Mercedes M272/M273 Balance Shaft Failure: How to Check If Your Engine Is Affected

The M272/M273: a great engine with one catastrophic fault

The M272 3.5-litre V6 and M273 5.5-litre V8 petrol engines were used across the Mercedes range from approximately 2004 to 2013 — C-Class, E-Class, S-Class, CLS, SL, ML, GL, and R-Class. They are fundamentally excellent engines: smooth, powerful, and reliable. However, early-production engines (engine serial numbers below 2729..30 468993 for the V6 and 2739..30 088611 for the V8) have a balance shaft sprocket made from a material that wears prematurely. When it fails, the timing chain can jump, causing valve-to-piston contact and catastrophic engine damage. This is not a "maybe" fault — the material defect means the sprocket will wear. The only question is when.

2. How to check if your engine is affected

Every M272 and M273 engine has a serial number stamped on the engine block. The critical threshold for the V6 is engine number 2729..30 468993 — engines below this number are affected. For the V8, the threshold is 2739..30 088611. A Mercedes specialist with Xentry access can read the engine number electronically, or it can be read from the V5C registration document (the engine number is listed). If your engine number is above the threshold, the balance shaft is the revised design and is not affected. If it is below, the engine is at risk.

3. Symptoms of balance shaft wear

Early symptoms include a check-engine light with camshaft/crankshaft correlation codes (P0016, P0017, or Mercedes-specific equivalents) and a rattling noise from the front of the engine that changes with RPM. As wear progresses, the engine may run roughly and eventually fail to start. Do not ignore these symptoms — continued driving will cause valve-to-piston contact, at which point the engine is destroyed.

4. Repair cost and whether it is worth doing

Balance shaft replacement on an M272/M273 is a major job requiring engine removal or partial disassembly. Cost at a specialist: £2,500–£4,000. At a main dealer: £5,000–£7,000. Whether it is worth doing depends on the car's value and condition. An E-Class or S-Class worth £4,000–£8,000 may justify a £3,000 repair. A C-Class worth £2,000–£3,000 typically does not. Many affected cars have already been repaired or scrapped — the youngest affected engines are now 13+ years old — so the number of unrepaired cars still on the road is declining. However, when buying any M272/M273-powered Mercedes, checking the engine number is essential.

Why the balance shaft sprocket wears: the metallurgy problem

The balance shaft on the M272 V6 and M273 V8 engines counteracts the natural vibration of a 90-degree V-engine. It is driven by a sprocket on the timing chain. In early-production engines (engine numbers below the known threshold), the sprocket was manufactured from a material that was not sufficiently wear-resistant for the application. Over time — typically 70,000–120,000 miles — the sprocket teeth wear down, reducing the sprocket's effective diameter. As the sprocket wears, the timing chain can no longer maintain correct tension, and eventually the chain can jump teeth on the sprocket. When this happens, the camshaft timing is lost relative to the crankshaft, causing valve-to-piston contact and catastrophic engine failure. The root cause is a material specification error by Mercedes — not a maintenance issue. Later engines used a revised sprocket material and are not affected.

The cost-benefit analysis: repair or scrap

At £2,500–£4,000 for a balance shaft replacement, the economics depend entirely on the car's value and condition. A 2008 E350 petrol worth £3,000 does not justify a £3,500 repair — the car is effectively a write-off. A 2012 S350 worth £8,000 may justify the repair if the rest of the car is excellent. A 2007 SL350 worth £6,000 sits in the grey area — the repair cost is a large fraction of the car's value, but finding another SL350 in equivalent condition for £6,000 is unlikely. The decision should factor in: the car's overall condition (body, interior, gearbox, suspension), whether any other major items are approaching replacement, and whether you plan to keep the car long-term. A freshly repaired engine in an otherwise good car can deliver another 80,000–100,000 reliable miles — which may be 7–10 years of motoring. That changes the maths significantly.

Checking the engine number before purchase

The engine number is stamped on the engine block and can also be read from the V5C registration document or from Xentry. The critical threshold for the V6 M272 is engine number 2729..30 468993 — engines below this number have the defective sprocket. For the V8 M273, the threshold is 2739..30 088611. If you are viewing an M272 or M273-powered Mercedes, always check the engine number. If the seller will not provide it (or will not allow a Xentry scan), assume the engine is in the affected range and factor £3,000–£4,000 into your budget. A car with the balance shaft already replaced (documented with an invoice, not just a verbal assurance) is worth significantly more than an affected car with no history of replacement.