My guess is that these cracks beginAugust 15 2013 at 10:29 AM
Fordmech (Login F0rdmech)
from IP address 126.96.36.199
Response to Count me in for one of each
as fatigue cracks that start very small and eventually grow deeper and longer and eventually compromise the cylinder. Ultimate failure of the cylinder may be accompanied by some catastrophic "event" such as a dropped valve that might window the cylinder but in many cases the crack may just slowly reach a depth and length such that it opens up and you don't get a windowing of the cylinder. The primary loads on the cylinder are the cyclic hoop stress due to pressure variation in the firing cylinder and the cyclic thrust side load due to the piston skirt. There are also thermal and vibration related loads. It appears from the pics the failure is situated in the thrust side skirt area. The fatigue crack is not a single event in time but a manifestation of growth (reduction of area) over a long time due to high cyclic stress until failure occurs. The cylinder thickness is the primary factor that determines the stress level in the cylinder wall. Thinner cylinder, higher stress. The higher the stress level the more likely a fatigue crack may start and grow. Once it starts it's a death sentence in time if the cyclic stress/growth continues. The cylinder roughness and corrosion pitting in the water jacket can be contributing factors in the start of fatigue cracks. The age of these blocks is not helpful. Eventually they will all be scrap iron.