How to determine gear ratio?

[at100plus]

How do I determine the gear ration on my lower unit? Previous owner didn't know....

[transomstand]

Mark the propshaft, rotate the flywheel 2 turns while observing propshaft. If the propshaft rotates twice, and ends up on the same mark, you're 2-1, if it goes a little beyond the original mark(about 1 o'clock), it's 1.87-1.

[at100plus]

Thanks Pete, its off the boat but I assume marking the top of the shaft will work the same.

[HStream1]

With the lower unit on the Mid or Off?

Either way it's pretty simple.

1.72 would be 1 & 3/4 revolution on the flywheel or drive shaft to 1 revolution on the prop shaft. example: One complete revolution then rotate to 9 "o"clock.

1.87 would be 1 & 7/8 revolution on the flywheel or drive shaft to 1 revolution on the prop shaft. example: One complete revolution then rotate to 11 "o" clock.

2:1 is self explanatory.

[BagMan]

With the lower off, my sportmaster is stamped 1.87 on the top inside lip. Don't know if they're all stamped though.

[at100plus]

Pretty simple. Don't know how this basic figure slipped by me in 25 yrs of boating. Duh 2 turns driveshaft = 1 turn propshaft hence 2:1

[rock]

When the light finally comes on it's almost like you invented it.
Rock

[at100plus]

:cheers:totally