42 226 six cylinder knock

[edhd58]

Well the old gal developed a knock last fall. I decided to tear her down this spring before something terrible happened.
The knock was pretty bad when the motor was cold and almost went away as it warmed up. It was still there under acceleration.
All the "running" sounds and diagnostics was telling me and others that heard it, that I had a rod knock.
I got it torn down to pistons out today and all the rod bearing and journals all look good, and the wrist pins were smooth with no play.
However as the pics show number 5 and 6 cylinders are scored. Number 5 is the one that sounded most like rod knock. It looks more like piston skirt material has transferred to the cylinder walls. Now to get it to a machine shop to see what happens next. I just wonder what happened to cause this.
I do know the motor did get hot enough once to percolate. I found a vacuum leak at the vacuum brake connection on the intake and was told that a vacuum leak will cause one to run hot.
All the damage is on the valves side of the motor.