Force Propeller change

[fishbait2]

I have a Force 1989 125hp . Changed gear case and it’s a little different. Old is single exhaust and gear ratio of 1.73. New gear case seems to be a 1991 or 2 Type B
with thru exhaust. I believe it has a gear ratio of 1.93:1 .
I was told it came off a 1989 Force 125hp. It may have but I believe it’s from a 150 or 120hp. And everything I am researching suggest it has a 1.93:1 gear ratio. So the motor is one of two on a 89 2302 and I need to match as close as possible the original prop set up of the original outboard gear case. I had a 13x19 from factory Force prop , but with the changes now what size prop would I need to match the old set up motor and gear case ratio?

 

[jerryjerry05]

The only way to check the pitch: take it for a wide open run and check the rpm's.
I think the 89/125 ran at 5500 wot.
If your getting 5500 with the setup you have??? then no change needed.
Say 5k is the max? then drop down in pitch, say from a 19 to a 17.
6K then go up in pitch. From a 17 to a 19

 

[fishbait2]

Thanks for the reply Jerry, trying to figure this out with twin motors on the boat. Yes it was around 5500 rpms per motor. Question on checking on the correct prop, with the twin motors how can I tell if the motor with the different gear ratio is pushing equally between the two?

 

[jerryjerry05]

That would only happen if the gear ratio was the same in both lowers.

Google, utube checking gear ratio on Force outboards.


Might have to take them apart and count teeth?

Top of each drive. along the top is factory letters and #s that denote the ratio's\.
Real close pics of any letters or numbers.
The OEM manual has info on ratios and gear settings.

The 88/89 should be the same ratio.


2.21 193-1 was used in the 90-94 depending on the ABCD model??
You'll have to find the breakdown to see which is used.

 

[fishbait2]

I found the schematic on the gear case of ABCD.
It appears to match type B. Making me believe it's a 90 gear case. I also found a post that said to mark the prop center blade, pull spark plugs and kill switch at dash and disconnect the battery. Manually move the top flywheel clockwise and have a helper put the motor in forward gear. Continue to turn until a prop blade is at 12pm Center blade mark. Then mark top flywheel and turn clock wise three times ending at the start mark. The blade will turn and end at either 4 , 6, or 9 as looking at a clock. If at 6 or 7 it's 1. 93 if at 9 it's 1.73. But I am guessing it will be a 1.93.
Another post talks about an 85hp used on a 125hp and would need a pitch change on the 125hp prop to increase by two. So as to match the 125 original set up.
So if this is all true it sounds as though I would need to increase the 1.93 replacement gear case prop by two higher pitch from 19 to 21. Just trying to link all the info
but I don't know if I am thinking correctly on this.

 

[Nordin]

Yes checking the gear ratio is simple by checking how far the prop will turn when turning the flywheel one turn.
For a example gear ratio 2:1 says that 2 turn of the flywheel will turn the prop 1 turn.
1,93:1 will give you 1 turn of the prop when flywheel is turned 1,93 turn and for a 1:73 it is 1,73 turn of the flywheel.

 

[fishbait2]

Excellent! being that I still have one motor with the original set up gear ratio I can check both at the same time and compare movement. I will give you an update as soon as I test both.