This is one of the great mysteries of small-blockdom!
Some bikes can, suddenly and with no warning, drink an entire sump full of oil with no warning! The difference in this case is that there is evidence of where the oil is going, it's obviously being burnt. The weird thing is that in many cases there is no evidence. Even when the engine is stripped subsequent to it running its big ends, (The usual result.) the combustion chambers are clean, the plugs aren't covered in carbon and the piston decks rarely look washed!
What is particularly vexing is that bikes can behave perfectly normally for years and then with no change of usage suddenly do it and kill themselves stone dead! To my mind it has to be ring related as when the piston and ring design was changed with the arrival of the single TB models the problem vanished and has never recurred to the best of my knowledge.
In this case it is obvious that oil is being burnt. The question is is this the result of the crankcase pressurising and blowing the oil into the breather box which is then filling up and poring it into the inlet tracts and thence to the cylinders through the inlet valves or is it being pumped up past the rings?
First thing in my book would be to make sure the breather system wasn't clogged. After that it would be time to whip the heads and barrels off for a looksee. It might be something as simple as a gasket burnt through to a pushrod tunnel. We're the heads ever RE-torqued at first service?
Pete
