OK, I will admit it. I had, what sounds like, the exact same thing. It happened very briefly, within a few minutes of starting it the first time after the valve clearance adjustment.
Same as you. VERY carefull measurements (three times with metric feeler gauge). Used Dinqua's calculator and Moe's spreadsheet, plus my own spreadsheet. 6 out of 8 shims were changed (3 out of tolerance -too loose, 3 on the very edge -2 were on high side, 1 on thin side). New shims were essentially a shim size different. My micrometer measures down to .005 mm and it's digital.
After seating and installing shims/buckets/cams/caps/bolts (liberally oiled all parts with fresh oil), I reassembled and rotated engine by hand several times. Checked clearances, all properly within tolerance. Assembled entire bike, started (up immediately), ran at higer throttle than idle to get oil to flow (oil light not on). Took a very short spin (50yd). During that run (I wasn't being too gentle either) it did have a short lived hammer sound. At first I thought maybe I was in-between gears. I'm still not sure exactly what it might have been.
I have 700 miles on it since the adj. (2003 TA) and the valve train is quieter and gas mileage has improved very slightly. It's running very nicely (totally stock minus AIS). Check done at 12,900 miles, have 13,637 on it today.
New plugs (NGK Iridium DPR8EIX-9), oil, and filter during adj.
What I would NOT do next time, is drain oil before doing the adjustment. I did, and it was three weeks or so by the time I received all the necessary parts to reassemble. I probably spun the motor by hand a dozen or more times and might have pumped out the oil pumps (they must be primed before installation per the manual). However, I never did see the oil pressure lamp come on. So who knows. If a piston wacked a valve, I'd have to believe it'd be all over. I don't know how a valve with a stem at the angle these are, could survive such a strike.
In any event, I did look over the bike. No I did not open it back up. I was confident in the measurements enough to know they wouldn't have changed much (plus new shims were not drastically different). All shims were 'snapped' in to the buckets firmly before re-installing. Everything including all bolts, caps, dowels, etc went back into the same position. All female and male threads were cleaned and oiled and great care was taken not to allow anything drop into lower case.
I did re-check torque on all cap bolts, but next time I will rotate engine to remove tension off left side cylinder and recheck (10Nm).
Jay
