For owners and enthusiasts of the Sl550 Mercedes-benz, understanding the intricacies of its engine is paramount. Like many sophisticated vehicles, certain model years of the SL550 can be susceptible to specific mechanical issues. One such concern that has surfaced involves the balance shaft and timing chain components in particular engines. This article will delve into this issue, providing clarity and guidance for SL550 owners and prospective buyers.
Decoding the Balance Shaft and Timing Chain Sprocket Problem
The issue at hand primarily affects Mercedes-Benz vehicles equipped with the M272 V6 and M273 V8 engines produced up to around mid-2007. In these engines, a critical component known as the balance shaft (in V6 engines) or a simple idler sprocket (in V8 engines) for the timing chain can experience premature wear.
This wear stems from a manufacturing defect related to the heat treatment process of the sprocket. Incorrect heat treatment resulted in a softer metal, causing the sprocket to wear down more rapidly than intended. As this sprocket deteriorates, it introduces slack into the timing chain.
In the V6 engine, the sprocket is an integral part of the balance shaft. The V8 engine, lacking a balance shaft, utilizes a separate idler sprocket. Regardless of the engine configuration, this sprocket plays a crucial role in guiding the timing chain, specifically creating the “V” shape between the engine’s cam banks.
The crankshaft, responsible for pulling the timing chain downwards from the right-bank cam, maintains proper timing on that side. However, as the chain navigates around the worn sprocket, the distance between the sprocket and the right camshaft effectively shortens. This discrepancy leads to the camshaft position becoming “retarded,” or lagging behind the crankshaft’s timing.
This timing chain slack primarily accumulates between the crankshaft and the right camshaft. One of the initial symptoms can be an audible “chain rattle,” accompanied by diagnostic trouble codes (DTCs) 1200 and 1208. Initially, these error codes might appear intermittently. However, as the sprocket wear progresses, these codes will become persistent, registering as “CURRENT” immediately upon engine startup.
Fortunately, the variable valve timing system present in these engines can partially compensate for the timing discrepancy on the right bank. This means significant engine damage is not an immediate threat. However, prolonged neglect can lead to more serious issues, such as a damaged timing chain due to excessive slapping or scraping against the severely worn sprocket. In rarer instances, fragments from the disintegrating sprocket could potentially migrate to other internal engine areas, causing further complications.
Identifying Affected SL550 and Other Mercedes-Benz Models
These M272 and M273 engines were deployed across a wide range of Mercedes-Benz models. Starting with the SLK350 in model year 2005, these engines became widespread by model year 2006 and continued to be used in all non-AMG V6 and V8 Mercedes-Benz vehicles until approximately model year 2011. The manufacturing correction addressing the sprocket issue was implemented around late 2006, roughly midway through the 2007 model year production cycle.
Consequently, all model year 2006 (along with the 2005 SLK350) non-AMG V6 and V8 Mercedes-Benz models fall within the range of potential balance shaft/idler sprocket failure. Furthermore, approximately half of the vehicles sold as model year 2007 may also be affected.
To definitively determine if a specific 2007 model year SL550 Mercedes-Benz, or another model with these engines, is within the affected range, you need to check its engine serial number. This crucial piece of information can be accessed via the vehicle’s data card, also known as the build sheet, obtainable using the Vehicle Identification Number (VIN). A helpful online resource for this purpose is the VIN Decoder for Mercedes-Benz.
Crucially, if the V6 engine serial number is 30 468993 or lower, or if the V8 engine serial number is 30 088611 or lower, the engine is within the potential premature failure range. If your engine serial number falls after these thresholds, it indicates that your vehicle is equipped with the updated, corrected part.
It’s important to understand the term “premature failure.” These sprockets are mechanical components subject to wear over time. While a definitive lifespan is not publicly specified, failures occurring before 250,000 miles could be considered premature. Due to the proprietary nature of this information, the exact failure rate within the affected engine range remains unknown outside of Mercedes-Benz and their suppliers. It’s understood that engines within the range could experience this failure, but not all will. Some failures have occurred very early, even before 30,000 miles, while others have manifested symptoms well beyond 100,000 miles.
Therefore, the prudent approach is to exercise caution when considering purchasing a used SL550 Mercedes-Benz or any other affected model with an engine serial number within the at-risk range. Unless you can verify that the repair has already been performed, or negotiate a purchase price that adequately accounts for the potential repair cost, it’s wise to be wary. Even as a do-it-yourself (DIY) project, replacing these components can be costly. For V6 engines, parts alone can exceed $1,000. While the V8 engine parts are somewhat less expensive, and technically the engine doesn’t require full removal (just lifting) for oil pan clearance, the labor and complexity remain significant.
My personal experience reflects this situation. My 2007 SL550, with 98,000 miles when traded, ran flawlessly. Fortunately, its production date was after the implementation of the corrected parts. Similarly, my 2008 S550 with the M273 engine and 140,000 miles, and a 2008 GL450 with 137,000 miles (traded for a 2013 GL450), also performed like new. These experiences highlight that not all engines within the identified ranges will necessarily fail, but the potential risk exists, especially in earlier production years.
Conclusion: Informed Decisions for SL550 Owners and Buyers
Understanding the potential balance shaft and timing chain sprocket issue in certain SL550 Mercedes-Benz models and other vehicles with M272 and M273 engines is crucial for both current owners and those considering a purchase. By verifying the engine serial number and being aware of the symptoms, owners can proactively address any potential problems. Prospective buyers can make informed decisions, mitigating the risk of unexpected and costly repairs. While this issue is a known concern, it’s important to remember that Mercedes-Benz vehicles, including the SL550, are generally renowned for their engineering and longevity. Taking the necessary precautions ensures a continued enjoyable ownership experience.
