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November 12, 2020

Rear Main Seal

The Triumph six cylinder engines had a main crankshaft seal housed in an aluminum casting at the rear of the crank case.  The housing also bridges the gap in the sump mounting flange, and accepts two of the sump fasteners.  The machined mating surfaces of my seal housing after 50 years weren't all that flat.




A little linishing quickly fixed that.  I considered installing some inserts in the threaded holes for the sump attachment, but these don't really seem to present the problems that the ones in the sealing block at the other end of the engine do.  I assume it's because the aluminum of the seal housing is a much stronger material than the zinc alloy of the sealing block.




So I gathered all the parts necessary to install the rear seal.  Those are the original bolts, but new washers.  Since one of the attachment holes actually opens to the inside of the crankcase, its bolt gets a copper sealing washer instead of a split lock washer.  I normally anneal copper washers, even if they are new.




So this is where the seal and housing go.  The engine is upside down in many of the pics below.




The seal was then installed in the housing, the gasket applied, and the assembly was slipped over the crank end.
 



The seal of course is self centering on the crank, but there is the possibility of shifting the housing to one side slightly when tightening the bolts,which could result in an oil leak.  The factory apparently thought centering was important enough that they specified a special tool for the job.  The tool is obviously not available today, and I'm not even sure what it looked like.  The principle is simple, though.  The crank end is 2 7/8" in diameter, while the opening in the housing is 3 1/16".  So the space between the crank and housing needs to be 3/32" all around.  I found some 3/32" gas welding rod and cut a few pieces but, not being precision material, they were a little loose.  Four little pieces if 0.001" brass shim stock was all it took to make them a snug fit.




Torqued the bolts, and checked this task off the list.





This was a simple little job, but I thought the centering operation might be of interest to some.


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