Katana Owners Club U.K.

Pootling along on my 650 no faster than 60 and everything is fine. Get to the m/way, give it a few beans and take it up to 70 and it pisses oil over my left foot. I cannot for the life of me figure out where it is actually coming from. Cleaned the whole bike and then ran it on the centre stand at high revs but sod all happens. It seem that it only occurs when actually riding and at speeds over 55/60.
Looking on the bright side, my boots are waterproof.

Last time I saw something like that was with a Detroit 12V71 (big 2 stroke diesel) driving a nitrogen pump. Turned out to be a bent conrod caused probably by hydraulic compression in one of the cylinders. At anything above 60% power it blew oil out of the breathers.
As we always ran them flat out it coated the main deck of Shell Leman Alpha in engine oil.

But that's probably not what's going on with your Kat.

As the difference between running an engine off load and the same revs on load is quite significant. It could be crankcase compression blowing oil out of the breathers or into the airbox. Or it could be the loaded engine is causing a hose or fitting to the oil cooler to pass oil

Does your Kat still have the airbox? Or an oil cooler?

Another possibility is the half moon seals on the cylinder head...

Are there no signs as to where it is coming from other than your left boot?

Still going for the alternator cover , the silicon goo will hold it until it's under pressure .....
Best remove clean everything flat and use proper gasket , just to eliminate it., after that you are looking at pressure as in half moons etc.

Cheers lads, I 'll try that and let you know.

Is that the same 650 that did that on the way to the bikers loft in Belgium? that was left alternator cover wasn't it then?

I did have a similar experience on my first 1100 with oil on the left foot at speed and that was a blown fork oil seal - at speed there was enough air velocity to blow the oil back onto my foot.

You checked the gearshaft seal? Also: A worn out bearing might allow the shaft to move slightly backwards once under load. an old seal won't make a proper job then.