From one review:
The kit has nice components. The instructions are complete (24 pages in Japanese). And, there are a whole bunch of tiny details to get lost in. The cylinder mount and the gears need to be carefully aligned. This is one of the trickier parts. If you have it misaligned, there will be too much friction for the engine to run. A gauge is supplied to make this step easier.
This and several other hard-to-find Gakken kits can be found at the Make Magazine MakerShed.