What is the purpose of the cam chain? (1.8t)

[bailor]

Just like the topic says. The timing belt keeps timing, maybe I'm missing something. What is the purpose of the cam chain, chain tensioner and all that hooplah back there? My cam chain tensioner is failing, and I'm getting the chain noise only at certain RPM's. If the tensioner fails what happens? I ask because I have a 650 mile trip I'm supposed to make this weekend and there's no way I can afford to fix this right now. It's made the noise for about a week. Is it something that is dangerous, can it wait for a 2-3 more weeks? Any opinions are appreciated. Thanks.

[diagnosticator]

The timing belt drives the exhaust camshaft, the cam chain drives the intake camshaft from the exhaust camshaft. Drive power flow is: Crankshaft > timing belt > exhaust cam > intake cam drive chain > intake cam.

The intake cam timing adjuster, shifts the slack in the intake cam drive chain from above the center point to below the center point of the timing adjuster travel, the relative position of the slack in the chain advances or retards the intake cam timing with relation to the exhaust cam and crankshaft. The intake cam timing can be adjusted to any value between the advanced and retarded position travel limits of the timing adjuster. The timing adjuster does not tension the chain, the cam chain has a fixed amount of slack and the adjuster only moves the slack in the chain to effect intake cam timing. As long as the adjuster hydraulics are tight, and don't leak, the adjuster is able to dampen the whipping forces in the chain.

[bailor]

The timing belt drives the exhaust camshaft, the cam chain drives the intake camshaft from the exhaust camshaft. Drive power flow is Crankshaft > timing belt > exhaust cam > intake cam drive chain > intake cam.

Well now I feel stupid... You think it's like riding a bike (working on your car), but I've taken some time off and oh how I forget the most simple things.
Just searching around online, I've read about people driving for months with that sound. What is your consensus? Should I park it, or do you think a few weeks would be okay?

[diagnosticator]

See the edited version of my first reply, I believe you will be alright running with the noisy adjuster for awhile. The intake cam induces oscillation forces in the cam chain that cause the chain to whip if there is a lot of wear on the adjuster, because the adjuster can't stabilize the whipping forces in the cam chain, thus the noise. BTW, oil pressure in the head effects the damping capability of the timing adjuster for the chain, as well as wear in the adjuster assembly and chain. Avoid running the engine at speeds that cause the loudest chain noise.

[wmertler]

From what I've read it's usually the pads on it going bad, which costs 20$ compared to 200-300. You can pull the valve cover and look it's on the rear of the head. But like he said oil pressure is key. Have you checked your oil lately, please don't trust the low level sensor.

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[bailor]

See the edited version of my first reply, I believe you will be alright running with the noisy adjuster for awhile. The intake cam induces oscillation forces in the cam chain that cause the chain to whip if there is a lot of wear on the adjuster, because the adjuster can't stabilize the whipping forces in the cam chain, thus the noise. BTW, oil pressure in the head effects the damping capability of the timing adjuster for the chain, as well as wear in the adjuster assembly and chain. Avoid running the engine at speeds that cause the loudest chain noise.

Thanks for your help.. I think I'll chance it and keep my fingers crossed. It only happens between about 1300-1700 rpm. Above those rpm's it's smooth and quiet. When I am coming to a stop or slowing I've been shifting into neutral so the engine just falls below those rpm's and keeps the noise from happening. We'll see what the next few weeks brings. Thanks again.