If you’re a Mercedes-Benz Sl550 owner or are considering purchasing one, understanding potential engine issues is crucial. Specifically, some models, particularly those with the M273 V8 engine produced around 2006 and 2007, may be susceptible to premature timing chain sprocket wear. This article delves into this issue, providing you with essential information to assess and address any concerns related to your SL550.
The issue stems from a manufacturing defect in the heat treatment process of the timing chain sprocket. This sprocket, acting as an idler for the timing chain, was intended to be robust. However, due to incorrect heat treatment, some sprockets were made with softer metal, leading to accelerated wear. In the SL550, equipped with the M273 engine (which doesn’t have a balance shaft unlike the V6 M272), this idler sprocket is bolted to the front of the engine block and plays a crucial role in guiding the timing chain between the camshaft banks.
When this sprocket wears down, it introduces slack in the timing chain. Because the crankshaft pulls the chain down from the right-bank camshaft, the timing remains correct on that side. However, as the chain travels around the worn sprocket, the distance between the sprocket and the right camshaft effectively shortens. This causes the right camshaft position to become retarded, or lag behind the crankshaft’s timing.
This timing chain slack primarily accumulates between the crankshaft and the right camshaft. In some cases, this slack can manifest as an audible chain rattle, especially noticeable upon engine startup. Accompanying this, diagnostic trouble codes, specifically 1200 and 1208, might be triggered. Initially, these error codes might appear intermittently, but as the sprocket wear worsens, they can become persistent, appearing as “CURRENT” errors immediately after starting the engine.
Fortunately, the variable valve timing system in the M273 engine can compensate for minor discrepancies in the right bank’s camshaft angle. This means that significant engine damage is not an immediate threat. However, prolonged wear can eventually lead to more serious problems. The timing chain itself could become damaged due to slapping or scraping against a severely worn sprocket. In rare scenarios, fragments from the disintegrating sprocket could migrate to other internal engine components, causing further complications.
This potential manufacturing issue primarily affects Mercedes-Benz vehicles with M272 V6 and M273 V8 engines produced up to mid-2007. For SL550 models, this generally includes those from the 2007 model year and potentially some very early 2008 models, as the manufacturing revision occurred roughly halfway through the 2007 model year production.
To determine if your SL550 falls within the potentially affected range, you need to check the engine serial number. You can obtain this number from the vehicle’s data card or build sheet, accessible using the VIN (Vehicle Identification Number). Online VIN decoder websites, such as VIN Decoder for Mercedes-Benz, can provide this information.
For M273 V8 engines, if the serial number is 30 088611 or earlier, it is within the range of potential premature failure. Engines with serial numbers after this threshold are considered to be outside the affected range.
It’s important to understand that “potential premature failure” doesn’t guarantee failure, but indicates an increased risk. While some engines within the affected range have experienced issues at low mileages (under 30,000 miles), others have shown no symptoms well beyond 100,000 miles. The exact lifespan of the component is uncertain, but failures under 250,000 miles are generally considered premature.
Therefore, if you are considering purchasing a used Mercedes-Benz SL550 from the affected years, especially a 2007 model, it is advisable to verify if the timing chain sprocket issue has already been addressed. Alternatively, factor in the potential cost of repair if purchasing a vehicle within the serial number range. Even as a do-it-yourself project, parts for the V8 engine can be costly.
While the original author’s 2007 SL550, fortunately, was manufactured after the affected serial number range and ran flawlessly up to 98,000 miles, understanding this potential issue is vital for any SL550 owner or prospective buyer. By checking the engine serial number, you can proactively assess the risk and ensure the longevity and performance of your Mercedes-Benz SL550.
