[MOTORHEAD]

FWB:
Got spring specs from Barry R, along with cam and lifters.
Heads r e-brocks, big valves. Local shop did all the spring measuring and set-up. I know they checked for binding, installed height and open/closed pressures, etc,etc.
The adjuster problem was my bad, just adjusted day before, missed re-checking that nut.
Now I had not thought about detonation, but just before the spring broke i was running at 55k rpm and noticed my a/f ratio was at 15-16 :1, so I backed of the gas. 5500r's shouldn't hurt anything, but that lean could have done it.