Here goes;
some weeks ago I did an oil and filter change. Warmed up the motor then drained the oil, remover filter etc. Put on new filter and put in about 3.0l of oil. This completely filled the oil sight glass window, but didn’t worry me as once the motor was started the filer would hold some etc. Anyway, some days later (had other maintenance items to do) started her up, a bit reluctantly, and went for a short trip around the block to make sure all was good. In a couple of minutes smoke was bellowing out the exhausts and the rear tire coated in oil.
Looked like the crankcase was being pressurised (too much oil) and oil was blown out the crankcase breather pipe (the air box is removed so the breather pipe just has a wire gauze “filter” on the end of it) all over the rear of the bike. Anyway, got home, cleaned it all up and drained out some oil to get the correct level on the sight glass.

Now here is the mystery, I check the oil level; all good and go for a ride. Later when the motor is completely cold I check the level, it is so low there is nothing showing in the sight glass window, so top it up to the correct level. Have another ride and later when the motor is completely cold I check the level, it is so high that I need to drain some out to get it back down.
This cycle has just repeated over the last few days; drained out some oil to get it to the correct level, all good. Have my ride, get back and the oil level is good. But when the motor is completely cold (like the next day) there is no oil seen in the sight glass. No leak either.
What’s going on here?
Cheers,
Fraser.

One theory. Gasoline in your oil.

Does the oil smell like gasoline? Hows your mileage? If your float needle in the carb gets stuck, the carb will overflow and drain into your cylinders, and right past your rings into the crankcase. You won't get this while riding, but you will get this when its sitting for a day or so. Your crankcase may be filling up with gasoline. Its happened to me before.

If this is the case, change the oil, but the filter will probably be fine, as there won't be much gas in there (relatively) Of course, find out why the needle isn't seating. any residual gasoline will evaporate out when you go for a longer ride.

Cheers,

Yep,
That's the one. Had the body panels off when starting and petrol sprayed out the crank case breather hose. Guess petrol got in there via a carb problem.
Then remembered that a while back a carb float was sticking open and this caused petrol to run out an overflow hose. Couldn't see why the float was sticking, so swaped it with the other carb and the problem disapeared. Only it didn't, looks like the petrol went through the carb and into the cylinder, then crankcase.

Oh well, the weather's been crap here so at least I will not be missing out on riding while I get this sorted.
Cheers,

Fraser.

Hi Fraser, reading this thread reminded me of an exactly the same problem i had with an electric start Norton Commando i had many moons ago, only the carb's were Amal mk 2's; the theory was exactly the same - stuck needle - fuel drained into cylinder but 'pooled' rather than leaking past rings, when i hit the starter the other cylinder fired resulting in 'hydraulic lock' in the other and the net result was a bent con rod with ruined main bearings and a cracked crank case + lots of £££££££
I don't want to frighten you but ................ good luck jon

It all depends on the luck of where the intake valves are at the time you parked it, and if your valves do seat well.
In the case of the Norton, I would say that your valves seated very well, and you had an intake manifold full of gas. The engine had one rotation to build up enough speed to create that damage, and that charge of gas didn't get into the cylinder until the valve opened and sucked all in.
Cheers,

Yes - you are absolutely right about the engine condition, the Norton had had a full Hemmings rebuild (also supplied offending carb's) about 800 miles before this incident!! which made me all the sicker and poorer at the time!! nice bike though - wish i still had it - YMG 595T where are you??
Also Red 750 Paso (not perfect) on ebay Australia up to $5000 AUD at moment with 12 bids, at least the Ozzies know and value a good bike when they see one.
Cheers jon