cause of crank oil seal leak?

after trying the xs 650 reed valve with no luck and replacing the standard seal with a slightly larger one my 850 was running pretty well. when i started losing power, dusk was starting to darken the sky. as i pulled across 2 lanes of motorway traffic onto a layby i thanked the gods as she cut out. i hadn't been run over (again) by a truck and had survived. oil pissing out of the head gasket, very little compression and 3 1/2 weeks until i return to australia, with the bike getting shipped at the same time. not enough time for an amateur like me to have it ready in time for shipping. time to call in reinforcements.
verdict: right cylinder busted piston and related issues. left cylinder rings in pieces. cam and followers worn. oil valve seized. etcetcetc
oil pump still has a strong flow of oil return to the oil tank. despite running well the engine was on its last legs. i doubt i could've foreseen this meltdown, she started second kick and sounded lovely, appeared to have good compression and ran pretty good until losing power on the m23 about 15 miles from home. this leak from the crank case to the primary may have been a symptom of the seized oil valve, being the point of least resistance.

If the seal is an original it may be less flexible than steel, you do say that one pistion assembly was "busted" and that the right had broken rings; your crankcase pressures must be over the top, amazing you could get it to run at all. I suspect that you are also loosing oil from every other seam.

' sorry to hear about your misadventure, sounds like you have some expensive work ahead of you. Without a history of your equipment it would be easy for the casual observer to make the assumption that your 35 to 37 year old engine had done yoeman service and deserves a complete renewal; hopefully the major bits (cases, barrell, head) are intact.

The real beauty of the Norton is that it has the sophistication of your average lawn mower/tractor; it is very easy to work on if you apply sufficient fore thought and patience. If you do the work yourself you will be able to justify purchase of all the tools; the knowledge base here is huge.

Best wishes for future success,

RS

i was not the only one who was surprised it was running , let alone running so well. apart from the crank seal to the primary, the engine was oil tight. go figure. the piston was literally broken to bits. i have been told that these bikes usually run incredibly well just before they blow up. the engine and gearbox were the only bits i didn't touch, bar valve clearances when i put it back together in 2008-09 and have no history of the bike before this time. upon taking the engine apart, it appears that one of the previous owners had done a semi rebuild of it, being that the crank looks in near new condition as do some other parts like the superblend bearings. now that the barrels have been honed to suit the new +40 pistons and seals and gaskets will be done, the cam, followers, rings, shells, big end bolts and nuts will all be replaced. hopefully will be all together before the pre arranged date for shipping. wish me luck.