This guide details the reassembly process for the Mercedes OM642 diesel engine, focusing on key components like the oil cooler, intake manifold, and related gaskets and seals. This walkthrough is based on a real-world repair scenario and provides torque specifications directly from the Mercedes repair manual (AlldataDIY), ensuring accuracy and reliability for DIY mechanics and Mercedes-Benz enthusiasts.
Today marks significant progress in the reassembly of the OM642 engine. The arrival of new parts felt like Christmas, particularly the comprehensive seal kit, crucial for preventing future leaks.
Oil Cooler Reinstallation with Updated Seals
With the oil cooler housing now accessible, removing the oil cooler itself was straightforward. It’s secured by 10 T27 Torx bolts. Be prepared for some oil and coolant spillage during removal – ensure thorough cleaning of all mating surfaces before reinstalling the component.
A closer look at the underside of the oil cooler reveals the location of the seals.
The old oil cooler seals, identifiable by their orange color, were noticeably stiff and lacked pliability. This hardening over time and mileage is the primary cause of oil leaks in these engines. The seals exhibited a compressed, set shape, indicating their degradation after years of service.
The replacement oil cooler seals are a distinct purple color and made from Viton rubber, a more durable material designed to address the common leak issue permanently or for an extended period. These purple Viton seals are the updated standard and have been used in Mercedes OM642 Bluetec engines from 2010 onwards. The older orange seals are no longer recommended. If you happen to receive orange seals from a dealership, it’s advisable to return them and request the updated purple Viton versions.
With the new purple seals in place, the oil cooler was reinstalled. The torque specification for the oil cooler T27 Torx bolts is 12 Nm. Ensure all 10 bolts are tightened to this specification.
Intake Manifold Gasket and Reinstallation Challenges
The intake manifold gasket, constructed from aluminum or metal, is quite delicate and can bend easily. It features two hooks, a thoughtful design element to keep the gasket correctly positioned on the intake manifold during installation.
Reinstalling the intake manifold proved to be more challenging than removal. The difficulty stemmed from a coolant joint pipe that needs to be aligned between the intake manifold and the engine block. Compounding this, the surrounding wire harness and fuel lines restricted access and workspace. After approximately 45 minutes of careful maneuvering, the intake manifold finally slipped into place.
The intake manifold tightening sequence is crucial for proper sealing. The torque specification for the intake manifold bolts to the cylinder head is 16 Nm. There are 10 bolts on the left (driver’s side) intake manifold and 9 on the right (passenger’s side), totaling 19 bolts. Follow the tightening sequence illustrated below for optimal gasket compression and sealing.
The coolant joint pipe location is highlighted in yellow in the image below. It is essential to replace this pipe and its seals whenever the intake manifold is removed. A new pipe with fresh seals ensures a leak-free coolant system.
Turbo Oil Feed Pedestal and Gasket Update
Moving to the turbocharger system, the oil feed pedestal was addressed. The old gasket at the base of the pedestal is shown below.
Upon removing the old turbo oil feed pedestal gasket, a seemingly unnecessary hole was revealed in the pedestal base.
After cleaning the pedestal base, it’s ready for the new gasket.
Interestingly, the new turbo oil feed pedestal gasket features an additional hole compared to the old design, and the part number has been updated from A1420280 to A1420681.
Despite the extra hole, the new gasket fits perfectly and does not appear to interfere with the function of the pedestal. This change likely reflects a modular design update by Mercedes-Benz.
With the new gasket in place, the turbo oil feed pedestal is reinstalled. The torque specification for the pedestal bolts is 12 Nm, and there are 4 bolts in total.
Swirl Flap Motor Installation and Clip Replacement
The swirl flap motor is another component requiring attention during reassembly. New clips are essential for securing the motor, as the old ones are prone to breakage due to oil exposure. There are four clips in total: two on the intake manifold and two on the swirl flap motor itself. The new clips are designed to interlock. Installation can be challenging, and it’s recommended to install the swirl flap motor after the intake manifold is mounted to the cylinder head to avoid damaging the fragile clips, swirl flap linkage, and motor mount points.
The old swirl flap clips, saturated in oil, were brittle and on the verge of disintegration, further emphasizing the necessity of replacement.
With new clips, the swirl flap motor is successfully installed. The torque specification for the swirl flap motor bolts is 5 Nm. These bolts should be hand-tightened only. There are two bolts securing the motor.
Fuel Rail Installation and Torque Procedure
Installing the fuel rail assembly presented another challenge. The metal fuel lines protrude approximately 1/4 inch into the fuel rail, requiring careful manipulation to align and seat them correctly, especially the middle lines. Patience and gentle maneuvering are key to successfully seating the fuel lines into the rail. The torque specification for the fuel rail mounting bolts to the valve cover is 9 Nm. There are 2 mounting bolts.
Proper tightening of the fuel rail fuel line nuts is critical to prevent leaks. Follow this procedure:
- Ensure the fuel rail is bolted down.
- Hand-tighten all fuel line nuts. Verify that each nut is threading correctly, not slipping, cross-threading, overlapping, or stripping. This step is crucial.
- Tighten all nuts to 20 Nm.
- Mark a straight line from the rail to each nut.
- Turn each nut an additional 60-degree angle.
- Check for fuel leaks after starting the engine. This procedure applies to all fuel line connections.
The engine reassembly is progressing well and starting to resemble a complete diesel engine once again.
END OF DAY 8
