Lower unit Gear ratios?

[tater76]

Hi folks, so I am curious if my 1973 Chrysler 55hp has the same gear ratio as my 1985 Force 50hp motor? I can't seem to locate this in the manual (I might be blind?). They look to be interchangeable, but I am thinking if the 50 has a better ratio for my boat I may just swap it on.

 

[Robbabob]

Re: Lower unit Gear ratios?

I am told there is a stamping on the lower unit with the ratio.. might be something like just 1.47 or 1.68

For the life of me, I can't find it on mine. Only found a little tag with nothing on it. LOL

Good luck!

 

[tater76]

Re: Lower unit Gear ratios?

Thanks Robb, I will look them over in a minute and post what I find

 

[tater76]

Re: Lower unit Gear ratios?

Well, I did not see any markings at all I guess we will have to wait for Frank or Jerry to chime in

 

[Frank Acampora]

Re: Lower unit Gear ratios?

I THINK--don't quote me on this that the ratio for the Chrysler 35, 45, and 55 was 12 to 21. It was the same ratio for all three engines and different pitched props were used. Bore and stroke were different and horsepower was developed at a different RPM for each engine.

I would not be surprised if the 1980s Force 50 has the same ratio because Merc had not started making major changes to these engines yet and it uses the same props. I have not torn one apart yet so I can't say for sure though.

If you get your hands on a lower unit, turn the driveshaft twice and see how many revolutions the prop shaft makes.

 

[tater76]

Re: Lower unit Gear ratios?

Thanks Frank, I will look at the 50 lower this afternoon, and post the results.