Dunno about OP, but old CAT bulldozers used to have smaller engines to start the...

Dennip 34 days ago | parent | context | favorite | on: How NASA brought the F-1 “moon rocket” engine back...

Dunno about OP, but old CAT bulldozers used to have smaller engines to start the main engine, before starter tech improved, iirc they were called "Pony engines(motors)"