For owners and enthusiasts of classic Mercedes-Benz vehicles, particularly the 1968 models, understanding engine compatibility is crucial for maintenance, restoration, and performance upgrades. This guide focuses on the engine specifics for the 1968 Mercedes, drawing on expert knowledge to clarify engine interchangeability and modifications.
Interchangeability of the 250 Engine (1965-1969)
The foundational 250 engine block remained consistent across Mercedes models from 1965 to 1969. This means that for a 1968 Mercedes, the core 250 engine assembly from any model within this range should be compatible. Whether you’re dealing with a standard 250 or a 250SE, the engine block itself offers a degree of interchangeability.
However, it’s important to note distinctions, especially when considering the 250SE engine used from 1965-1968. While the 250SE engine can be utilized, it necessitates swapping the motor mounts. These mounts are unique to the 250SE and differ from those used in the standard 250 models. Therefore, if opting for a 250SE engine for your 1968 Mercedes, ensure you acquire the corresponding motor mounts for a seamless installation.
Short Block Considerations for 1968 Mercedes
Focusing on the short block—the engine block and internal components without the cylinder head—the compatibility widens. Any 250 short block, regardless of whether it originated from an ‘S’ or ‘SE’ model, and from any year between 1965 and 1968, should be suitable for your 1968 Mercedes. This offers flexibility when sourcing replacement parts or undertaking engine rebuilding projects.
Locating a short block specifically designed for a Fuel Injection (FI) engine at a reasonable price, however, might present a challenge. While physically compatible, the demand and potential rarity of FI-specific short blocks can influence their availability and cost on the market.
Automatic vs. Manual Transmission Blocks
A critical point to consider for 1968 Mercedes engine work is the differentiation between automatic and standard (manual) transmission engine blocks. These are not interchangeable. While the exact reasons aren’t explicitly detailed in all manuals, it’s strongly believed to relate to the flywheel and crankshaft assembly.
Mercedes balanced the crankshaft and flywheel as a unified component. This integrated balancing approach means that simply bolting on a different flywheel is not advisable. The implications of this balancing act are significant enough to render automatic and manual blocks incompatible. Interestingly, this balancing philosophy also explains Mercedes’ use of ring gears in many engines of this era. Instead of replacing the entire flywheel or flexplate when the teeth wore down, only the ring gear with the teeth needed replacement, showcasing a sophisticated engineering approach to component longevity.
Converting to Fuel Injection in a 1968 Mercedes
For those considering upgrading a 1968 Mercedes to Fuel Injection (FI), it’s a more involved process than a simple engine swap. A complete engine, including intake and exhaust manifolds, is necessary. Furthermore, the fuel system demands attention. An electric fuel pump is essential for FI, and while original rebuilt pumps can be costly, aftermarket options delivering approximately 42 psi of working pressure are available and more budget-friendly.
Beyond the fuel pump, a fuel pressure regulator is also mandatory. This regulator maintains the required 42 psi, returning excess fuel to the tank and ensuring consistent fuel delivery for the injection system.
Wiring and Ancillary System Differences
Implementing Fuel Injection introduces notable wiring complexities. FI engines incorporate components absent in carbureted versions, such as a throttle position sensor and a thermotime switch. These sensors and switches require corresponding wiring and potentially ECU (Engine Control Unit) considerations depending on the specific FI system being implemented.
Moreover, the Air Conditioning (AC) mounting points also differ between FI and carbureted engines. This can add another layer of complexity if your 1968 Mercedes is equipped with AC and you’re undertaking an FI conversion.
In conclusion, understanding the nuances of engine compatibility for your 1968 Mercedes, particularly concerning the 250 engine series, is vital for any repair, restoration, or modification project. While core components offer interchangeability, specific differences like motor mounts, transmission block types, and the complexities of Fuel Injection conversions must be carefully considered to ensure a successful outcome.
