
My preference is ,if the engine is together then yes you have to do it with the plate on but if it's apart as yours is, the best way is to fit the seal to the plate first, it's easier to get it fitting nice and square where you can get a good look at what you're doing, then poke the sleeve through the seal and fit the plate up to the block lining the sleeve up with the crank as you go -don't forget to remove the sleeve when you're done
A smear of permatex ultra on the outside won't hurt, but not really necessary but it does act as a bit of lubrication to make the pressing in of the seal easier without damaging the outer part
NOT a fan of rubber grease on spinny bits,a smear of engine oil or some assembly lube is the go on the crank/inner seal lip
With Steven,s guide to fitting the cork seal, I don't do it that way, I leave it as long as I can to get a good compressed fit lengthwise (cork does shrink)and glue it into place in the cap groove with contact cement to hold it there while fitting the plate and then a smear of ultra over it when fitting the oil pan
willy
William Revit

As always, fantastic advice from Stephen Strange and Willy Revit. These guys have accumulated huge depths of knowledge from their combined decades of experience and their astute observations over these years.

As a rank amateur, my own additional modest suggestion: It takes remarkably little wear on the back end of the shaft to get a leak from here after reassembly. As they say "ask me how I know?" I had precisely this problem when rebuilding a low mileage 18V engine, destined for my MGA. A Speedi Sleeve (and another new rear seal) solved the problem.

Interestingly the 18GB engine in my 1965 MGB, was rebuilt (I thought prematurely) at 95,000 miles, by my obsessive motor mechanic father, in 1979. The car and engine have now done a further 145,000 mile since then; the rear seal, and indeed the entire engine, has remained utterly leak free to this day.
T Aczel

Thanks for that,
So is a speedy sleeve a prudent addition in most cases, even if the rear crank is in reasonable condition? There didn't seem to be a groove on the back of the crank, just a black ring. Smooth to the touch.
My crank was in good condition and the journals only required polishing, but i'm wondering if the sleeve would be a "belt and braces" thing. I really don't want to be pulling this apart again a few years down the line!
A SKF sleeve costs around £31 ($43 US) over here, and i'm thinking that might be money well spent.
ph barton

That LUF1002 seal is a good seal
If the crank's good there's no need for a sleeve
William Revit

This thread was discussed between 22/05/2021 and 23/05/2021

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