BenzWorld Junior Member
Date registered: Jul 2006
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I'm presently doing a valve job and timing chain/rail replacements on my '74 450SL, 4.5L engine with D-Jet.
The valves were found to be in excellent condition after 210K miles, with no deterioration of the valve sealing faces nor the valve seats themselves. Minimum wear on the valve stems, but the guides showed signs of bell shape wear and the valve stem seals were found to have lost their resilience, though were not allowing oil past the sealing lips. The cylinders were found to be in excellent condition as well. I am impressed!
Providing your car was well maintained during its life, and gaging by the condition I found my engine to be in -- with nearly twice the mileage as yours -- I don't think an engine rebuild is in order. If anything, replacing the valve stems seals would probably cure the smoking problem. A competent shop, equipped with a leakdown and compression testers could ascertain the condition of the upper end: valves, guides, rings, etc. The bottom end: crank, rods, mains, would probably last 500K before needing attention, and could well go beyond. Again, If the previous owners were religious about compliance with the recommended engine service schedules, there is a good chance your engine is in good condition.
Though it could be done, replacing the valve stem seals is not an easy job to do with the engine in the car, but it can be accomplished without removing the heads or intake manifold. Parts wise, it would not amount to much -- for the valve stem seals, that is. Labor would be costly, but far below that of an engine rebuild. Finding a local, fair-minded, trustworthy mechanic to do the work is imperative. In addition, many times additional parts - hoses, belts, gaskets, filters and such - are replaced as preventative and "on condition" which add to the total outlay for the operation, but may represent savings down the road.