Replacing the timing chain guides in your Mercedes-Benz SEC can be a necessary but complex maintenance task. This guide is designed for individuals with a solid understanding of automotive mechanics. If you’re not experienced in car repairs, it’s crucial to understand that this job carries risks and could lead to significant expenses if not performed correctly. This article provides a step-by-step overview based on a real-world repair scenario, focusing on the upper timing chain guides, which are commonly prone to failure.
One of the most common issues is a fractured timing chain guide. Below is an example of what a damaged guide can look like. This particular guide, located on the passenger side, was broken in the center, demonstrating a critical failure point. These guides are designed to be stationary, so any fracture indicates a serious problem.
As shown in the image above, a fractured guide can quickly lead to further complications. In many cases, the broken piece can fall into the path of the timing chain and sprockets. If the top portion of the guide obstructs the chain, it can cause valve interference, potentially bending the valves and leading to costly engine damage. It’s vital to address worn or broken timing chain guides promptly to prevent such severe issues.
Beyond the three cylinder head guides and the tensioner guide, there are also two lower nylon guides located behind the timing cover, along with another tensioner guide for the oil pump chain. Accessing these lower guides is significantly more labor-intensive, often requiring engine removal. Therefore, replacement of the lower guides is frequently deferred until a complete engine overhaul. While these lower guides are generally less problematic than the upper ones, they are still subject to wear and tear. Replacing them while the engine is out, or at least removing the cylinder heads, simplifies the process of reinstalling the timing cover.
Consequently, many DIY mechanics opt to replace only the upper cylinder head guides, the tensioner guide, the tensioner itself, and the timing chain. For this type of repair, using Original Equipment (OE) Mercedes-Benz parts, or parts specifically approved by reputable Mercedes-Benz parts suppliers, is strongly recommended to ensure compatibility and longevity.
The following steps are based on a repair performed on a 1989 Mercedes-Benz 560 SL. The procedure is generally similar for other 560 models, with minor variations depending on engine attachments. Although the intake manifold was removed in the original repair for unrelated maintenance, it’s not necessary to remove it for timing chain guide replacement.
The subsequent photos illustrate the process, starting after the valve covers, power steering pump and bracket, and alternator and bracket have been removed. Often, the power steering pump and alternator can be moved aside without complete disconnection.
In the image above, you can see the timing marks being aligned and marked on the driver’s side. The small marks in the center of the camshaft are aligned to ensure correct timing.
This photo demonstrates the timing marks alignment on the passenger’s side camshaft, mirroring the driver’s side for precise synchronization.
Here, the engine is set to Top Dead Center (TDC). Using tie-wraps to secure the chain and sprocket can be helpful, especially when working alone. This prevents the chain from slipping and aids in using an impact wrench to loosen the camshaft bolt. Exercise caution to prevent components from falling into the engine.
This image shows the driver’s side camshaft marked and secured before removing the camshaft sprocket bolt. This step is crucial to maintain timing integrity.
This photo illustrates the crankshaft timing marks pointing to the Zero position, indicating TDC. Additionally, ensure the ignition distributor rotor points to the #1 cylinder position to confirm correct engine timing.
Using an impact wrench, apply a quick burst to loosen the camshaft bolt. Secure the camshaft with channel locks, utilizing the nubs in the center of the cam, while carefully avoiding damage to the camshaft oiling tube and its plastic clips. Once loosened, the bolt should unscrew by hand.
As the cam sprocket is removed, support the timing chain to prevent it from falling into the engine. Use a wire to suspend the chain, keeping it taut while you replace the guides.
Be mindful of this washer, as it can easily fall into the engine. Reinstall the bolt temporarily to secure the sprocket and prevent the washer from dropping.
Here, the bolt is hand-tightened to keep the sprocket and washer in place on the camshaft, ensuring no parts are lost during the guide replacement.
Removing the guide pins can be challenging. Specialized tools are available, but a DIY puller can be fashioned using valve cover bolts, a socket, and washers. Exercise caution to avoid stripping or bending the pins during removal. Uneven surfaces may require shimming to ensure a straight pull.
This image shows a guide pin partially extracted. Once pulled out to this extent, the pin should be removable by hand.
This is the final pin securing the guide. Hold the guide firmly to prevent it from falling into the engine once this pin is removed.
A comparison of the old, brittle guide with a new Mercedes-Benz replacement highlights the degradation of these plastic components over time and heat cycles.
Slide the new guide into position and push the pins through. Align the guide holes with those in the cylinder head. Light tapping may be necessary to overcome initial resistance.
Apply sealant to the pin ends to prevent oil seepage. This crucial step ensures a leak-free seal after the new guides are installed.
Replacing the timing chain guides on your Mercedes-Benz SEC is a detailed procedure that demands patience and mechanical competence. Using high-quality, preferably OE Mercedes-Benz parts, is crucial for a reliable and lasting repair. While this guide provides a comprehensive overview, always consult your vehicle’s service manual and consider seeking professional assistance if you are uncertain at any step. Proper maintenance, including timely replacement of timing chain guides, is essential for preserving the performance and longevity of your Mercedes-Benz SEC engine.
