Frankly, the original design of a timing chain was to last for the life of a motor, or at least a quarter million miles. Frankly, many timing chains can accomplish that if properly cared for. The critical factor is oil changes. Timing chain systems have plastic guides and tensioner rails. The contaminants that build up in engine oil eventually attack the plastic, causing softening with rapid wear, or granulation with plastic bits falling off or breaking.
The high failure rate of these internal plastic parts once a vehicle has over 100,000 miles is the crux of our argument that engine oil should be changed every 5000 miles instead of following the factory recommended oil change interval of 10,000 miles. It is mostly true that the metal internal components don’t wear out rapidly given the factory interval. But the plastic parts and turbochargers almost always fail early.
Volkswagen and Audi motors have had cam chains since the first dual overhead cams of the late 1980’s, however they had no tensioners. These systems got adjustable tensioners in the mid 90’s. Then in 2005.5, they changed again to adjustable gears and fixed tensioners.
Gunk deposits from old engine oil can clog up these cam control systems and cause an engine that will barely idle and cannot be driven. These cam chain systems are one of the reasons that synthetic oil is required in most engines from this century. And the best synthetic oils should always be used.
Most timing chain systems are located on the transmission end of the motor, so the transmission must be removed first to replace the chain system. All of these timing chain configurations have upper chain and lower chain sections, meaning many parts are required. Special tools and training are involved to precisely align all the crank, cam and idler gears. Repair times vary from 10 to 32 hours depending on which model and motor. Severe gunk and varnish can add 6 to 12 more hours for disassembly and cleaning.
Each of these timing chain systems has upper and lower hydraulic chain tensioners. On the VR6 engine, the upper tensioner is the only part replaceable without major disassembly. We commonly change the upper tensioner as we almost always find it sticky when compressed. It is a clear bet that we are adding years to the life of the timing chain system just by replacing the upper tensioner. Some of the other chain type motors can have their upper tensioners replaced in a fraction of the time of replacing the entire system.
Some timing chain systems, like the 2.0T made since 2008, are located on the pulley end of the engine, and have a single chain from the crankshaft to both cams. The 2.0T engines of the model years 2008 through 2013 came from the factory with timing chain tensioners with defective designs that have the dire potential of bending all the engine valves when they fail. Motors built as of 09/2013 should have an updated design that is finally reliable. Fortunately, the timing chain cover includes a 2″ rubber plug that can be removed easily to identify whether the tensioner is of an updated design.
Some timing chain systems have an oil control manifold between the camshafts called the cam bridge. In some instances, a screen inside this cam bridge may break apart and cause cam timing failures. Sometimes just removing the screen debris and cleaning out the cam bridge and cam gears may be all a timing chain system needs. Many times however, that coincides with lack of oil changes and age that has also caused wear and the entire system must be replaced.
As one might observe, timing chain replacement is a high dollar investment. Some of the cars that need chain jobs are approaching or over 20 years old. The question must be asked about the relative value of the car versus the repair cost. Each vehicle and each owner is different, and all the variables should be explored before committing to the job or committing the car to the earth.