Above: Because my goal is to put the car back to factory-fresh condition and this isn’t my first rodeo, I decided to do the complete top-to-bottom rebuild myself.


Restoration Project
By Andrew Atwood

Doing the Powertrain
Part Seven of an ongoing series
 
With the chassis and body panels at the body shop and the suspension on my workbench, I had to get started with the heart of the car, the engine and transmission.Throughout my years as a technician, I have seen some engines amazingly restored by amateur mechanics and some pretty sad hack jobs from so-called certified Mercedes experts. Like other aspects of the restoration, the decision to do the work yourself or farm it out – and how deep to go – starts with what type of restoration you are doing and the confidence you have in your abilities. In this case, I’m doing a full restoration to put the car back to day-one condition and this isn’t my first engine: I decided to do the complete top-to-bottom rebuild myself. However, if you’re just doing a clean-up restoration on a running car or you don’t have the space, time or basic mechanical skills, your strategy would be different.

Now you’ll need to establish the engine’s condition to determine how deep you will have to go. I start with compression and cylinder-leakage tests, which can tell you a great deal about an engine without even starting it. The familiar compression test will reveal the condition of rings, pistons, timing, valves and camshafts. The less familiar cylinder-leakage test will indicate where any deficiencies may exist.

These tests can save lots of time and even more money. For example, a customer brought me his 1969 280SE for an engine rebuild because the car was running rough and he had already changed plugs, wires, cap, rotor and even the mechanical injectors. Before tearing into it blindly, I wanted to establish exactly what was causing the engine to run rough.

The compression test established that there was a significant loss of compression in one cylinder. My next step was to determine where compression was being lost. By using a pressure differential gauge and some compressed air, I heard air escaping through the intake manifold, as well as the exhaust pipe. This was good news – the worst we were looking at was a valve job or perhaps just a simple valve adjustment.

Sure enough, I found that every valve was not adjusted properly. After correcting the adjustments on all the valves, I got good compression in all cylinders and the cylinder-leakage at a respectable 15 percent loss or less per cylinder. Now we had an engine worth keeping. I changed the oils, set the timing and dwell, and it fired right up and idled smoothly. The customer was ecstatic that a valve adjustment and tune-up fixed what he thought was a dead engine. The moral of this short story is don't jump to conclusions too quickly; they can get costly.

Now let’s assume the worst: engine valves that have the same compression readings, or even worse, an engine that won’t turn over or has a loud knock indicating bottom-end damage. While this is everyone’s worst nightmare, it’s not the end of the world. The same test procedures can minimize the amount of work needed.

If the compression test is good, then it’s the bottom-end knock that needs to be repaired. In this case, the oil pan and crankshaft can be removed, repaired and reinstalled. Again, this is a viable option as long as all the proper tests were performed to identify the problem. Moral: The more thorough the inspection and diagnosis, the cheaper the repair can be.

If the engine is in poor shape and does require a complete rebuild, this task needs to be planned and budgeted – An average 1960s Mercedes 6-cylinder rebuild done at a professional shop can run in excess of $7,000 and a V-8 can go as high as $9,000 for parts and labor. Cost is the biggest deciding factor with most engine builds, but corners cut will always come back to haunt you.

Because I wanted my engine to really stand out, my plan was to build one that would look better than new and would run so well it would make a Mercedes engineer proud. I found a donor engine in a 1991 560SEL that had been hit hard in the rear; the engine was about the only thing worth salvaging. I would keep the engine completely stock for reliability reasons but use a complete Euro-spec 500 fuel system for simplified fueling, lower maintenance needs and improved reliability.

I had already checked out this engine when it came into the shop, so I removed it from the donor car without doing any further diagnosis. I didn’t to take any pictures of the teardown since I’m familiar with M116 and M117 engines, but I don’t recommend this approach to someone rebuilding an engine for the first time. Photographs, meticulous notes, a solid and organized plan, as well as careful attention to the workshop manual are critical because it’s very easy to bend valves or create more damage to the engine if the disassembly is careless.

With the engine dismantled, I delivered the cylinder heads, lower rotating engine components and engine block to my local machine shop, which is experienced with Mercedes engines.

Finding a machine shop that knows the intricacies of the all-aluminum Mercedes-Benz engines is critical because of the technology used. For example, Mercedes began using Alusil hypereutectic alloy engine blocks in the 380 V-8 in 1980. The engine blocks on the M117 engines have an aluminum bore without steel liners and the engine block can be irreparably damaged if the wrong cleaning solutions are used or the wrong machining techniques are implemented. It’s important to make sure your shop has experience with these engines; Check references before proceeding.

While the engine block and heads were machined, I cleaned and painted the rest of the engine components, including the valve covers, oil pan and intake manifold. Rebuilding services for the alternator, water pump and a/c compressor are relatively inexpensive so I farmed that work out. Rebuilding the power-steering pump, on the other hand, is very easy, requiring just a few basic hand tools and about 30 minutes of work using a $35 rebuild kit from your local Mercedes-Benz dealer.

For the valve covers, I wanted to give the engine a 1960s custom look and feel, so I had the valve covers and intake manifolds smoothed and polished. Purists might disagree, but I was going for the look of the old Grossers from the 1930s and ’40s on which  Mercedes finished and polished everything under the hood.

With my machined engine parts ready for assembly and all the add-on components cleaned and painted, assembling the engine was pretty straightforward. The trick is to follow the book, be careful of tolerances and torques, and keep everything scrupulously clean.

Because I could devote three or four articles to the process of rebuilding a transmission, let me just discuss how I selected a good transmission for my project to mesh with my M117 V-8. In fact, rather than rebuilding the original ’60s 722 4-speed automatic, which is notorious for leaking oil, I decided to look for a transmission more suitable to the later engine I was using.

I didn’t want one of the sluggish 722.3 3-speed slush boxes from the 1970s, which in my book are lacking in both top-end and bottom-end grunt, and like the earlier trannies are not nearly as bullet-proof or reliable as the later 722.4s from the mid-1980s. These four-speed transmissions are reliable and can be leak-proof with very little effort. The 722.4 transmissions were designed so that they normally start off in second gear, but with a slight valve body modification they can be set up to start in first gear every time.

Because the only major difference between the M116 and M117 V-8s is that the latter had all-aluminum blocks whereas the former had cast-iron bottom ends, this means the transmissions are reasonably interchangeable between the different engines. Fortunately, I was able to find a Euro 500SEL that had severe cancer and was beyond practical restoration, but had a good working 722.4 transmission.

Now that I had my ideal power train set up I went about modifying them to fit in my Heckflosse, and that is for another day.
 

 
Part of the way through top-end assembly: Chrome valve covers and manifold in place.



Although not period-correct, I wanted to finish the engine to a high standard.



Besides, back in the 1930s, Mercedes-Benz finished and polished everything on high-end engines and transmissions. That is the look, and the standard, I was after. Side view of the completed engine.



 The engine mated to the transmission and front sub-assembly, ready for installation back into Heckflosse.