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5 chain engine
crankshaft is connected to the intermediate shaft by a chain. this chain is kept in tension by a chain ramp that is pressed against the chain by a tensioner. this tensioner is static (doesn't move).
the intermediate shaft drives two chains - one to a camshaft on each head. again, there is a chain ramp and tensioner for each chain. again, static.
at the heads, the intake and exhaust cams are joined by a chain. this is a dynamic system, designed such that varying tension on the chain adjusts cam position (the variocam system). a signal is sent to a solenoid that activates an actuator that moves the chain in and out. there are pads on these actuators. these pads wear with time. there is a sensor in the system that measures the deviation between the two cams, which is a sign of pad wear. when deviation exceeds 9 degrees at hot idle you get a cel. deviation should be a steady number and not fluctuating at idle.
failure points
intermediate shaft bearing can fail. this is an interference engine which means that if valves are extended when piston is at top dead center there will be contact and things break. failure of the bearing will cause loss of timing and piston/valve interference. i won't get into mechanisms of failure here (lots of opinions) but, without the guardian device, the only sign of failure is a pre-failure wobble in the bearing that can cause rapid fluctuations in deviation at hot idle.
ramps can fail. this will cause loss of timing and piston/valve interference. mechanism? presume lack of tension from tensioners causes chain to slap and work ramps. there is an updated ramp available from LNE, and updated tensioners from porsche.
sensor or sensor wiring can fail. repair/relace. note that a mis-aligned sensor can produce incorrect readings (ie, read a deviation of -4 when it is actually -2). this is not a big deal, as what you should be monitoring is the change in deviation over time (sign of your pads wearing) and not the actual value.
soleniod or wiring can fail. on later cars the soleniod can be serviced from outside of the engine; on ours you have to open it up. typically shows up as cams not changing position when asked to by the ecu. mechanison of failure? it's an electro-mechanical part that is probably not rated for as many movements as the salesman told porsche it was.
actuators can fail. this will show up as a sudden increase in deviation at hot idle - in my case it was -16. actuator failure will not cause enough timing change to create valve/piston interference, but you will get a cel and loss of power. actuator failure will also show up as rubbery green bits in the oil sump. mechanism of failure - presume mechanical work due to chain slap. also, failing pads may cause it to extend beyond it's normal range of operation, such that running with bad pads for a long time will eventually result in actuator failure as well.
pads can fail. these will show up as hard dark brown plastic bits in the sump, and a deteriorating deviation over time. there is an updated part for these that lasts longer. again, they fail becuase they get slapped by the chain.
chain slap due to lack of tension on the chains during start-up is a big cause of most of the failures. there are many proposed solutions - updated oil pressure relief piston, tensioners, and pads (porsche improved them for a reason) higher cold weight oil to reduce drain down, pre-oiling via accusump.
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