The Caterpillar 'D' series

The Caterpillar 'D' series of the 6.25" bore engines is probably the most successful and longest running production engine to date made by Cat. Its' relative simplicity and complete mechanical control made it a popular choice for many equipment manufacturers, ship builders, drill rigs, off-highway trucks and electric power generation around the world. These engines were available in both diesel and natural gas fuel and were all 4-stroke cycle. The six, eight, twelve and sixteen cylinder versions of this engine shared many common internal components with the later three being V-configuration. All of these engines operated at a maximum rpm of 1200 and they developed 70bhp per cylinder upon their initial release.

The series started in 1957 with the in-line 6-cylinder engine model D353 and horsepower starting at 420 at 1200rpm.In 1961 the Caterpillar D379 rated at 560hp, in 1962 the model D398 rated at 850hp and finally in 1967 the 16-cylinder D399 was released and rated at 1120hp. The product line was constantly being improved by Caterpillar engineers and the actual horsepower ratings increased with the improvements. The 6.25" bore engines enjoyed success for almost 33 years when they were discontinued in 1990 and replaced by the 3500 series family. The 'B' version of this series was implemented in approximately 1979-1980 with the revised and angled connecting rod caps which greatly facilitated the disassembly and field service of the engine. A common misconception people have with serial numbers is the letter 'B' within the serial number. This did not represent the later version of the engine as the difference was in the serial number itself. Each engine model had a unique prefix that identified the general application that the engine was intended for when it was manufactured. But over the years there has been conversion by owners from one industry to another, a sign of the engine's versatility. Please see our serial number prefix identification chart here.

The 6.25" bore family of engines still enjoys immense success worldwide even after being out of production for over 18 years. It is especially popular overseas and in third world countries where emission standards are much lower than in the US and where operators may not have the knowledge or financial resources to take care of a more complex 4-stroke diesel engine. Their bullet proof design lets them keep going and going with minimal maintenance. 35-40,000 hours between rebuilds is common with reasonable maintenance. Caterpillar offers premium service around the globe at hundreds of dealers and distributors as well as many quality aftermarket sources.

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