Timing chain adjuster failure on the M157 5.5L twin-turbo V8 is a serious issue that can cause timing chain slack, rough running, and catastrophic engine damage if ignored. This guide covers everything you need to know.
Timing chain adjuster failure on the M157 V8 engine is a known weakness that can lead to timing chain issues, rough running, and potential engine destruction. Early diagnosis is critical to avoid a full engine rebuild.
Full symptom progression, root cause, affected models and cost breakdown below.
Timing chain adjuster failure on the M157 engine rarely happens without warning. The symptoms develop over time, and catching them early can save your engine.
If you notice any of these signs, do not drive the car. Have it inspected immediately. For a broader look at timing chain issues, see our M278 timing chain guide.
The M157 5.5L twin-turbo V8 uses a camshaft adjuster (also called a camshaft phaser) on each cylinder bank to vary valve timing for improved performance and efficiency. The adjuster is hydraulically operated using engine oil pressure. Over time, the internal locking pin or the spool valve can wear, causing the adjuster to fail to lock in position. This results in timing chain slack and erratic camshaft timing. The most common failure point is the internal locking pin, which can become stuck or break, allowing the camshaft to move out of sync with the crankshaft. Oil contamination from neglected oil changes can accelerate wear, as can using the wrong oil viscosity. The M157 engine is particularly susceptible to this issue, especially in higher-mileage vehicles [PATTERN DATA]. If left unaddressed, the timing chain can jump, causing valves to contact pistons.
For more on Mercedes timing chain issues, see our M157 Knowledge Centre.
| Model | Chassis | Engine | Years | Risk Level |
|---|---|---|---|---|
| E‑Class (W212) | 212 | M157 (V8) | 2010–2016 | High – common adjuster failure |
| CLS (C218) | 218 | M157 (V8) | 2011–2016 | High – well documented |
| ML‑Class (W166) | 166 | M157 (V8) | 2011–2015 | High – ageing vehicles |
| S‑Class (W221) | 221 | M157 (V8) | 2009–2013 | Common |
| GLS (X166) | 166 | M157 (V8) | 2012–2019 | Common |
| S‑Class (W222) | 222 | M157 (V8) | 2013–2017 | Common |
| C‑Class (W205) | 205 | M157 (V8) | 2014–2018 | Common |
The M157 V8 engine was used across the high-performance AMG range. If your car has a 5.5L twin-turbo V8 from this era, it's likely an M157. Always verify your engine code. For a complete fitment reference, see our fitment matrix.
The adjuster relies on clean, high‑quality oil. Extended intervals or the wrong oil cause sludge buildup that blocks the hydraulic passages, leading to adjuster failure.
Using oil that's too thick or too thin can prevent the adjuster from functioning correctly. Always use Mercedes‑approved oil with the correct viscosity.
Adjusters typically fail after 60,000–100,000 miles on the M157. The high-performance nature of the engine accelerates wear.
Frequent high‑revving and aggressive driving put extra stress on the timing system, accelerating adjuster wear.
Using Mercedes STAR diagnostic tool, the specialist reads fault codes related to camshaft timing (P0011, P0012, P0021, P0022). These indicate incorrect camshaft position.
Low oil pressure can prevent the adjuster from working correctly. The specialist checks oil pressure to rule out pump or oil level issues.
The timing chain and adjuster are inspected by removing the valve cover. A worn adjuster may have visible play or broken internal components.
Using diagnostic software, the specialist monitors camshaft position data while the engine is running. Deviations from expected values confirm adjuster failure.
If you're not sure what's wrong, try our Diagnostic Wizard to narrow it down.
The cost of fixing timing chain adjuster failure varies depending on how early it's caught. Early intervention is far cheaper than engine replacement.
| Stage | Supply & Fit (Indie) | Main Dealer Est. |
|---|---|---|
| Diagnostic Labour (1–2 hrs) | £80–£150 [INDUSTRY ESTIMATE] | £200–£300 |
| Camshaft Adjuster Replacement (one bank) | £1,500–£2,500 | £3,000–£4,500 |
| Both Adjusters + Timing Chain + Guides | £2,500–£4,500 | £5,000–£7,500 |
| Engine Rebuild / Replacement | £7,000–£12,000 | £12,000–£18,000 |
Labour times: adjuster replacement 8–12 hours, with chain and guides 12–16 hours. Prices are indicative for 2025; always obtain a written quote for your specific vehicle.
You can reduce the risk of timing chain adjuster failure and catch issues early.
For a broader view of engine longevity, see our Repair vs Replace vs Scrap Framework.
⚠️ Watch – but almost always worth fixing on AMG models.
Our data flags timing chain adjuster repair as Watch only for the worst‑case scenarios on very low‑value vehicles [PATTERN DATA]. On most M157‑equipped AMG models with a realistic value of £10,000+, the repair is well within the car's worth – typically under 35% of the value. If caught early, a single adjuster replacement is usually cost‑effective. Always get a current valuation and a firm quote. See the full economics framework for a worked example.
If you're still uncertain, compare this issue to the M157 black smoke guide or read real owner decisions in our case studies section.
The earliest signs are a brief rattling noise on cold start, a rough idle, and a check engine light with camshaft position codes.
No. If the adjuster fails completely, the timing chain can jump, causing valves to hit pistons. This leads to catastrophic engine damage. Stop driving and have it inspected immediately.
At an independent specialist, expect £1,500–£2,500 for one adjuster, and £2,500–£4,500 if both adjusters and the timing chain need replacement. Main dealer prices are significantly higher.
It depends on the vehicle's value. On an AMG worth over £10,000, the repair is usually worthwhile. On a sub‑£8,000 car, evaluate whether the car is otherwise in good condition.
Regular oil changes with the correct oil are the best prevention. Using Mercedes‑approved oil and changing it every 10,000 miles significantly reduces the risk.
The M157 is the 5.5L twin-turbo V8 used in AMG models from 2010–2017. The M278 is the 4.7L twin-turbo V8 used in non-AMG models. Both can have timing chain issues, but the failure modes differ.
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