Carrillo rods

[embee]

Originally Posted by Alpinestarhero

How do you look for the signs of such stres you describe? Is it clearly visible under a microscope?

Fatigue failures of bolts or other components are often quite obvious, but it's after the event. Crack testing can sometimes pick up incipient failures but with things like rod bolts the start of a fatigue crack might well be too small to be detected. Bolts are usually replaced after a couple of re-tightenings.

Typical crank failures will look like this, pretty obvious fatigue signs.


The failure will have started at the fillet rad on the inner corner of the pin, and the "tide" marks as the crack progressed are clear (in this case the surface has darkened which can be from fretting and/or a corrosion mechanism). Eventually the last part of the web reached a point where the stress was just too much for the remaining material and it broke suddenly.

It can also start at oil hole which has very sharp edge from casting.
Or in rod case bolt can be strong but material around bolt hole not sufficient.

Here is crank that broke right where thread in hole ends.

Here is the one that broke right on oil hole, this one was lightened by falicon and cryo treated. Those H carrillo's had no damage and were used again.