At first, this may look like another rocker arm problem with a destroyed pushrod cup. But this damage was actually caused by the cracked rocker shaft. When the shaft cracked, it allowed extra play in the rocker arm, significantly opening up the lash. And again, notice where the crack appeared-right around a hole drilled for a fastener to attach the system to the cylinder head. When evaluating parts, you should always be on the lookout for areas susceptible to stress cracks.
Apparently, what happened here is excessive lash allowed the pushrod to separate from the pushrod cup in the rocker arm. Because of high valve tension and the high rpm levels a race engine operates at, the pushrod and cup came back together violently. Eventually, it destroyed the cup, and the pushrod slowly walked its way off the rocker body completely. The result is this rocker arm that looks like it is made out of Silly Putty.
Dorton says that often when confronted with a failure like this, the first reaction is simply to request that the part receive a different heat treatment to make it harder. But this can often backfire by making the part more brittle instead of stronger. Instead, Automotive Specialists is looking at different surface coatings as a possible cure.
Broken connecting rods are another area where a failure can come from any number of sources. Here is a good example of determining the failure by eliminating possible causes. Dorton was able to scavenge almost all the pieces from this demolished connecting rod. Notice how the babbit is still in place on the rod bearing. Although the bearing is significantly damaged, the lack of burn marks and the condition of the babbit show us that a proper oiling was not the problem.
Instead, it turns out that a fracture where the big end of the rod meets the rod beam on the left side is the cause of the failure. When the rod broke on the left side, it broke again above the rod bolt and opened up the rod cap.
Finally, here is one last rod/piston combination that has been damaged from lack of oil. This time around, the rod isn't completely blown apart. At first, it looks as though something has been knocked against the rod and piston, but the cause of this damage is actually a burnt bearing.
If the oil pressure is insufficient to protect the rod bearing, the friction created between the bearing's surface and the crank's rod journal will eat away the softer bearing. This creates a lot more clearance between the big end of the rod and the rod journal, which allows the rod to start bouncing around on the crank. On race engines where the piston is very close to the deck of the block at TDC, this extra clearance usually will also allow the piston to bang into the cylinder head. It is this contact between the top of the piston and the cylinder head that has caused the damage you see here. It is a testament to the quality of this Carrillo rod that it is only bent and not broken. The broken skirt on the piston is a result of the shock wave traveling down from the top of the piston when it slaps the cylinder head.
Unlike the last broken rod, this failure obviously came from a serious lack of oil. In this situation, the engine was so oil starved that the rod bearing is completely burned away, and the housing bore of the big end of the rod looks like charred wood. Dorton says the real cause of this failure was an oil feed line that had gotten against an exhaust header and was sucked shut from the heat. Another common reason for oil starvation problems is a loose oil-line fitting that allows air bubbles into the system.
This example is an extreme case, but it does illustrate one way of determining a difference between an oil starvation problem and oil that is simply too thin for the application. If the oil is too thin, it usually will lead to a failure in the most abused areas while still working adequately in others. For example, if oiling problems have led to a spun rod bearing but the wristpins still look in reasonably good condition, that is a sign that your oil is too thin.