Replacing the timing chain guides on your Mercedes Benz Sec can seem daunting, but with the right knowledge and mechanical aptitude, it’s a task that can be undertaken by experienced DIY enthusiasts. However, it’s crucial to understand that this is not a job for beginners. Improper execution can lead to significant engine damage and costly repairs. This guide, intended for those with a solid background in automotive mechanics, outlines the process, emphasizing key steps and precautions.
It’s important to recognize the symptoms of worn timing chain guides in your Mercedes Benz SEC. Often, the first sign is a rattling noise from the engine, particularly noticeable on startup or idle. This noise can be intermittent at first, but will become more persistent as the guides wear further. Ignoring these warning signs can lead to serious engine damage, including bent valves and even complete engine failure.
One of the most common failure points is the passenger side inboard guide, as depicted below. These guides are designed to be stationary, providing a smooth surface for the timing chain to run against. Over time, the plastic or nylon material of these guides can become brittle and fracture due to heat, age, and constant chain pressure.
A fractured timing chain guide, a common issue in older Mercedes Benz engines, highlighting the wear and potential for failure.
The image above illustrates a fractured guide. In many cases, the fractured piece can fall into the path of the timing chain, creating a dangerous situation. As highlighted in the accompanying video (originally provided), a fractured guide can cause the timing chain to jump or skip teeth on the sprockets. If the top portion of a fractured guide falls into the chain path, it can lead to valve timing interference, where the valves collide with the pistons. This often results in bent valves, necessitating cylinder head removal and extensive repairs.
While this guide focuses on the upper timing chain guides (cylinder head guides and tensioner guide), it’s worth noting that there are also lower guides located behind the timing cover, along with an oil pump chain tensioner guide. Accessing these lower guides is significantly more labor-intensive, often requiring engine removal or at least cylinder head removal for easier timing cover reinstallation. Due to the extensive labor, these lower guides are often addressed during a full engine overhaul. Fortunately, the upper guides are generally more prone to failure than the lower ones. However, for a truly comprehensive approach, replacing all guides is ideal, albeit a much larger undertaking.
For many DIY mechanics, replacing the three upper cylinder head guides, the tensioner guide, the tensioner itself, and the timing chain is a practical compromise. For this critical job, using only Original Equipment (OE) Mercedes-Benz parts or parts specifically approved by reputable Mercedes-Benz parts suppliers is strongly recommended. Aftermarket parts may not meet the stringent quality and durability standards required for these vital engine components.
The procedure described here is based on a 1989 Mercedes Benz 560 SL, and the general principles apply to other Mercedes Benz 560 models, although minor variations in engine attachments may exist. While the original procedure was demonstrated with the intake manifold removed, it’s important to note that intake manifold removal is generally not necessary for timing chain guide replacement and was done in the original context for separate seal-related maintenance.
This guide assumes you have already removed components for access, specifically the valve covers, power steering pump and bracket, and alternator and bracket. In many cases, the power steering pump and alternator can be carefully moved aside without fully disconnecting them.
Driver’s side camshaft timing marks aligned, a crucial step in ensuring correct engine timing during timing chain guide replacement on a Mercedes Benz SEC.
The first crucial step is to align the engine timing marks. As shown in the photo above, locate the timing marks on the driver’s side camshaft. Ensure these marks are precisely aligned as per your Mercedes Benz SEC service manual.
Passenger’s side camshaft timing marks properly aligned, mirroring the driver’s side to confirm accurate engine timing for the Mercedes Benz SEC repair.
Next, verify the timing marks on the passenger’s side camshaft are also correctly aligned, as shown in the picture above. Accurate alignment on both camshafts is essential for maintaining proper engine timing.
Engine set at TDC, with tie-wraps used to secure the timing chain to the sprockets, a helpful technique for DIY Mercedes Benz SEC timing chain guide replacement.
Set the engine to Top Dead Center (TDC) on cylinder number one. Using tie-wraps, as illustrated above, can be a helpful technique to secure the timing chain to the camshaft sprockets. This prevents the chain from slipping or losing its position during sprocket removal. This is particularly useful when working alone. When loosening the camshaft sprocket bolts, using an impact wrench can be beneficial for quickly breaking them free. However, exercise caution to avoid damaging the camshaft or surrounding components.
Driver’s side camshaft marked and secured, preparing for camshaft sprocket bolt removal during the Mercedes Benz SEC timing chain guide replacement process.
Before removing the camshaft sprocket bolts, mark and secure the camshaft, as shown above for the driver’s side. This ensures the camshaft doesn’t rotate unexpectedly when the sprocket is removed, which could disrupt the engine timing.
Crankshaft timing marks aligned at the zero position, confirming TDC and correct base timing for the Mercedes Benz SEC engine repair.
Verify that the crankshaft timing mark is pointing to the zero position, confirming TDC. Additionally, check that the ignition distributor rotor is pointing to the #1 cylinder position. These checks, along with the aligned camshaft marks, confirm that the engine is correctly positioned for timing chain guide replacement.
Using an impact wrench to carefully loosen the camshaft sprocket bolt, a step in removing the sprocket for timing chain guide access on a Mercedes Benz SEC.
Using an impact wrench, apply a brief burst to loosen the camshaft sprocket bolt. It’s highly advisable to secure the camshaft with channel-lock pliers or a specialized camshaft holding tool. There are nubs on the camshaft designed for this purpose. However, be extremely careful around the camshaft oiling tube and its plastic clips, as they are fragile and easily broken. Once the bolt is loosened, it should be removable by hand.
After removing the bolt, prepare a wire to suspend the timing chain from the hood or another secure point. Ensure there is enough slack in the wire to allow movement while working with the sprocket. Use the wooden end of a hammer to gently tap the backside of the sprocket to loosen it. Avoid using the steel end of a hammer, and while a rubber mallet might seem suitable, small rubber pieces can sometimes break off and fall into the engine, which is undesirable. A few firm taps with the wooden hammer end should start to move the sprocket. Wiggle and pull the sprocket towards you, being mindful of the timing chain.
Removing the camshaft sprocket while carefully supporting the timing chain, preventing it from falling into the engine during Mercedes Benz SEC timing chain guide work.
When the camshaft sprocket comes off, immediately hold the timing chain up to prevent it from falling into the engine case. It’s crucial that the chain remains taut. Use the pre-positioned wire to suspend and secure the chain while you proceed with guide replacement.
A washer exposed after camshaft sprocket removal, a small but critical component to prevent from dropping into the engine during Mercedes Benz SEC timing chain guide replacement.
Be mindful of the washer behind the sprocket. It can easily fall into the engine if you’re not careful. To prevent loss, temporarily reinstall the camshaft sprocket bolt, hand-tight, to retain the washer.
Camshaft sprocket bolt hand-tightened to secure the washer, a preventative measure against losing this small but important part during the Mercedes Benz SEC repair.
The bolt, hand-tightened, now secures the sprocket washer and timing mark components to the camshaft, preventing them from falling into the engine.
Using a homemade puller tool to extract timing chain guide pins, a method for removing the worn guides in a Mercedes Benz SEC engine.
Removing the guide pins can be straightforward with experience. Specialized tools are available for pulling these pins, but a DIY approach, as shown above, using valve cover bolts, a socket, and washers can be effective. When using a DIY puller, or even a professional tool, extreme care is necessary to avoid jamming the pin during extraction. Uneven surfaces around the pin can cause binding, requiring shims or spacers to create a level pulling surface. Stripping the threads of the pin is a risk if it binds during removal. If the threads are stripped, a high-quality steel screw and pry bar might be necessary to remove the pin, and a replacement pin will be required.
A timing chain guide pin partially extracted, showing progress in removing the pin to release the old guide in a Mercedes Benz SEC engine.
As shown above, once the pin is partially pulled, it should be possible to remove it completely by hand.
The last timing chain guide pin being removed, requiring the guide to be held to prevent it from falling into the engine once the pin is fully extracted in a Mercedes Benz SEC.
The pin in this photo is the final pin securing the guide. Ensure you are holding the guide firmly to prevent it from falling into the engine once this last pin is removed.
A side-by-side comparison of an old, worn timing chain guide and a new Mercedes-Benz guide, illustrating the wear and degradation of the old part.
This photo shows a direct comparison between an old, worn guide and a new OE Mercedes-Benz guide. The difference in material condition is often noticeable; old guides become brittle with age.
Installing the new timing chain guide and pushing the pins through, ensuring proper alignment with the cylinder head in a Mercedes Benz SEC engine.
Slide the new guide into position and push the pins through, aligning the holes in the guide with those in the cylinder head. You may need to lightly tap the pins to overcome the initial resistance of the plastic, but use minimal force. Ensure the pins are slightly started in their bores before fully driving them in.
Sealant being applied to the ends of the timing chain guide pins to prevent oil seepage, a final step in securing the new guides in a Mercedes Benz SEC engine.
Apply sealant to the ends of the pins to prevent oil seepage. This is a crucial step to ensure a leak-free seal after guide replacement.
After installing the new guides and tensioner, and verifying correct timing, reassemble the removed components in reverse order. Always consult your Mercedes Benz SEC service manual for specific torque specifications and procedures. While this guide provides a detailed overview, professional expertise and the correct tools are essential for a successful timing chain guide replacement on your Mercedes Benz SEC.
