i was draining the primary oil out of a 75 sportster and about 1 1/2 quarts of oil came out from the primary drain plug and there was hardly any oil in the oil tank itself. Where could all this oil come from? could it be the primary crankcase seal?

 

Yes, it could be and it may be from the Crankcase seal being faulty.

 

thanks. is that the only place it could be coming from?

 

Well, the empty or near empty oil tank could just be because the bike has a leaking or bad ball check valve in the oil line. What happens with that is if left for a time, the oil will, because of gravity, seep down into the motor. Once the motor is started up and running, it will pump the oil back up into the oil tank again. It is not a problem per se, but more of a nuisance kind of thing. It won’t hurt the motor, although it can make the motor hard to start. If the ball check valve is leaking and all of the oil in the oil tank leaked down into the motor and the crankcase seal is bad or leaking then that could well be where all of the extra oil came from. It also could be because the primary case was over filled to begin with too! Other than that, I can't think of any place else that the oil could have come from. Good luck with your bike and ride safe!