Oil Overflow

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Sep 19, 2005
Before starting my newly acquired 850 Commando for the first time in over a decade, I put three quarts of oil in the empty oil tank. It was a little over the full mark on the dipstick but I wasn't going anywhere and there is no aif filter yet to foul if a little blew out. After two minutes of running, I was surprised to find what looks like over half a quart pumped out on the floor. Was this caused by overfilling the tank or is something more serious going on? The oil level is still at the top of the tank, higher than before I started it, after leaking oil like the Exxon Valdez. Could there have been old oil in the sump that has now been pumped out? Any suggestions on why I appear to have more oil than when I started?
Did you check for oil in your sump? My entire tank will drain into my sump in a week. Add the oil you added to the tank to the oil in your sump and the total would exceed the tank capacity!!
The engine is a dry sump configuration, unlike most cars, hence the external oil tank. The oil pump is a two-part pump. The high-pressure side sends oil from the tank to all the places that need it. The scavenge side sucks all the oil that makes its way down to the crankcase back into the tank.

As the pumps get a bit worn, and the bike sits for a while, gravity drains the tank into the crankcase through the worn clearances. You look in the tank and think "my goodness, it's empty", so you fill it. When you start the engine, the scavenge pump, which has about 50 percent more flow rate than the pressure pump, picks up all the oil that leaked into the crankcase and puts it back in the tank, much faster than the pressure pump is sending it out again. This is what causes the overflow.

It happened to me when I was at N-V with the works hack 650SS I rode home. Got quart of oil all over my shoes! I've remembered ever since that you run the engine for about 10 minutes before you top up the oil tank. The measuring stick is calibrated for hot oil anyway.

See what we meant? You knew right away what was wrong....give yourself a pat on the shoulder.......you deserve it. You are becoming "acquainted" with the mechanics of the Norton.... Have no fear...in time, you too will indeed be "Mechanically inclined"!

Good for you!!! :D

Frank...good explanation. Better shoes.... than in front of the rear wheel at the red light on the corner :lol:
Wet Sump Question

I have a 72 Norton 850 which after sitting for a week or so will leak all the oil from the tank into the crankcase. My question is that if you start the engine with the knowledge that its all in the crankcase will it hurt the engine as in a short time the oil should be circulated and the tank refilled. Does this make sense thinking this or should one drain the oil from the sump and put it back in the oil tank prior to starting? Any help or explaination would be appreciated. Semper fi devildog
Yes it will, first the oil in the tank may not be enough to keep the oil pump supplied causing rapid wear of the bigends, second all that oil in the crankcases wants to escape eg out of oil seals, up pistons past rings into combustion chamber. I have done it a couple of times through forgetting before i put a non-return in but I would never knowingly do it.
Crankcase Oil

Thanks for the feedback, yup that is what my symptoms were, bit of smoking around the exhaust, ran it only for a bit, shut it off, then had a bit of oil leak our the points cover. When one takes the oil out of the crankcase, should you remove all of it or just part of it?? Never done it before nor had this problem. I naturally dont have the bike here with me but where is the drain plug at--- directly under the crank? thanks for the info. devildog

Drain it all from the crankcase and pour it back into the tank. Consensus seems to be that the best oil level is just above the "low" mark.
My experiences have shown that if the bike has 'stood' for more than a week or even drained.. , and the oil is indicating low.. I will drop the oil from the crankcase.

My thought is make sure the area around the sump plug is clean and free form ANY dirt or crap.. wash it off. and I use a screen or filter ~ (Actually a workplace hair net ~~ LOL !! to ensure cleanliness ..!!) ~ further ensure or eliminate contamination risk !

PLease ~ be careful refiting the sump plug as it is very possible to snap them off .. leaving the thread and magnet suspended in the sump!!

While it has never happened to me .... I am led to believe that if the engine is fired up with a "belly full " there is a high risk of blowing the seal between the crankcase and the primary drive.. a very unsavoury concept..

(I have only ever seen my first 1966 BSA A65L blow volumes of smoke out the exhaust because of a 'wet sump!)

Ideally ~ after draining ~ I believe that it is advisable to have <200 mil> remaining the sump before start up.

As discussed at length, the ideal mark ( I feel ) is halfway between the full and add marks.

My bike will discharge oil into the base of the air filter once I exceed 4500 rpm, when any higher .

This was endorsed recently after I played silly buggers on a club ride and racked up to <90 mph> jostling with a Hyabushi ! :lol:

The oil level 'set' at the half way mark as suggested , did not change and there was just a little oil dwelling at the base of the air filter.

(I learn the hard way , topping up oil tanks when low and had been standing for some time ~ oil spewing every where !)

As for leaking form the points cover.. I was not sure whether to be amused or shocked to find a <1/8"> hole drilled in the bottom of the points cover.
I can only assume to allow seeping oil to escape the points housing..

Mine still seeps oil into the housing from the engine! I have another seal in the parts box but have not gotten back to that as yet !
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