Timing belt and timing chain replacement at your home in Kansas City, Kansas

Inside the engine, the crankshaft turns as the pistons go up and down. Up in the head, the camshaft opens and closes the valves that let air in and exhaust out. Those two have to stay in step with each other, down to a fraction of a turn. The timing belt or timing chain is what ties them together.

You usually can't see it. It sits at the front of the engine behind covers, and on a chain engine it runs inside the engine itself. The belt you can see on top, the long ribbed one that turns the alternator, is the serpentine belt. That is a different part and a much smaller job.

A timing belt is rubber with teeth on the inside. On most engines it runs dry, outside the oil, and it wears out with age and miles. Car makers give it a replacement interval, and your owner's manual lists it. A belt that goes past that point can look fine and still snap.

A timing chain is metal and runs in engine oil. It is meant to last much longer, often the life of the engine when the oil gets changed on time. But chains stretch, and the guides and tensioner that hold them in place wear. Skipped oil changes speed that up a lot.

If you aren't sure which your car has, check the owner's manual or text Josh the year, make, model and engine size. He will tell you.

On a lot of engines the valves and the pistons share the same space, just at different moments. Mechanics call these interference engines. As long as the timing is right, they never touch. When the timing belt snaps, the camshaft stops but the crankshaft keeps spinning for a moment, and the pistons can slam into open valves. That bends valves and can do worse.

On other engines there is room for both, and a snapped belt just shuts the engine off and leaves you on the side of the road. Either way you are stuck. But on an interference engine, a belt that was due for replacement can turn into a much bigger repair. That is why the interval in the manual is worth taking seriously.

Chains usually give some warning before they fail. Belts often give less. These are the things to listen and look for.

• A rattle from the front of the engine for a few seconds right after a cold start
• A check engine light, since a stretched chain can throw the camshaft and crankshaft out of step and the computer notices
• Rough running or a stumble that wasn't there before
• Metal flakes on the oil drain plug or in the oil
• On a belt engine, a tick or slap at the front, or oil seeping onto the belt from a seal behind it

Getting to the timing belt or chain means taking a fair amount apart at the front of the engine. While it is open, the tensioner and the idler pulleys that guide the belt or chain are right there. They wear along with it, and a worn tensioner or a pulley with a bad bearing can take out a brand-new belt. Josh looks at them and tells you what he sees before he puts it back together.

On many engines the water pump also sits back behind the timing cover. That is something to talk through with Josh when he quotes the job.

Some timing jobs fit easily in a driveway. Some engines are packed so tight that the job is long and fussy, and a few are better done with a lift. Give Josh the year, make, model and engine and he will tell you which kind yours is.

Call or text Josh with the year, make, model and engine, and the miles on it. If the chain is rattling, a short video of a cold start helps a lot. You get a clear quote before any work starts, and then Josh comes to your house to do it.