I bought my 450 in late April and have rode it off and on thru the summer. It is time to replace the stock rear tire, but I am wondering if I need to replace the top end? I have replaced two stroke top ends which I could do in my sleep, but a 4stroke ? If I do need a top end change is it very difficult to do and do I need any special advice or tools? I want to keep this bike in mint condition, so when I ride hard there won't be any failures. Anybody got any suggestions?