Quote:
Originally Posted by jt20
I don't know how many of these heads I've taken off. - not like I've done it for 20 years in a shop though.
Often I have experienced that the bolts have a wide range of "de-torque' values. this is a mixture of the headgasket collapsing and the bolts losing plasticity in that range.
Primarily, the rear passenger bolts on the head will rust due to a failed HG at some point which will not be perceivable by visual inspection or testing of the coolant. this reduces the holding power of the bolts.
Fast forward, you now an have an aluminium head prone to cracking which is held against the block by uneven forces. then add high combustion pressures and heat. . . . well, uneven distribution of forces and internal stresses in the metal seem the most likely candidates for a cracked head, in my humble opinion.
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This seems quite unlikely. When you have bolts that are torqued as factory head bolts are there isn't any sudden, unexpected shift that would cause bolt "plasticity" to be "lost."
The Coefficient of Thermal Expansion differences in materials are already known long before anything makes it to the assembly line. If a failure was going to develop it would be because of a improperly cooled engine or due to lack of maintenance, neither of which I am concerned about on this engine. But those would cause other issues in most engines.