ALT-4 What is a Timing Belt
Introduction to the Timing Belt
The timing belt, one of several pieces that allow the automotive four-stroke, internal combustion engine to run. Usually found in Over Head Cam (OHC) engines, timing belts and camshaft timing gears allow the valves to stay in time with the crankshaft and the four-stroke cycle of Intake, Compression, Power, and Exhaust (just remember: SUCK, SQUISH, BANG, BLOW). So, how does this work?
The Rubber Meets the Gears-
Depending on what type of camshaft style you have, the timing belt will either be in an oval shape in OHC engines or in a triangle in Double Over Head Cam (DOHC) engines. It is made of a durable rubber and strong thread not that far off from how a bias ply tire is made. It has teeth on the inside (where the gears will touch the belt) and is smooth on the outside. It has these teeth so that the belt doesn't slip and get the entire process out of whack. Remember, this is the only way that the camshafts stay in time with the crankshaft and pistons. If it gets out of sync, nothing good usually happens.
SUCK, SQUISH, BANG, BLOW-
So, what do I mean by "nothing good usually happens?" Engines are built in two types of configurations on top of how many cylinders, DOHC, OHC, OHV (Over Head Valve, AKA: Push Rod Engines), etc. Your engine will be either "interference" or "non-interference," with the former usually what most modern engines are and will have the biggest repair bill. "Interference" engines are designed so that the piston is as close to the valve and/or the valve is open as late as possible. This is good for power, as the longer you have the valve open, the more air and fuel you can allow the engine to ingest. The downside? If your timing belt slips or breaks and the valves are open, the pistons will hit them and result in broken valves, bent valves, valves melded into the pistons or head, or all of those situations at once. All of which, are a very large repair bill. "Non-Interference" engines are quite the opposite, with the valves usually not coming too close to the engine. However, bent and broken valves aren't guaranteed to not happen. Break a valve spring, float a valve, break a connection rod, it can still happen.
To keep the valves in time, the cam gears, which are connected to the camshafts, are used along with the timing belt. Cam gears are half the size of the crankshaft gear. Why is this? Well, during the four-stroke cycle, the valves must be open for the intake and exhaust strokes (the SUCK and the BLOW parts). In order to do this, the camshafts must spin twice as fast as the crankshaft. Remember, just because you have a belt or a chain, this is still gearing. The smaller gears will turn more and faster than the big gear. It's a 2:1 process, two turns of the camshafts for every turn of the crankshaft. If the crankshaft has (for the simplicity of this article) 42 teeth, the camshafts must have 21 gears. Camshafts have their own setups and will be for a later article of their own.
So, you now see why the timing belt is so important and why it needs lots of observation and constant checks the manufacturer's intervals. If you don't, it probably won't just be a broken timing belt you'll have to worry about and pay for. If it does break, check or have the valves and head checked for bent or broken valves. You keep your car well maintained, you shoudn't have a problem with your timing belt.
