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The R107’s V8s come in two families: the M116 and the M117. They share a basic design but differ in size, and the model on the trunk lid does not always tell you which version is under the hood.
Which cars got each
| Engine family | Displacements | R107/C107 examples |
|---|---|---|
| M116 | 3.5, 3.8, 4.2 liters | 350SL/SLC (Euro), 380SL/SLC, 420SL (Euro) |
| M117 | 4.5, 5.0, 5.6 liters | 450SL/SLC, 450SLC 5.0, 500SL/SLC, 560SL |
The US 1972 “350SL” actually had the 4.5-liter M117, which is why it was renamed 450SL for 1973. Always confirm with the engine number.
Displacements and bores
Both families use a single overhead cam per bank. The M117 uses a larger bore and, in its later versions, longer stroke. From around 1980, Mercedes introduced lighter aluminum-block versions (3.8 M116 and 5.0 M117) using a special silicon-alloy bore surface instead of cast iron liners.
Shared parts
Many parts interchange or are similar between the two families: cam followers, valve train parts, many sensors, some seals and gaskets, and much of the ignition and fuel injection hardware, depending on year. Pistons, rods, cranks, heads and blocks differ. Use the engine number when ordering; see parts interchange.
Timing chain differences
The early aluminum 3.8 M116 used in the 1981–83 380SL had a single-row timing chain that is known to fail; most were converted to double-row. Other R107 V8s use double-row chains. All of them need guide rails and tensioner checks with age. See 380SL timing chain and timing chain interval.
Which is stronger
The M117 makes more power and torque because of its size. The 560SL’s 5.6 is the strongest US version. The M116 is lighter and slightly more economical. Both are durable when maintained, and reliability depends far more on chain, cooling and maintenance history than on which family you have. More in M117 engine and M116 engine.
Engine code location
The engine number is stamped on the engine block and recorded on the car’s data card. The first digits identify the type, for example 116.9xx or 117.9xx. If the number does not match the data card, the engine has been replaced, which matters for value.
Quick answers
- Can I put an M117 into a 380SL? It has been done; engine mounts, wiring, fuel injection and transmission compatibility all need planning. See engine swap options.
- Is the 380SL’s M116 a bad engine? No. Once it has a double-row chain and sound guides, the 3.8 is a durable engine. The chain history is the key question when buying.
- Which is cheaper to maintain? Running costs are similar; both use similar service parts. The bigger cost differences come from condition and history.
- Does the aluminum block need special care? Use the correct coolant and keep it fresh to protect aluminum surfaces, and keep the cooling system healthy. See coolant.
