Hey man we've all been there at one time or another...
There is no real way to tell how much damage was done without pulling the engine down and inspecting the internals.
If the engine is running/sounding fine after a top-up then I would just forget about it. No doubt that running the engine without oil will do some damage, but genereally not too much if things didn't get too hot.
Honestly, you would be surprised how long and how hard an engine will run with the oil drained - I've done several "experiments" and I was really surprised.
Next time you change the oil, check for metallic fragments in the oil, if there is a lot then you might have something to worry about.
Otherwise, don't worry too much about it because these little engines will take a lot more abuse than you think!!
My tip: whenever you change oil and/or filter, run the bike at idle for a few minutes, warm it up and check everything for leaks BEFORE riding it.
YOU DON"T want to find out your oil filter is blowing out oil whilst you're halfway through a fast left-hander...
Shiny side up!
ok let the bashing begin but here goes my story....after needing an oil change a good 3 months ago i decided i would do my first ever oil change on anything to the bike at my buddy's garage. i bought the oil and filter from an actual motorcycle shop so i was positive i got the right weight oil and the correct filter. i've watched plenty of changes first hand and i followed the steps to the letter. after completing the job i sit around and bull-shitted with the guys for an hour or so and started the bike so the new oil could cycle thru the engine for bout 5 minutes and then shut it off. about another 30 minutes later i hopped on the bike and headed out for my 45 minute ride thru nothing but country roads home...BIG MISTAKE! i don't have a cell phone and it was now about 230-3am and only about half way home and out in the middle of B.F.E.! all of a sudden my leg feels like i rode thru a 150 degree puddle and it and my bike (including a brand new rear tire)is covered in oil! i turn the bike off go over everything with my dim ass ipod light. nothing from the drain bolt, nothing from the right side, but the whole left side is drenched starting at the oil filter. so with no other resort and not knowing how much oil is left i started the bike up to lslowly limp it to the next gas station about 3 miles down the road. after fighting it in first gear for only a mile or so bike completely shuts off. is this a safety feature the bike has or what? anyways i get the bike to the gas station and early the next morning in the car and get 3 more quarts of oil in it and she starts right up. so i take the rest of my 20 minute ride home on the bike and it seems to hold the oil and runs fine. i get home turn it off to get some stuff for the carwash and head that way to clean off all the oil. not even 6 houses down the block and it sprays another 3 quarts out on my leg! come to find out the seal on the oil filter has completely busted and 9 quarts of oil and 2 oil filters later the bike seems to be running fine. however, i want to know if i caused any damage to the engine running the bike those few miles with low or no oil. how would i go about doing that, or would i be able to tell without running some kind of diagnostic tool? i mean it seems to be back to normal now but i'm by no means any kind of mechanic obviously. anyone have any HELPFUL suggestions?