Valve Timing
The camshaft controls the opening and closing of the engine’s valves. It is synchronized with the engine by a long chain or fiber belt that is driven by and timed to the engine’s crankshaft. Both methods of camshaft drive must be properly guided and tensioned so that timing is stable and that the chain or belt is unable to jump sprockets causing faulty camshaft timing.
Both camshaft drive methods use guides which employ mechanical or hydraulic tensioners. These camshaft drive mechanisms are normally reliable and often provide hundreds of thousands of miles of dependable use. The belt or chain is stabilized and tensioned by guides that are often made of plastic. Occasionally, through many engine heat cycles, the plastic embrittles or the tensioner fails allowing the chain or belt to develop slack which drastically changes cam timing leading to poor running. The chain or belt may jump drive sprockets causing noise and sometimes damage to valves.
Many shops don’t bother to diagnose such problems, but simply recommend engine replacement. Automotive Service and Repair (ASR} can quickly diagnose camshaft drive and valve timing problems. In many cases, we can rectify the failed parts inside the timing case, thereby adding hundreds of thousands of useful miles to the life of the vehicle. So, if you have experienced such an engine problem, and have been told you need a new engine, ASR may be able to save money and time with a reliable, guaranteed repair without an engine replacement.
Most modern vehicles use variable valve timing: an electronic and hydraulic system controlled by the engine control module (ECM). Depending on engine speed, load, throttle position and other factors, the ECM uses mathematical algorithms to advance or retard the opening and closing of valves to fill the cylinders as completely as possible under any operating condition. This process improves power, fuel mileage and reduces emissions.
The ECM controls solenoid valves that regulate engine oil pressure used to advance or retard camshaft timing. The most common issue in this system is the solenoid valves that, like all electrical coils, sometime fail. When this happens, the camshaft timing will be set to a default value that will allow the vehicle to be driven, though at reduced efficiency. The check engine light will be illuminated. ASR can diagnose this kind of problem using an on-board diagnostic scan tool to locate the problem solenoid valve. The part is relatively easy to access and replace.
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