Update:

I worked on it some more and listened carefully with my super custom sounding rod and I've determined that it's for sure coming from the center of the head, and it's a valve noise. I've nailed the general area down for sure, and I'm basing valve noise on the fact that the ticking sounds like it happens half as fast as the engine revs. As in at 4K RPM, it sounds like 2000 ticks per minute. So. The verdict may be a new engine head. I'm pretty sure the bottom end is solid.

Unfortunately, engine heads appear to make up roughly half of the cost of the motor if eBay is to be believed... So I may just get a new motor and sell what I don't need. Here's to a slowly-becoming-absurdly-expensive old skool CBR600!

If only F3 heads were F2 heads... I have one.

 

The story goes like this. I'll put my findings in the form of a parable: Long ago, there was a cricket and a grasshopper. Both knew they needed to store up food for winter. Before they could move on that notion, they were both killed in freak accidents.

Ok screw the parable. Here's where the noise was coming from, and why I no longer consider myself the owner of a viable F2.





Lower rod bearing obliterated, Cyl 4. Particles found in sump screen officially ID'd. Failure progressed to advanced wear, and excessive piston displacement resulted in head contact. Estimate up to .5mm in piston play.

Block viable, piston/rod and most likely crank not viable. Haven't dropped the oil pan and pulled the piston yet. I think I trust the head.

 

So after mic-ing the crankpin and such, everything's far out of spec, so the motor comes apart this weekend. Looking like a pricey deal after all the main and rod bearings get replaced. Looking like a multiple-hundred-dollar fix for this motor, won't ride till spring. The upside is I'll be on here all winter helping people. I need a new crank too, of course.