The timing belt is a wondrous thing. Without the timing belt snaking through all those meticulously adjusted tensioners, the engine would just plain refuse to circulate fuel and air into and out of itself. Anything that important, though, has got to have some majestic ways that it can go wrong, and a thrown rod from a high-RPM timing belt failure is one of the truly spectacular tragedies that can befall an engine.
When a timing belt throws a rod
If you've seen the results of a thrown rod, by whatever method of failure, you know that it's no laughing matter. Something so carefully engineered and criminally expensive as an engine block being reduced to scrap by a five-inch-long piece of metal that was once essential to its operation is basically automotive treason.
Luckily for most of us, timing belt failure will only cause your engine to throw a rod under a certain set of circumstances. Whether or not those circumstances come to pass depends mainly on whether you have an interference engine or non-interference engine.
When a timing belt breaks in a non-interference engine -- where the pistons and valves always occupy their own area in the block and don't alternate their presence in the same space -- all you'll need to do is get a new timing kit. Either have the car towed to a shop or pop off the timing cover and install it yourself and you're usually good to go.
In an interference engine, however, a thrown rod is a fairly likely outcome. Proper valve timing is vitally important to an engine where the valves might collide with the piston. There are some circumstances under which damage can be minimized, but we'll cover that later.
Why does it happen?
When a timing belt snaps, the principal casualties are the valves. If the stems break and the valves go ricocheting around in the cylinder, their furious speed will cause them to clatter into the piston and connecting rod with no small amount of destructive power.
Sometimes the piston gives up first, leaving the connecting rod behind to poke around in the empty cylinder until it either disintegrates or jams itself clear through the solid metal wall of the engine. If the rod goes first, the end of it that's still connected to the crankshaft can easily perforate the engine block.
At this point, your engine is toast. Don't even think about putting duct tape over the hole in the block. It's been tried -- multiple layers of it, even -- and even duct tape isn't enough to contain all the scorching hot force that goes on inside a combustion engine. In this case, an ounce of prevention is worth ten tons of attempts at a cure.
How can I prevent a thrown rod?
The key to prevention, just like with almost every uncommon yet catastrophic engine malfunction, is to make sure the belt doesn't break. Keep up with all your recommended maintenance schedules and, if you have the know-how, inspect your timing belt from time to time for signs of wear and tear.
It also never hurts to do some research on the make and model of your vehicle so you can get a good picture of how long your timing belt is expected to last. There are plenty of knowledge resources along those lines on the Internet, and the tried-and-true method of a phone call to the right repair shop is still as effective as ever.
Of course, there are other malfunctions that can cause your engine to throw a rod. In fact, a broken timing belt might actually be the least likely of them all. Catastrophic engine failure isn't fun for anyone, so read up on extra precautions you can take and avoid it in all its forms.