The 560 is the ultimate M117 Engine.   This family of engines was introduced in 1969 with the 3.5l M116 and was followed in 1972 with the 4.5 M117.   The M117 is a longer stroke version of the M116.   Both engines share a SOHC design, 2 valves per cylinder and always had fuel injection.

These engines evolved over time with the final iteration coming between 1985 and 1991.  The 560 was the largest M117 engine offered, although to be pedantic it is actually 5.5 litres.

The story goes that Mercedes-Benz were concerned that the introduction of the BMW E32 7 series with its 220KW V12 placed the W126 at a competitive disadvantage.    The W140 was apparently delayed to respond with a V12 and the 560 was a short term competitive response.  The 560 is a longer stroke version of the 500.   At the same time larger valves were also specified.  The 560 offers more power than the 500, although the 500 has the reputation of being the smoother engine.

To meet the E32’s specs a high Output version of the 560 engine was offered with 220kW.  This engine had a raised 10:1 compression ratio, different cams, ignition timing and an improved exhaust system.  It was coupled with a 2.65:1 rear end, allowing it to outperform the E32.   The 2.65 contrasts with the 2.24 ratio used on the 500, and the 2.47 used on the 420.   At first, the high output version was an option, code 822.   It was offered from 10/1985-9/1987 and known as the ECE version.   My 1987 560SEC is the code 822/ECE version.

The ECE version was a start, but more and more markets in Europe required a catalytic converter.   Mercedes offered two versions for this case.   The KAT version had 180kW and had the Catalyst fitted as standard.  The RUF version was set up to allow the catalyst to be retrofitted later and had 200KW.   Both of these versions ran the standard 9:1 compression.

Mercedes still faced a challenge against the E32.   Many European markets required the RUF or KAT version.   Therefore, from 9/87 the RUF and KAT versions were revised.   Compression was raised to 10:1 and other changes introduced, such as knock sensors to retard the timing when necessary.    This made the ECE version redundant, as the RUF version now also had 220KW.  The RUF version could still be retrofitted with a catalyst.    The KAT version now had 205KW, a useful improvement.  While not the subject of this article, the compression ratio changes were also applied to the 420 and 500 engines, providing a useful power boost.  The 10:1 engines either have HV or E10.0 after their engine numbers.

The 560 engine also offered an opportunity to provide more performance in markets with strict emissions laws.   The larger motor still allowed good performance even when de-tuned for idle emissions.    This was particularly important in the all important US market.    The 1984-85 500SEL in US spec only managed 137kW.   The move to the 560 allowed power to be raised to 178-180kW depending on market.   My 1988 and 1989 560SECs were both this version.   One particularly restrictive element of this 560SEC is the exhaust system.   There is a crossover pipe that joins the output of both banks of cylinders into a single catalyst.     The primary destination of this 560 was the USA, but it also formed the basis of the Australian and Japanese versions, with minor changes.  This version of the 560 was equipped with a 2.47:1 rear end instead of the 2.65 used in other 560s.

Unlike the other 560 engines, the emissions version never had the compression ratio revisions.   It was the same story with the 420.  The rest of world 420 had the compression rise but the emissions version did not.

It was this emissions engine that was the only 560 available in the R107.   The 560SL was only offered in Australia, USA and Japan.   It was slightly lower in power than the W126 version as the exhaust was more restricted.     This is why it has less powerful than the contemporary 500SL.   The big advantage of the emissions engine is that it can run lower octane (91) petrol.

The differences between the engine types are extensive:

Exhaust

The high output versions had ‘tri-y’ exhaust headers.   Essentially the tri-y setup consisted of four piece manifolds that joined under the car into a dual exhaust system next to the transmission.   The mid output versions had ‘euro log’ exhaust headers which was a single manifold for each side, each with a pipe under the car to the exhaust system. When catalysts were fitted, there were two.   The final option was the restrictive system where a crossover pipe behind the engine linked the two manifolds together to enter the single catalytic converter.    The KAT/RUF cars have an oxygen sensor.

The engine photo clearly shows the exhaust manifold from the ‘tri-y’ setup.

Ignition

All models used EZL based ignition, but the map was different.   The mid and high output models had a switch to allow the engine to be de-tuned for poor fuel.    The emissions controlled models were not switchable.    The high output motors have a more advanced ignition, and the later (post 9/87) cars have knock sensors.   As the early ECE versions do not, they require 98 octane fuel.

Camshafts

High output engines hav different camshafts with ECE, RUF and KAT camshafts all having different part numbers.

The ECE Camshafts have code 16/17 (Left/Right).   RUF are 24/25 and USA is 26/27.    The ECE and RUF cams have the same profile.

Other

• The strict emissions version has an air pump.
• The high output motors also have a different fuel distributor.
• All 10:1 compression engines have high compression pistons.
• The high output models have a separate oil cooler and pump.   This is located at the front left of the car.
• High output models have a different (black) transmission modulator
• Transmissions were the same on all models.   Starting with the 722.323 and then later the 722.350.   The .350 transmission was improved over the 323.

Unlike other engines, all versions of the 560 are good.   Even the emissions versions have plenty of power and are a delight to drive.   The M117 has an almost bullet proof bottom end, but an Achilles heel in some plastic parts in the engine.  If these parts fail, it is not economically viable to fix the engine.

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