Part number LIT-11616-YF-25 puts the 1989, 1990 and 1991 MOTO-4 250 machines into one service volume, and the MOTO-4 with them. The 1989 model is coded YFM250W.
This is the dealer text, so it does not skip the measuring. Pistons, bores, valve stems and guides, shift forks, brake friction material and drive components each come with a nominal dimension and the limit past which the part is scrap. That is the difference between reassembling an engine and hoping.
You also get the periodic maintenance schedule, torque tables, exploded views and the complete harness diagram. Check YFM250W against the label on your frame before ordering parts or setting a clearance, because the three years in this book are not identical everywhere.
