Anyone know what would cause a keyway to shear off a crankshaft? This happened on my ranger 4.0L last week. 9000 miles ago I had my timing chains, sproket and whatever other parts that would go with this type of job replaced and suddenly the truck just died while taking off in a left turn lane. No noises or signs of anything being wrong prior to this happening. The dealer told me a valve may have dropped on one of the heads and hitting a piston causing this to happen. After it died, going to start the truck it sounded like the starter was just spinning but the crank was turning with it and that was it. Now im sure if a chain breaks that will cause major engine damage which I now have. They said the chains and everything was fine when they took it all apart. Not sure what really happened. Just kinda weird I had the timing chain job done and this happens. Any ideas on really how the keyway sheared off or does this sound legit? In the end I need a new engine and that sucks cuz it's gonna cost alot!!!.....