how does the B5 engine retard or advance the timing?

[GLInick]

ive had this question for a while now and hoped to find a good answer but no dice so far. it's about valve timing.

so the timing belt straight run from the crankshaft pulley to the exhaust cam sprocket pretty much determines that the exhaust valves always open and close at the same point during each cycle. given that the intake camshaft is chained to the exhaust timing the only possible way to change the intake timing is by extending or relaxing the cam chain tensioner which runs on oil pressure which is based on engine speed and oil temp.

so does the cct respond to the oil pressure changes to change the timing? i am suspicious that the cct is able to do that. even if it did is oil pressure a good proxy for engine load (which is what i thought determines timing adjustments)?

i am not entirely convinced that the CCT has such amazing capabilities.

if its not the CCT what else could effect when a cylinder starts and stops inhaling?

TIA for any pointers.

[99vwpassataeb]

It depends ..older motors just have the standard cct (no adjustment )..newer ones have a solenoid on the cct that can very slightly advance or retard the timing on the intake cam..exhaust cam doesnt have the option to retard or advance unless you preset it by the timing belt..the only real timing that is ajusted most(by the ecm) is ignition timing..when a cct fails it can/will mess with the intake timing and you should hear top end noise or a cam crank correlation code aka timing over/under advanced or retarded

[zak99B5]

AFAIK, the cct only works to change valve timing at cold start on newer 1.8Ts (B5.5 and later I think) to produce overlap. It then switches back to standard valve timing. It's not like Honda/Toyota VVT that occurs dynamically.

[GLInick]

I have seen somewhere mention of CCTs with solenoids, and mine (ATW) doesn't have one, so I was wondering. I was also very curious why there were so many engine codes, and obviously there must be some differences (aside from basics). So, I tracked down (from the russian website) one document that supposedly compares the various engine characteristics, including valve timing but it seems incorrect on the features of some of the engines, so it's hard to tell how reliable it is.

If on the earlier engines valve timing is fixed, why the CCT, and hydraulic at that? Isn't that overly complicated? Wouldn't some spring loaded gear do just as well? Or is it that even a solenoid-free hydraulic CCT is able to have some effect on intake timing when oil pressure is high (cold-start) and low (engine oil hot).

EDIT: re: throwing a crank correlation code
The cam position sensor sits on the intake cam, so if the CCT cannot vary intake timing, what is the cam sensor's role? All I can think of is so that it can detect anomalies, i.e., the TB skips a tooth, or the cam chain breaks, and post a code and warning message. Is this all the cam sensor is meant to do?

Thanks again for any insight. Don't ask me why, but I find this fascinating (yes, I am an engineer, but not an automotive one).
Nick.

[jollyrogers]

I was trying to figure out how it worked myself. I found a good set of posts on it in the VW forums that may answer some of your questions. It does pretty good at describing what it does.

V.V.T ? - VW Forum :: Volkswagen Forum

[GLInick]

It depends ..older motors just have the standard cct (no adjustment )

AFAIK, the cct only works to change valve timing at cold start on newer 1.8Ts (B5.5 and later I think) to produce overlap. It then switches back to standard valve timing. It's not like Honda/Toyota VVT that occurs dynamically.

Thanks folks. So, on my engine an ATW (circa 2000), why did they put a CCT there if it provides no intake cam phasing, or other adjustment? They could just remove the CCT altogether and have a shorter chain running straight to the camshaft gears.

I guess I don't understand how the CCT operates, or what it does on my engine. Does its tension ever change? Is it just a spring-loaded pair of pads to push the chain taut? Why does it have a mesh screen on the bottom? Does it use oil pressure internally in any way, or is it simply passing oil through to other parts?

V.V.T ? - VW Forum :: Volkswagen Forum

Thanks, that's an awesome thread. It answers some of my questions, but creates new ones too

It's really interesting (among many other things) how they use overlap to re-inhale exhaust gases on a cold engine.

[vbora01]

My best inference for having a CCT is because it accounts for changing engine speed. It keeps the chain tight from 0 all the way to 7200+ RPM. Somehow, I don't believe running just a chain would work at all, the CCT assists in smooth, and quieter operation, with minimal risk of skipping teeth. It has a screen on it to protect it from getting crud in the tensioner itself and ruining the hydraulic surfaces. It uses oil pressure to lubricate surfaces, and to tension the chain. As you rev the motor into higher/extreme RPMs, it accommodates for those changes.