427 broken valve spring

[RET_COP]

while I agree with pulling the heads off, My thought would first be to boroscope it. You would most likely see shiny marks on the pistons and pressurize the cylinder and listen for air leaks through the intake and the exhaust, that may be enough.

[pgermond]

Had the same thing happen with 12,000 mi on the motor. After another 500 mi another one went. Pulled the heads and replaced all 16. Since that time I have had the whole motor refreshed (rebuilt).

It's a *****, but $hit happens.