[Mg-t] Moss rear seal - history

[Lawrie]

Fellow Listers,

After seeing a number of varied comments, I thought some history might 
be of interest. So,"here's the rest of the story" ....

I have installed probably 30 of the Moss rear seal conversions.
Initially I experienced mixed results so each time I checked more things and
learned more about them. I discovered a number of the things that Al Moss
eventually addressed in his instructions. As time went on, I realized 
that there
were two main reasons the seal didn't always work. As a result, I 
recently developed a way of making the kit work properly and
Moss agreed to my suggestions for changes to the kit and to my re-writing
the instructions. Their new 433-419 kit is as perfect as I could make it.

The problem with the original Al Moss design was that it presupposed the
crankshaft centerline to be exactly where the factory had put it. Most
engines have been line-bored or, at least, line-honed through the main
bearing saddles. Very seldom does this leave the crank centered as original.
(One I worked on was so far off to one side that, on the left, the seal was
crushed against the crank flange, while the other side didn't even touch the
flange!)

This problem was addressed by re-boring the holes that secured the retainer
half to the block to have flat bottoms instead of being countersunk,
making the hole size larger so the retainer could move around and be
tightened in place with button-head cap screws. Then a seal alignment tool
was provided in the kit to perfectly center the retainer around the flange
before tightening the cap screws and sealing the lower half of the retainer
to the rear main cap.

Once the seal could be perfectly centered, it needed to be positioned
properly relative to the flange. This is accomplished (temporarily, until
the next batch of retainers can be machined differently) by placing a shim
in the retainer to space it further back onto the flange.
Then instructions are included to have the back side of the flywheel
machined to a depth which prevents it from hitting the now-further-back
seal.

So, with the seal perfectly centered and positioned properly on the rear
flange, the Moss 433-419 kit should work every time (if the instructions are
followed properly!)

As for the need to machine the rear engine casting, this just isn't true.
Where the seal retainer fits on the back of the block is the
factory-machined surface where the original aluminum slinger was attached.
It's the back of the rear main cap that usually needs work, and this is
addressed in the instructions. Also addressed is the possibility that the
ribs on the block above where the retainer attaches might stand proud - the
only reason I can think of that any modification to the block itself is
needed.

Incidentally, I have just rebuilt the engine from my own TC, No. 7730, 
which was
last rebuilt in Australia in the early 1980s. Guess what I found in there? A
rear seal conversion very similar to the Moss one!
Correspondence with the Aussie rebuilder indicates that Al Moss based his
conversion on the Australian one. The improvement made was that Al's version
joined the two halves of the retainer and used the crank flange without
modification. The Aussie one involved machining the flange smaller (except
where the flywheel fits) and using a Volvo rear crank seal from a B18 
engine.
The Moss kit does not require modifying the crankshaft (other
than maybe fitting a Speedi-sleeve to give a good surface for the seal).

Lawrie Alexander