I don't have experience with a 4-stroke trimmer,but I can tell you,that, even if it's still running,when you turn it upside down,and owner's manual says not to do it,and it keeps running;it doesn't mean that it's not getting damaged................Look at the older Ford V-8s;when they spin a rod bearing,they keep running,even though the crank gets all ground up....but it kept runnung,.and you can drive them about 30 MPH,but you made it home............................a little extreme ,but I think you get the point...........some part of the engine won't get lubed,and you'll run into problems in the future.................