seal behind engine sprocket

[kew]

Hello all,
I have a 1964 model 16
I'm in the process of refurbing the bike and I have the primary chaincase outer off, when I went down to the shed this morning there was a pool of oil on the floor.
On checking I could see that the oil was coming out from the main bearing behind the engine sprocket. The bike was on the side stand and the oil had migrated from the oil tank to the crankcase, my next job is checking the oil pump.
Any way what I want to know is why isn't there a seal behind the engine sprocket, can one be fitted or something else done to stop the engine oil leaking into the crankcase?
Thank you

[SPRIDDLER]

In regular use there's no need for a seal to stop oil leaking from the c/case into the chaincase.
I suspect that the engine hasn't run for while, during which time oil has drained from the oil tank past the pump to a higher than normal level in the c/case (aka it has 'wet sumped'). When the engine is running the Return capacity of the pump is greater than the Feed flow, thus the oil level never comes anywhere near the overflowing level. Coupled with the bike leaning on the sidestand the excess oil has been able to overflow into the chaincase. This is quite normal.
Wet sumping is common and after being left for a while ( say a month or longer) it's customary to drain the c/case of the excess oil before starting the engine.
I have heard of one owner who fitted a sealed outer main bearing but that's a lot of work and entirely unnecessary if the bike is in use.

[kew]

Thank's for that Spriddler, it's what I expected to be honest.
I'll get the primary chaincase cover back on tomorrow and get the timing side off and sort out the oil pump.

[SPRIDDLER]

I've deleted this post to avoid misleading others. Thanks for the correction, James (Reynard24).
(My post referred to the incorrect and earlier plunger type of pump).

[Reynard24]

‘64 engines should have the Norton gear pump Neville and these do tend to wet sump if not regularly started.

[SPRIDDLER]

‘64 engines should have the Norton gear pump Neville and these do tend to wet sump if not regularly started.

Thanks James. I did wonder about that after posting and should've checked as my experience only extends as far as 1956.
It's useful to learn that, to quote the dealer's universal reply: "They all do that, Sir".