I blew out the base gasket on my '95 XR650L a few days ago and finally got the time to take apart the top-end... Problem confirmed! I'm at least the third owner of this bike and the guy who I bought it from mentioned that had been rebuilt. The rebuild job was amateur and done in a rush... So far I found one sheared valve cover bolt: And a missing dowel pin down where the cylinder and crankcase meet. What I need to know is...it is possible (but unlikely) that the dowel pin was in place when I removed the cylinder and it is possible that the dowel dropped into either the cam chain hole or the crankshaft hole while I was removing the cylinder. That said...just how much room is there in the works if this indeed happened? I fished around with a magnet and didn't find anything and I also spun the crankshaft around a bunch of times and everything feels smooth. If something the size of a dowel pin had dropped into either hole wouldn't it be big enough to catch on something? The last thing I want to do is put it back together and have it self destruct due to an errant dowel pin. I was hoping this would be a relatively quick repair. I really don't want to split the case... I think the best option may be to tip the engine upside down and give it a few firm shakes...tough to do at the moment given what's left of the engine is still in the frame. The cylinder, head, valve cover, camshaft, and piston all went to my local engine shop, I'll get them back in a few days. He determined that the base gasket failed because whoever installed the cylinder did NOT follow the correct torqueing sequence and/or overtorqued the bolts, thus the base warped. It will have to be machined to get it back to spec. Same story on the head, it's warped too but not as badly. Sigh...if you are going to the trouble of doing an engine rebuild at least do it properly! Argh!