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In many engines, a cooling system failure precedes head gasket repair. Due to thin-walled castings, once a modern motor heats to the point of head gasket failure, the best option is often to replace it entirely with a used one. For owners of the 104 inline six Mercedes engine this is a very real concern. This particular Mercedes engine is an extension of a motor that Mercedes-Benz first introduced in the 1960s. Throughout this engine’s history, it has earned a reputation for being near bulletproof. The 104 is, for the most part, no exception. However, despite its mechanical excellence, it does have an aggravating flaw. It is prone to developing oil leaks. The common point of leakage is where the timing cover’s resilient gasket butts into the head gasket. The resilient seal sits between the upper and the lower case. Had they built this Mercedes engine like most modern motors, with a cam belt, this area would not exist. Yet here it is and this is where the notorious gasket, which is U-shaped, spongy and approximately 4mm thick, resides. In many cases, simply sealing the upper cam housing on the 104 Mercedes engine will cure the problem. If that did not work, then the mechanic replaces the head gasket and reseals the upper cover. However, imagine explaining this to the uninitiated customer. For this reason, many repair shops simply replace the head gasket straight away. This is understandable but also unfortunate since customers could often save substantial money taking that first step. There is a pitfall with this repair on mid-90s versions of this Mercedes engine. Those engines have serious problems with degradation of wire harness insulation. If the harness is in this condition, there is no way to complete the repair without replacing that harness, which is very expensive. Repair shops familiar with this Mercedes engine know to look for it and will often sell you that job as part of the repair. For a late 90s and later 104 Mercedes engine, there are no real pitfalls. The mechanically inclined Mercedes engine owner can accomplish this repair. The first step will be disassembly. First, the mechanic removes the wire harness, and then he removes the head, intake and exhaust in a single unit. Then the process of removing the upper timing cover is simple. At this point, the mechanic should familiarize themselves with the timing marks and orientation. Reseating all of this is paint by numbers except for the cam timer. The cam timer is where you will pay particular attention since a mistake will not always be obvious. This Mercedes engine can run fairly well with the cam timer set incorrectly. In a repair shop, they will hoist the engine, which can be a bit of a challenge even with the proper equipment. It is possible to complete the repair without hoisting the engine. However, some tight fits can prove quite challenging with this Mercedes engine still in place. The most difficult aspect of the job at this point is proper handling of the chain tensioner. The next step, sealing the front cover of the Mercedes engine, which caused the problem to start with, is rather simple. From here, the remaining job is the proverbial piece of cake. About: Take the car for a 5-mile drive. If the Check Engine light comes on, check the vacuum lines to the switchover valve. Getting them backwards is a common mistake with his Mercedes replacement engine. Once it has cleared the short run, take it on an extended test drive and do the scan verification to make sure all codes have cleared.
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