M272 and M273 Balance Shaft and Timing Chain Repair in Dallas

Which engines and model years are affected?

The window is Mercedes-Benz vehicles with the M272 (3.0 and 3.5 liter V6) and M273 (4.7 and 5.5 liter V8) built from about 2005 to 2008. That spans the W203 and W204 C-Class, W211 E-Class, W221 S-Class, C219 CLS, W164 ML, X164 GL, R171 SLK and R230 SL, among others. Engine serial number, not just model year, decides it.

The settlement that covered this defined the affected engines as M272 serials up to 2729..30 468993 and M273 serials up to 2739..30 088611. Later serials received the updated sprocket. The serial is stamped on the block and recorded in XENTRY, and we read it before quoting.

An engine above the cut-off can still wear a chain and tensioner at high miles, but the catastrophic sprocket wear is largely confined to the earlier build. If yours is near the boundary, the serial read is still worth the hour.

How do you tell balance shaft wear from a stretched chain or a bad cam adjuster?

All three produce correlation codes, so the symptom alone is not enough. XENTRY reports the measured cam-to-crank offset per bank in degrees. Balance shaft wear on the M272 shows up as a large offset on both intake and exhaust of one bank, trending worse over time. A failed cam adjuster usually affects one camshaft and may be accompanied by adjuster-specific codes and a rattle at idle that changes with oil pressure.

We pull the oil filter and look for fine gray metal, which is the sprocket surface coming off. We check the cam adjuster solenoids for the oil wicking problem covered on our oil leak page, since an oil-soaked connector can produce intermittent correlation faults that look mechanical.

If the data points to the balance shaft or idler gear, we say so and quote the job. If it points to a chain and tensioner on a later engine, that is a smaller repair and we quote that instead.

Is the Mercedes settlement coverage still available?

No. The class-action settlement extended coverage to 10 years or 125,000 miles for model year 2005–2007 engines within the serial ranges above, and the claims period closed in 2015. Any car that qualifies today is well outside both limits.

What remains is goodwill. Mercedes-Benz dealers can request a goodwill contribution on a case-by-case basis for a car with a documented service history, and it costs nothing to ask before committing to the repair. Bring your XENTRY report from us; it documents the correlation data and the engine serial.

If goodwill is declined, the repair at independent pricing is the practical route, and the ranges on this page are what Dallas owners should expect from a specialist who does the job with the engine in the car.

What does the repair involve on an M272?

The engine stays in the chassis. The intake manifold, front accessory drive, water pump, timing cover and both camshaft adjuster covers come off. The chain is released, the old balance shaft is withdrawn through the front of the block, and a new shaft with the hardened sprocket and new bearings is installed. Rails, guides and the hydraulic tensioner are replaced as a set.

Both camshaft adjusters are inspected and measured; the chain-side gear teeth wear along with the sprocket, and reusing a worn adjuster is a short road to a second repair. Timing is set with the locking tools, verified by turning the engine through two full revolutions, and then confirmed in XENTRY after the start.

Because the front of the engine is open, the oil cooler seals, thermostat and water pump are a near-zero-labor addition, and we recommend them when the parts are near end of life, which on a 2007 car they usually are.

What is different about the M273 idler gear job?

On the V8 the idler gear sits between the crank sprocket and the two cam chains, and removal requires the timing cover and both cam chain paths to be opened. There is no balance shaft to withdraw, but there are two banks of adjusters, longer chains and more guides, which is why the range for the M273 overlaps the upper end of the V6 job.

The M273 also tends to show the fault on bank 2 first, and owners sometimes arrive after a single-bank adjuster replacement elsewhere failed to clear the code. The idler is the root cause and the adjusters are often fine.

Parts cost is similar between the two engines; the difference is hours. Expect the V8 to be with us at the longer end of the two-to-four-day window, particularly in a W221 or W164 where the front of the engine sits deeper in the bay.

Can you drive the car while you decide?

A car with correlation codes and no rattle can usually be driven short distances to a shop. Once there is a cold-start rattle or metal in the filter, continued driving puts the chain at risk of jumping teeth, which on these interference engines bends valves and turns a four-figure repair into an engine replacement. We would rather you tow it.

A stored code with the light off and the engine running smoothly is a planning window, not an emergency. Use it to get the XENTRY read and the serial number check, and to ask a dealer about goodwill, so that when the rattle does appear the decision is already made.

What does the repair cost in Dallas and what changes the price?

An M272 balance shaft replacement with chain, guides and tensioner runs $4,200–$6,500. An M273 idler gear with chain and guides runs $3,200–$5,000. A chain, guide and tensioner job without a gear, on an engine whose sprocket measures good, is $2,800–$4,800 on either engine.

The variables are whether the cam adjusters need replacement, whether the water pump and oil cooler seals are done at the same time, and the engine's location in the car, since the W164 and X164 give more room than the W203. The work is covered for 2 years parts and 2 years labor, up to 24,000 miles, nationwide, and we will not quote a number until the correlation data and filter inspection are done.