Triumph crank seal

Why is this installed open side out while Norton is just the other way around?

You mean the timing side ?

The oil pressure is fed to the end of the crank via the timing cover, so that's where the pressure is, so that's where the spring side of the seal faces.

seattle##gs said:

Why is this installed open side out while Norton is just the other way around?

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I take it you mean the drive side crank seal in the 'sealed' (pre-'70) non-breather Triumph primary drive (also BSAs) and not the timing side crank seal?

It would seem either BSA/Triumph were more concerned about keeping the primary oil out of the engine rather than keeping the engine oil out of the primary, or perhaps more likely that the seal lip would not invert from excess crankcase pressure.

primary side. the answer for triumph would be to engineer a better breather. By 1970 they gave up and removed the seal.

Never worked on an A65 so it may be as the Triumph twins, but all the BSA Unit Singles have the primary crank seal as per the Norton until the B50 when it was deleted for primary breathing. As the first Unit Single the BSA C15 was based on the Tiger Cub and so follows Triumph engineering practise to a degree its odd.

kommando said:

Never worked on an A65 so it may be as the Triumph twins, but all the BSA Unit Singles have the primary crank seal as per the Norton until the B50 when it was deleted for primary breathing. As the first Unit Single the BSA C15 was based on the Tiger Cub and so follows Triumph engineering practise to a degree its odd.

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I had a feeling it was the same for BSA twins as Triumph twins but perhaps not?

Not 100% definitive but this is a pic of an A65 primary oil seal installed (Its hosted on photobucket so you need the chrome photobucket embed extension to see it), the factory manual just says the seals are orientated so the open side faces the part to be sealed so next to useless. Haynes has a copy of the parts book scaled too small to be clear but looks to be showing the open side facing the main bearing but it is haynes.

So looks to follow Unit Single and Norton.



and another but again photobucket

Ah, the age-old debate about "what is the right way 'round for the crank seal"...

A big 360 twin, on the piston downstroke, can blow right through a crankcase seal if it is placed with the sealing side toward the primary. Not optimal. Try it on a Commando and witness the wonder of downstroke compression!

The SLIGHT chance that it can draw primary chain lube into the crankcase is virtually nil, ESPECIALLY with standard crankcase breathing plumbing working properly. Furthermore, if you run the proper primary chain lubricant (per manufacturer recommendation), that lube will do absolutely no harm to the engine.

Of Couse the PRE UNIT , with the Brass Bush , dosnt have this problem .

And theyre fine with 20 thou of ball race wear , which may well be regarded as Clapped Out . Also as further crank alignment / stiffening .

Of course a rubber seal & circlip were cheaper , and less critical as regards ' line boreing ' .

We wont mention the ignition , at this time . either . :wink:

seattle##gs said:

Why is this installed open side out while Norton is just the other way around?

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See post from John Healy on the Britbike Forum (http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=395472):

"If it is a 1963-1969, that breathes through the end of the camshaft, it uses a seal and the spring faces the sprocket.

If it is a 1970 or later, that breathes through the primary (no matter what the 1970 parts book says), it does not use a seal.

While you may have found seals in non-seal cases, or seals with the spring facing inward, it is not how it was designed to work. It was not how they were installed by the factory.

Is there any harm in installing a seal backwards in a 1963 to 1969? Other than cases where one chooses to use automatic transmission fluid in the primary, probably not.

May I quote the Overhaul manual written by Tom Gunn and used exclusively in the Triumph "Tri-Cor" Dealer Service School:

"o) Install the primary crankshaft oil seal open side (wire ring side) facing out toward the primary. (note: authors underline) DO NOT drive the seal all the way in - it must not seat against the drive side bearing and cause a drag on the crankshaft."

Is there any harm in installing a seal in a 1970 or later, that breathes through the primary, Yes! Basically the engine will not breath and the crankcase pressure will rise. This increases the chances of oil leaks and premature gasket failure."