I've been searching around for over a year, for a service manual for the three-cylinder Hercules 130 cubic inch diesel - model DD 130. It's in my Oliver OC4 crawler. I do have the Oliver tech manual that gives some basic engine info. But, I'd like to find a more detailed engine book. Been quite surprised that I haven't come across any. I've checked the usual sources including Zimmermans, and just about all places I know of that deal in manuals, including two Hercules Websites. The gas version is easy to find books on (GO 130). There were some bigger versions of the DD 130, e.g. the DD 149, and the six-cylinder version the DD 260. I haven't found any books for them either. Seems Hercules must of had a service manual at one time for this thing.