AMC 4.2-Liter
The venerable AMC six-cylinder was in production for an unbelievable 50 years and has outlived its parent company. It started as an economic engine with smaller displacement and decent power and managed to be the best engine option in numerous AMC and Jeep models (via Jeep Tech).
The 4.2-liter had outdated construction, but it was an insanely dependable motor. Overall, it required low maintenance and could run on low-octane fuel. During the ’70s, it was common on AMC models. But with low compression, it had only about 120 HP, which was a ridiculously underpowered figure.