Gear ratio ID Help

[sebas54]

Hi, I have a 1987 4.3l GM Merc I/O Alpha I. I am trying to figure out what gear ratio I have. These are the numbers that I found on the outdrive: A415189 D

I was told that I may have the wrong gear ratio because I am lacking in speed and RPM's. I have a 15x15 prop and WOT is 4500 RPM's with max speed of 27 MPH.

Thanks.

 

[sebas54]

Re: Gear ratio ID Help

Do these numbers mean anything?

 

[ShaneCarroll]

Re: Gear ratio ID Help

To find your gear ratio, go to the Adults Only Sticky at the top of the Mercruiser forum, and there is a link in one of the manuals that will tell you the ratio by the serial number.

 

[Don S]

Re: Gear ratio ID Help

To find your gear ratio, go to the Adults Only Sticky at the top of the Mercruiser forum, and there is a link in one of the manuals that will tell you the ratio by the serial number.

There isn't anything to tell you what the gear ratio is by SN. SN range yes, but not exact number. You will find that different ratios are in the same ranges.

Best thing to do to find the ratio is to turn the engine by hand and count how many turns the engine turns (by hand) to turn the prop one full revolution

1.5 turns = 1.5: 1 gear ratio.
2 full turns is a 1.98: 1 gear ratio

There is also a gear ratio stamped on the port side of the drive in the same section of the drive as the SN. Assuming that no one changed gears in it since new. Could easily have a high altitude gear in it.

 

[sebas54]

Re: Gear ratio ID Help

Thanks for the reply so obviously I will need someone to watch the prop while I turn the engine?

 

[Bondo]

Re: Gear ratio ID Help

Ayuh,... Use Paint Marks,+ a Wrench,... Not the Starter....