On any automobile engine, one of the basic engineering challenges is how to transfer the rotating force from the crankshaft to the valve train. This is so that the valves open and close at exactly the correct times relative to the motion of the pistons.
On most older-style engines, this is done by a camshaft just above the crankshaft which is driven by a chain on a cogged gear to keep things in time. One of the drawbacks of that arrangement is its complexity.
In order to open and close the valves, a complicated array of moving parts is required. For each valve, the cam pushes on a lifter which moves a pushrod, which moves a rocker, which moves the valve.
As modern engines increased the number of valves per cylinder for the sake of efficiency, another change was to actuate these valves directly with a camshaft on the cylinder head rather than in the engine block.
There are some designs that use an enclosed chain to drive an overhead camshaft. However, it is much simpler, cheaper, and more common to use a cogged rubber timing belt.
Timing Belt Replacement Costs
Some examples of the timing belt replacement costs for some common vehicles using $100 per hour labor rate are as follows:
- For a 2003 Honda Accord with a 3.0-liter engine, the estimated labor time is around 4.6 hours. A factory replacement belt costs about $104 and a Dayco belt costs about $19. The total job cost would be around $564 using OE parts and about $479 using aftermarket parts.
- For a 2002 Toyota Tacoma with a 3.4-liter engine, the estimated labor time is around 3.3 hours. A factory replacement belt costs about $56 and an ITM costs about $24. The total job cost would be around $386 using OE parts and about $354 using aftermarket parts.
- For a 2005 Volkswagen Passat with a 2.8-liter engine, the estimated labor time is around 4.6 hours. A factory replacement belt costs about $98 and a Continental timing belt price is about $17. The total job cost would be around $558 using OE parts and about $477 using aftermarket parts.
- For a 2005 Dodge Neon with a 2.0-liter engine, the estimated labor time is around 2.7 hours. A factory replacement belt costs about $39 and an ACDelco belt costs about $27. The job cost would be around $309 using OE parts and about $297 using aftermarket parts.
On all of the above vehicles, there is an option of buying an aftermarket belt kit rather than just the belt. The kits typically include the idler pulleys and/or the belt tensioner, and sometimes, the seals.
The average cost of a belt kit is about $50 more than just a belt, and the additional labor for replacing idler pulleys is about half an hour in most cases. This would add around $100 to the cost of a timing belt replacement.
When to Schedule Timing Belt Replacement
Timing belts have a scheduled replacement interval which varies from manufacturer to manufacturer. On a Honda, for example, the timing belt replacement is recommended at 105,000 miles in normal operation, or 60,000 miles if the vehicle is operated in very hot or very cold conditions.
Toyota recommends changing the timing belt at 60,000 miles on some of their engines, and 90,000 miles on other engines. Volkswagen recommends replacing the timing belt between 60,000 and 120,000 miles.
Interference vs Non-Interference Engines
One of the things that makes timing belt replacement more critical or not is whether an engine is an “interference” type. When a valve is fully-open (when it extends into the combustion chamber) and the piston can come fully up without hitting the valve, then, it is a non-interference engine. If the piston can’t come fully up without hitting the valve, it is an interference engine.
On an interference engine, the timing belt keeps the pistons and valves moving in a coordinated fashion. In the event of belt failure, it’s possible for the pistons to hit the valves which typically bends valves and sometimes, damages the face of the piston.
This can, depending on the engine and the amount of damage, cost more to repair than it does to replace the engine. Therefore, on an interference engine, the timing belt maintenance schedule and the other parts involved in a timing belt service are generally taken very seriously.
Whichever type an engine is, the exact alignment of the cams to the crank is necessary for it to run properly. Typically, there are a variety of alignment marks on the timing case or the timing cover, on the cam and crank sprockets, and sometimes, on the belt itself. In many cases, special alignment and holding tools are a part of the timing belt replacement procedure.
Other Things That Are Recommended with Timing Belt Replacement
Given the relatively long interval on timing belt replacements, the large amount of labor involved, and the possibly very expensive consequences of timing belt failure, it is very often the case that other associated parts are replaced as well.
A timing belt has a tensioner and often, one or more idler pulleys. Very often, these are replaced with the belt as if the bearings in either fail before the next scheduled service and the timing belt can fail.
In many cases, the timing belt also runs the water pump. There is no scheduled replacement interval on a water pump, but they are usually difficult to inspect when they reside inside a timing cover. If a water pump fails, that can also cause the timing belt to fail.
It’s a normal recommendation to replace a timing belt-driven water pump at the time of timing belt replacement. Most of the labor overlaps with the belt replacement, so it’s usually only an additional labor charge of about half an hour.
Where the crankshaft and the camshafts project from the engine, they have oil seals to prevent engine oil leaks. To replace any of these seals requires removing the cam and crank gears. Sometimes, it also requires special holding tools, seal installation tools, and more labor.
Unfortunately, it’s not always possible to see a leaking seal before the timing covers and belt are removed. However, the consequences of not replacing a leaking seal are the likelihood of the timing belt having a short life. If replacing the seals is recommended due to a leak, it’s a good idea to have it done, even if it increases the cost and the time the job takes.