Transmission gear ratio for new prop

[Peter17970]

I have a 1987 O'Day 322 and need to get a new prop. Boat came with a 3 bladed prop but did not have the right pitch and can not be repitched. I need the gear ratio for the transmission in order to complete the prop sizing form. The boat has a standard 2GM20F Yanmar and the transmission looks like it is the original one. The Yanmar documentation indicate there could be 3 different gear ratios for the 2GM20F engine. I checked the transmission through the quarter berth access doors, but I did not see any label indicating the Thanks

 

[J.B. Dyer]

Try this!

Morning Peter:If all other attempt's fail, try this. Put a mark on the harmonic balancer (main crank shaft pully) of the engine and pull the compression release. Put a mark on the prop shaft. Turn the engine over by hand and see how many revolutions of the engine it takes to make one complete turn of the prop shaft. That should give you some idea of what to compare with the known ratios. Like three complete engine revolutions to one prop shaft revolution = 3:1, etc. Oh yeah, make sure the switch is off and the key is in your pocket just for safety's sake.Luck!