If it's an old Yale built in Japan, it will most likely have a Mazda VA engine. 2 litre capacity, built from the early 1970's to about 1982. They're a good engine, they've got replaceable cylinder liners, but the parts are getting harder to find for them. I've got a similar forklift and I'm rebuilding the engine, I had to get the liners from Taiwan. I've got some spare new liners if you need some.