And JRE responded
And JRE takes the prize on this one. Finally got around to pulling the valve cover and sprocket cover. Rear sprocket had come completely undone and the dowel had backed out to the sprocket cover, and the woodruff key had sheared. The thing was wobbling all over the place. I'm amazed that I got any compression at all on cyl 3.
The thing I'm wondering is how this happened in the first place. Since I've had the monster (2 years) it's been really well-cared for. Plenty of oil and coolant...etc. One weird thing - I found broken pieces of a timing chain tensioner inside the upper sprocket cover, but the tenisoners themselves appear fine. I wonder if maybe somebody replaced the tensioners at some point and rebuilt the head, but didn't torque the sprocket properly...? Freaky.
Anyway, next weekend I get to see how bad the valves look.