How does this happen?

[AutoRb]

Ok guys another problem......

Last week I was driving around the block and all of a sudden i heard a loud a** pop and my car died. Pulled over then I tried to turn it back on and all it would do was crank. Pushed it home, sat for about a week til I could tear into it. Took off the top timing cover and found my timing belt half eaten. So i thought, hmmmm maybe timing belt jump or something. Then I thought it could be my CAS. Looked online for symptoms of a faulty CAS and sure enough I found a thread about a guy saying he had the same loud pop and it was his CAS. So today I was tearing into the Rb again to try to replace the timing belt cause it needs one regardless. I started spinning the crank manually and noticed the exhaust cam gear was slightly bent. I was like "wtf, maybe that's why my belt is chewed" Took off the valve cover to have a better look, spun the crank again and saw the gear spinning but the actual cam was not..... Then took off the the CAS bracket and the gear came with it..... The cam gear completly snapped off the cam.

So i now see why my car died. Cam no spin CAS, CAS no send signal to ecu, Car dies.

Now my question is how does that just break off? and could I have possilbly bent a valve or something?

[Darius]

A dying CAS shouldn't result in snapped cams especially if you are just driving around the block. Sounds to me like the tensioner or idler failed on the timing belt and it started wearing/stretching the belt. It may have skipped several teeth, the valves made contact with the pistons, and boom goes the dynamite.

[Shocker]

One of two things happened here..

Something seized up in the valve train, either due to motor jumping time and valves smashing pistons thus causing the cam to perhaps be fighting a lifter/valve and putting stress into the cam while the belt is still trying to turn over due to the crank dragging it along, and it found a shear point and snapped it.

Or the cam might have had a hair line crack or some type of stress riser in the steel casting itself in that area and it finally let loose… I find this theory doubtful; the porosity in the cam casting is next to nothing. (the voids between steel really do not exist, it’s a very good casting) Camshafts are very hard material so they do not wear easy.. that makes them brittle. (they do not like to flex or twist, they are very rigid pieces of steel)

Who did the timing belt? I know if you actually have TOO much tension in the belt it will tend to want to ride off the cam gears. What does your belt look like?