Your timing belt should be replaced every 60 to 100 thousand miles. Car makers have specified the replacement intervals for timing belts. In an interference engine, the valves and piston share the same air space. They never touch, unless you’re timing belt breaks or skips and this is a catastrophic failure that requires removing the head and replacing bent valves.
Non-interference engines do not risk this contact if the timing belt goes out. Nonetheless, either can leave you stranded so regular timing belt replacement is very important. Timing belt is a toothed belt that connects the engine crankshaft to the camshaft or so the valves will open and close at the proper time in relation to the position of the pistons. The camshaft rotates at exactly ½ speed of the crankshaft, meaning two revolutions of the crankshaft are equal to one revolution of the camshaft.
When a timing belt breaks, the camshaft stops turning leaving some of the valves in the open position. Because the crankshaft is heavier it continues to rotate by inertia. Also it is automatic reaction to try and start your car when it dies, when the engine cranks over you are turning the crankshaft. In an interference engine, this will cause the pistons to strike the valves that were left open. This may result in broken or bent valves damaging the pistons and possibly destroyed cylinder head. The damage will be less extensive in a non-interference engines but in either case, the engine will stall leaving you stranded.
If you do decide to replace the timing belt yourself. Study the procedure before digging in, either in a service manual or on the internet. On most transverse four-cycle engines, you’ll have to remove the passenger side motor mount in order to gain access to the timing belt. This means the engine powertrain needs to be supported in that area while you are working. Finally getting to the lower portion of multi-piece timing belt covers usually requires underbody access. A fender cover does not hurt either, to protect the paint from your belt buckle and dropped tools. Time and time again we cannot stress this enough. BE CAREFUL. Make sure you know where the timing marks are on your engine, and that you have them set up properly with cylinder # 1 at top dead center (TDC) on the compression stroke before attempting to replace the timing belt.
After you remove the top section of the timing belt cover, you should see a timing mark on the camshaft sprocket.This mark usually lines up with the edge of the cylinder head or valve cover. For the crankshaft below, there probably will be a timing mark on the damper pulley that lines up with another mark on the lower cover.
Or, the service manual may direct you to the transmission end of the engine to look through a hole in the bell housing for a timing mark on the flywheel. The flywheel is bolted to the other (transmission) end of the crankshaft. On some vehicles you may find these marks in all three places.
Support the engine with some sort of skyhook if you need to remove the right side motor mount. Some belts are installed with a mount in their center, making changing them problematic. The tensioner may be an automatic hydraulic type that you simply crank in one direction to remove the old timing belt.
Or you may have to loosen the tensioner pulley adjustment bolt to release the tension and the belt. Before proceeding, confirm which way the engine rotates during normal operation. Knowing which way the engine turns is important for checking the new belts alignment later. You don’t want to be off by a tooth on one of the sprockets. Don’t rotate the engine backward to the marks. Crank it around forward to maintain the correct tension and to keep the belt from jumping teeth.
TDC? Now you can carefully slide the old timing belt off its sprockets and pulleys, while trying to keep the camshaft and crankshaft from spinning. With all the timing marks lined up, route the new belt around the largest diameters first, leaving the smallest pulley or sprocket for last. Now, make sure the timing marks are still lined up.
If you’re working with a manual pulley setup, now is when you perform the factory procedure to tighten the new belt. A hydraulic tensioner takes care of this for you. Once the tension’s set, place a socket on the big nut holding the front pulley on and use it to turn the engine over- to complete crankshaft revolutions in the direction of normal rotation. Line up all the timing marks again. Everything still on the money? Then you’ve finished replacing the timing belt, but you have another hour’s work to reinstall the cam belt covers, any shrouding and all the wires, engine accessories and hoses you moved or removed.
WARNING: If you know you’re working on an interference engine, do not rotate the camshaft or the crankshaft independently while the timing belt is off the engine. You could cause the pistons to hit the valves, or vice versa and cause the same damage as of the timing belt had snapped with the engine running, bent valves.
NOTE: while you have the timing belt off, you can inspect other component’s, like the water pump, front engine oil seals. It is best to replace these parts while you have the timing belt off.