Why would a crankshaft keeper pin shear off?

Thank you for responding. Yes it is the woodruff key. It only sticks into the timing gear on the crankshaft about 1/4". The engine did not hydrolock - no water in the cylinders. When the pin sheared, the timing chain stopped movement, which caused a back fire, which blew a 6" hole in the back of the plastic intake manifold. My question is what else could cause the woodruff key to shear - ie. sticky valves, oil pump... Note that when the pin was replaced, the timing system worked properly with normal compression in all cylinders. A timing chain parts vendor implied that these pins often shear for no reason. What is your opinion?

That is definately a new problem I have never heard of. What I have questions about is that both Alldata and Mitchell say that it is an interference engine. With the woodruff key breaking the valve timing would definately be out of sequence. Consider yourself very,very fortunate that no valves were bent. Make sure you have 170 to 225 PSI for compression. That is factory specs. Good luck, Jim

Thank you again! This engine has 100,000 miles on it and we do not believe that it is an interference engine. We did a cold engine compression test. 1 cylinder was 130, 2 were 135, and 3 were 150. We are hoping the lower compression is just due to the age of the engine. We really appreciate your input!!! We wish you and your family a Merry Christmas.