wondering what would have caused this

[gearhead]

wow i always clean those holes out with compressed air and brake clean until I see the bottom where the hole stops. Even oil left in the hole can lead to hydro locking and either stops torquing or can rip threads out or break the bolt. I have seen this when torquing the rocker shafts down if there is oil in there it can stop it and will not get the shaft tight or it snaps the bolt. I have seen people put the head bolts in the wrong position in cat and put two washers to get it to torque right (there's your sign fool). Messed up threads in the block when I took the bolts out because at the end of the bolt the threads where smashed when the bolt bottomed out in the block. I had to repair threads with a kit from caterpillar and it was not a cheap repair. The holes had to be drilled to bigger size rethreaded and helicoiled.