Ok,so we have a 08 yz450.My son rides it and last fall he had a "get off" and broke his arm.the bike has sat for aout 4 months.last week he got the ok to ride again so I start getting it ready,I start the bike to warm the oil to change after no more than 20 sec's he comes running out sayin he had draind the oil!!So we put the correct amount of oil in it and started it up with no problems.however after letting it run for a min or so and waiting another few mins to check it there was no oil on the dip stick!started it back up and loosend the "oil pres check bolt" and it is pumping out of there.I then drained the oil and got back 1.1 liters.Did the whole process again with the same results. No matter what I do I can not get oil on the dip stick! I did put a piston in it before the fall but in the 20 min's of riding before the fall everything was fine! I am stuck on this one,any ideas?