Inside your engine is a set of valves that open and close inside the combustion chamber. This is what allows fresh fuel and air to enter the chamber and the spent gases to escape into the exhaust. When everything is working well, these operations occur a few thousand times a minute. When something goes wrong, your engine will not run very well, and in the case of “interference” engines, the entire engine can lock up. Most modern engines use a timing belt to manage the operation of the valves , keeping the camshaft(s) in sync with the crankshaft. This belt is a wear item and must be replaced in a timely manner to ensure proper engine operation.
Engine Type Matters
There are two kinds of engines- interference and non-interference. A non-interference engine is one where the valves in the cylinder head have sufficient clearance to the pistons when the valves are fully open and the piston is at top dead center. If the belt slips, stretches, or breaks, these engines do not run the risk of permanent damage from valve to piston contact.
Interference engines on the other hand, do not have adequate clearance with the valve is open and the piston is at top dead center, meaning that if the belt has an issue, the piston can touch the valve. This can lead to permanent engine damage including bent valves, damaged heads, and broken pistons. Interference engines are not bad or faulty, this is simply a matter of function. Because of this, timing belts must be changed at regular intervals, typically between every 60k- 100k miles, depending on manufacturer.
The timing belt may also drive the water pump. More than half of all engines that have timing belts (some use timing chains, which are not the same) also use the belt to drive the water pump. This is mostly due to the location of the belt to the pump. Because of this, anytime you replace one, you should replace the other. There are certainly a few exceptions, such as a recently replaced belt or pump and you did not replace the other, but in most cases, you should replace them all at the same time. The belt tensioner and related pulleys should be replaced as well.
To make things easy, NAPA Auto Parts sells complete timing component kits for vehicles with timing belt-driven water pumps. The components include the timing belt, water pump, seals and gaskets, pulleys, and tensioners. Also included are the instructions and a sticker for you to note the date and mileage of the replacement. You may be thinking “why do I need to replace the pulleys and tensioner if they are still good? The answer is because these items have sealed bearings inside them. That means that they cannot be serviced with grease. Eventually, the grease will wear out and in the case of the tensioner, the elastomer inside the unit that provides the tension wears out, leaving you with a loose belt and if the bearings seize, an overheated engine.
What’s In a Timing Belt Kit?
The timing belt itself is a reinforced rubber belt, where Kevlar or fiberglass fibers are used to give the belt strength and resist stretching. Most timing belts are cogged, meaning they have teeth on the inside of the belt that ride in matching teeth on the drive and driven pulleys. The cogs maintain positive connection to the pulleys so that the belt cannot slip. High-performance belts may be made from Highly Saturated Nitrile, or “HSN”, these are more resistant to heat. All belts are susceptible to damage from leaky oil, water, and antifreeze, so if your pump is leaking, then you need to replace the entire system as soon as possible to avoid a failure.
The water pump in most engines where the pump is driven by the timing belt are modular, meaning the pump itself is mounted into a separate housing that stays on the engine. These pumps are more affordable and easy to replace. The pump has a set of sealed bearings and an impeller wheel that moves the coolant through the cooling system. Most pumps now use composite impellers (plastic, fiberglass, etc), which are not susceptible to rust, but they can be damaged by debris. The bearings are the main failure point for these pumps, and replacement is the only option.
Some pumps use paper or metal gaskets, while others use O-rings. Always replace the gaskets when installing a new water pump.
Not all engines require a pulley replacement, but if the related pulley is an idler type (meaning it is not mounted to a driven component) then it will have a bearing. These pulleys will be replaced when performing a timing belt replacement.
All drive belts have to be tight in order to operate correctly. In modern vehicles this is done with a tensioner pulley. This pulley is not mounted to a driven component, it is free-standing with sealed bearings. The other function is an internal spring or elastomer that pushes on the belt, either inward or outward, depending on the configuration of the engine. The tensioner can fail in two ways: bad bearings or worn out elastomer. Either way, if one fails, you will have a bad situation on your hands.
With the proper parts, your engine will last for many years, but if you skip replacing the other components, you run a very real risk of serious engine damage. Besides, the average labor charge to replace a timing belt is $500-$1,000, while the parts are often far cheaper. The technician will already have the vehicle dismantled to access the belt, why waste the labor when those parts are already accessible? They will have to be replaced eventually, it is a good idea to go ahead and do it all at once. You very may well regret it if you don’t.
Check out all the timing belt and water pump replacement kits available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on timing belt and water pump replacement kits, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photo courtesy of Wikimedia Commons.
The post What’s In A Timing Belt and Water Pump Replacement Kit? appeared first on NAPA Know How Blog.