What would cause such a thing?

[aengineguy]

Been wondering this for a long time. About 30 years ago I had a 71 RR with a 340 PG 4 speed. It started missing a little, so did a compression check and it was down on one cylinder. Long story short, had to tear it down and pulled the piston out of the dead cylinder and the top ring came out in about 20 pieces. Could it have been detonation? I never heard any pinging, but the RR was used when I purchased.

 

[68gtxman]

Yes. I bought an old 340 and when I tore it down, 7 of the cylinders had one broken ring and the 8th had both rings broken. Probably due to detonation, but possibly broke on initial installation too. It all depends on when the compression loss started, either immediately or after being run for a while.

Did you run regular gas in it or high test?

 

[aengineguy]

Yes. I bought an old 340 and when I tore it down, 7 of the cylinders had one broken ring and the 8th had both rings broken. Probably due to detonation, but possibly broke on initial installation too. It all depends on when the compression loss started, either immediately or after being run for a while.

Did you run regular gas in it or high test?

Pretty sure I was running regular, young family, money tight, stupid me, yadayada. Ran that car for about 4 months before it did it.

 

[68gtxman]

Pretty sure I was running regular, young family, money tight, stupid me, yadayada. Ran that car for about 4 months before it did it.

That was probably the cause. You can't always hear pinging, that's why they install knock sensors in computer controlled engines.

Though you could have retarded the timing to prevent it, if you only knew.