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Matt, Mechanical Engineer
Category: Audi
Satisfied Customers: 24214
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Im working on a 2001 a4 1.8 . The chain wore a hole in the

Customer Question

Im working on a 2001 a4 1.8 . The chain wore a hole in the rocker cover. I replaced the cct and chain. Also new rocker cover. Its still rattling like mad. What operates the cct and what is the electric solenoid for?
Submitted: 5 years ago.
Category: Audi
Expert:  Matt replied 5 years ago.

the CCT ( cam control unit) is driven off oil pressure thats controlled by the solenoid valve

if you've had a load of swarf / metal around the engine its quite possible that this solenoid is jammed up with debrtis and there could be other oilways also with swarf in them

I'd suggest pulling the solenoid out and replacing it but use some compressed air to blast clear oil ways as best you can

ideally the engine should have been stripped down to clean it properly after this sort of event
Customer: replied 5 years ago.

Would the pick up pipe being clogged cause the cct not to operate? The cct and solenoid have both been replaced. Does the oil pressure determine the operation of the solenoid whick in turn adjusts the chain accordingly?

Expert:  Matt replied 5 years ago.
Hello Angus

you have it right, the actuator uses oil pressure to move so if the pick up was blocked then the unit wouldn't move properly

If the root cause is a blocked pickup that caused the lack of chain tension and then the chain to munch its way through the cover its highly likely that there's other damage so I'd pull the sump off to inspect the oil pickup but also the condition of the mains and big-end shells

if these are damaged then the crank will be too and its at this point you may want to consider sourcing a good used engine as this will be a lot cheaper than building the engine from scratch

Customer: replied 5 years ago.

Cool cool. So the top part of the cct is spring loaded and the bottom run off the solenoid/oil pressure. Does this mean if the solenoid/oil pressure fails the the top guide will compensate by stretching so far the chain is running against the rocker cover?

Expert:  Matt replied 5 years ago.
Hello Angus

the actuators feature an strong internal spring that will return them to a default position and a little dowel springs forth and locks the unit up solid

the unit remains locked up until it sees oil pressure however the chain is tensioned with an oil fed piston so no oil pressure will mean the tensioner will be loose
Customer: replied 5 years ago.

Aha i see. So when the top guide has reached its extent it locks in place. Im a mechy of 9 years but have never come across this setup, thats why its doing my head in trying to understand its operation. So what i fathom if this is.... The oil pressure could be low so the bottom half of the tensioner is not operating. To compensate the loose chain, the top guide has extended to its max and locked in place. The chain still not being tight so flapping off the rocker cover. All this seems to be directing us in the area of the low oil pressure? Does the vvt run off the sensor at the front of the inlet cam or is this also determined by oil pressure?

Expert:  Matt replied 5 years ago.
hello Angus

yes I think the oil pressure is likely to be low, as the VVT unit runs off oil pressure as does the chain tensioner

the sensor at the front of the cam feeds back cam position to the ECU which then moves the solenoid appropiately to drive the cam to the right place

so next job is to measure oil pressure and or have the sump off to inspect the oil pickup