Has anyone ever had a collet (valve keeper) do this?! Snapped in half! I thought the bike was making a slightly different top end noise & this is what I found. This is the 4th collet failure I've had on my 350/4. The first 3 wore away the ridge that fits in the valve groove (resulting in 2 dropped valves) - this was diagnosed by a mechanic as crappy case-hardening. I got the collets case-hardened & two of the exhaust valves collets then proceeded to wear away (elongate) the valve grooves. I then replaced those collets with the standard Honda ones only to have this happen. Sheesh, this bike is starting to piss me off! I replaced the broken collet (without removing the cylinder head - I'll tell you how if you ask). I then removed the sump - I couldn't find the missing piece but there was a lot of fine crushed metal of the same colour (yep, you're gonna tell me it's bits of bearing, gears, pistons, cams, etc, but the top end looks remarkably clear of damage). I cleaned out the sump & oil strainer, put in new oil, & the bike runs fine. What next?!