Mercedes-Benz Timing

A gear that wore out
because of how it was made.

On a specific range of Mercedes V6 and V8 engines, a sprocket in the timing drive was manufactured softer than it needed to be. The teeth wear, the timing drifts, and the car tells you with a code long before it tells you with a noise.

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The Symptom

A code first,
usually.

Unlike most timing problems, this one is frequently found by the diagnostic system before the driver notices anything at all.

"Check engine light, and it says camshaft"
Camshaft position correlation codes — the engine reporting that the camshafts are not where the crankshaft says they should be. This is the classic first sign, and on the affected engines it is the reason most cars arrive.
"It rattles briefly on a cold start"
A short metallic chatter from the front of the engine on start-up. Where the wear has progressed to the point of producing audible slack, it is further along than the code-only stage.
"It runs rough, or it is down on power"
Timing outside specification costs smoothness, power and economy, and the engine management compensates until it can no longer do so cleanly.
"It has been to a shop and they replaced sensors"
Camshaft correlation codes name the sensors, so the sensors are frequently replaced first. On these engines the sensors are usually reporting accurately — the timing genuinely has drifted, and the sensor was the messenger.

Why It Happens

A known defect,
in a known range.

This is not general wear and tear. It is a specific manufacturing issue affecting particular engines built in a particular period, which is unusually good news diagnostically because it means the answer is partly determinable from records rather than only from disassembly.

The V6 Balance Shaft Gear
On the affected V6 engines, the balance shaft gear was produced from material that did not hold up. Its teeth wear progressively, the balance shaft falls out of its correct relationship with the rest of the timing drive, and the engine management sees and reports the deviation.
The V8 Idler Gear
The V8 of the same era has the equivalent problem in a different component — an idler gear in the timing drive, wearing for the same underlying reason and producing the same class of correlation fault.
The Engine Number Tells You
Because the issue is confined to a production range, the engine serial number is genuinely diagnostic. Establishing whether your specific engine falls inside the affected range is one of the first things we do, and it is a step that a shop without model-specific information will not know to take. It changes both the likelihood and the recommended approach.
Why It Is Not A Small Job
These components sit at the back of the engine, and access is the overwhelming majority of the cost. We would rather be direct about that early than have you discover it partway through. If your car is in the affected range and showing correlation codes, the sensible thing is a firm diagnosis and a clear number before any work begins.

What We Do

Confirm it is the gear
before opening anything.

Correlation codes have several possible causes, and only some of them justify a job of this size. The difference matters a great deal here.

How Level 1 Testing Confirms It
With XENTRY we read complete fault memory including stored and intermittent correlation faults, and we examine live camshaft deviation values against specification with the engine warm and running. We check the engine serial number against the affected range. We evaluate the other plausible causes — a stretched chain, oil condition and level affecting the chain tensioner, or a genuinely failed sensor — so that a major repair is recommended only when the evidence supports it. That is a Level 1 Testing session at $285 flat.
The Repair
The worn gear is replaced with the updated part, along with the chain and guides where they show wear, because reusing a worn chain against a new gear wastes the labour that dominated the cost. Timing is set and verified to factory specification, and we confirm with live deviation data afterwards that the engine agrees with what we did. We will give you the full figure before we start, not after.
Why OEM Matters On This Job
The entire point of the repair is that the replacement part is made of better material than the original. That is precisely the property an aftermarket copy is least likely to reproduce, and on a repair where labour so heavily outweighs parts, fitting an unknown-quality gear is the worst possible economy. OEM or genuine manufacturer-specification components, with a 3-year/36,000-mile warranty.

Related

Other jobs
on these cars.

Every job we have written up is listed on Common Repairs. For everything this platform needs, see the Mercedes-Benz page.

Mercedes-Benz AIRMATIC Air Suspension Repair Audi Timing Chain and Tensioner Repair BMW N63 V8 Service and Repair All Mercedes-Benz service → All common repairs →

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