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.
Modern Volkswagen VR6 and VW & Audi V6 and V8 motors have adjustable cam timing. They have camshafts that rotate in relation to the cam gears using oil pressure and electronically controlled solenoids. This system changes the cam timing for more power or for better mileage while the engine is running. This provides much better overall performance and economy than earlier motors. 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. Timing 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.
Timing Chain Replacement
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 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 system just by replacing the upper tensioner. Most of the other chain type motors can have their upper tensioners replaced in a fraction of the time of replacing the entire system. The job can make the difference between replacing the entire chain system before 200,000 miles and never having to replace more than just the upper tensioner.
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.
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.
Cam Chain Systems
Engines dating back to the 80’s with dual overhead cams had a timing belt that drove the exhaust camshaft, and a cam chain that linked the two cams together to drive the intake camshaft. In the mid 90’s, engines began to use a cam chain tensioner that could vary the timing of the intake camshaft, but had just two position settings for retarded or advanced cam operation. Starting early this century, many camshafts began to have electrically controlled hydraulic systems inside the cam gears to vary the cam position infinitely across a certain range. The belt driven 2.0T engine which started production in 2005.5 incorporates a cam chain with a tensioner and an electrical actuated hydraulic control for the intake camshaft. These features result in an increase in both power and mileage. Failures in these systems are almost always related to insufficient oil changes, and often those clients are just following the manufacturer’s recommendations.