Porsche has not published any periodic inspection or maintenance requirements for the Variocam. Consequently even cars with a full Porsche main dealer service history may suffer undetected excessive wear or even catastrophic failures. Due to the apparent lack of detailed information on Variocam operation from Porsche, the following section is based on the authors’ understanding, derived from various articles and personal observations. Cross Section Through Variocam Assembly, The diagram above shows a cross-section through the Variocam. The actuation mechanism comprises a housing that is bolted to the engine. The housing incorporates separate moving upper and lower tensioner pistons, each having a plastic rubbing pad that acts directly onto the upper and lower chain runs. The distance between the upper and lower tensioner pads is maintained by an internal spring, supplemented by constant engine oil pressure when the engine is running. This spring and oil pressure maintains correct chain tension, in a similar fashion to the earlier 944 series cars. Possible Causes of Variocam Failure : Aging of the plastic pads (rails). With time and miles, the pads became much more brittle than when new, leading to an increased chance of breakage, and in any case to an increased rate of wear. In failed 968 Variocams, the pads appear very worn with deep tracks, or partially broken, or brittle with some “craters” on them, meaning the material has lost its original properties. Camshaft slope. To support the timing advance, the slope is “aggressive”, that is has an elongated form, to open the valves very quickly. This means additional stress on chain, and when the chain gets stretched, a “hammering” effect on sprocket teeth, particularly at high RPM. Step by step Inspection procedure. Suggested maintenance schedule.
Tags : engine oil pressure, sprocket teeth, chain tension, porsche 968, series cars, internal spring, catastrophic failures, timing advance, maintenance schedule, excessive wear, personal observations, apparent lack, maintenance requirements, service history, camshaft
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