Can I change gear ratios?

[Tim2110]

I have a 96 Bayliner 1750 with a Merc 3.0 and an alpha 1 gen 2. After finding gear oil in the bilge, and no leaks in the reservoir hose I pulled the drive and found oil in the bellows. Next, I popped of the top cap and found the top bearing was toast.

This is an older boat, pretty rough. I found a used upper unit on line but it has a different gear ratio then my current 1.98:1. This one would be a 1.62:1. looks to be in good shape. My Question is: If I were to install this upper unit, mate it with my current lower unit, how would it change the performance of my boat? Lower top end? Pull an extra skier/tube? Fry the engine?
Thanks

 

[matt167]

Re: Can I change gear ratios?

That will not work well.. Pretty sure it will make an odd gear ratio. Doubt your boat will have much performance at all

 

[ktbarrentine]

Re: Can I change gear ratios?

If your upper end bearing was toast, more than likely (and in short time), your lower end will be toast, too unless you can be absolutely sure no bad oil from the bearing failure migrated to the lower (which it does). Not to mention the other fact that the lower gear ratio would require significant re-propping and just wouldn't be a good match for your motor. Should bite the bullet and go with a 1.98 SEI complete drive.
Best of luck.

 

[Tim2110]

Re: Can I change gear ratios?

That will not work well.. Pretty sure it will make an odd gear ratio. Doubt your boat will have much performance at all

I may be a newbie, BUT, this answer does not make sense to me. The engine drives the horizontal shaft to the upper case which then makes the rotation vertical - I am not changing the gears inside the upper case I am just changing their ratio. With changing the upper unit I am changing both the horizontal and vertical gearing together so they will continue to match. Now, the vertical shaft may be rotating faster or slower with this gear ratio then the previous gear ratio, that I expect. I don't see how that would change the prop dynamics, the prop will just be turning slower which means less speed. Please correct me if I am wrong.

 

[thumpar]

Re: Can I change gear ratios?

I may be a newbie, BUT, this answer does not make sense to me. The engine drives the horizontal shaft to the upper case which then makes the rotation vertical - I am not changing the gears inside the upper case I am just changing their ratio. With changing the upper unit I am changing both the horizontal and vertical gearing together so they will continue to match. Now, the vertical shaft may be rotating faster or slower with this gear ratio then the previous gear ratio, that I expect. I don't see how that would change the prop dynamics, the prop will just be turning slower which means less speed. Please correct me if I am wrong.

You would be lagging the motor. It would be like driving your car in 4th gear from a start. There is a reason there are different ratios.

 

[alldodge]

Re: Can I change gear ratios?

I may be a newbie, BUT, this answer does not make sense to me. The engine drives the horizontal shaft to the upper case which then makes the rotation vertical - I am not changing the gears inside the upper case I am just changing their ratio. With changing the upper unit I am changing both the horizontal and vertical gearing together so they will continue to match. Now, the vertical shaft may be rotating faster or slower with this gear ratio then the previous gear ratio, that I expect. I don't see how that would change the prop dynamics, the prop will just be turning slower which means less speed. Please correct me if I am wrong.

It will work and you will loose performance, that said; you will need to have your lower section inspected and be sure no problems exist. If your stuck on the cheapest way out go for it, as before it will work. You will need to reduce your prop pitch.

Or
sterndrive.cc SE116, UPPER 1.94 MODIFIED

 

[Tim2110]

Re: Can I change gear ratios?

It will work and you will loose performance, that said; you will need to have your lower section inspected and be sure no problems exist. If your stuck on the cheapest way out go for it, as before it will work. You will need to reduce your prop pitch.

So, it will work, the lower unit should be inspected and cleaned and I can compensate for the lost performance with a reduced prop pitch - currently I use a 21 pitch. Suggestions?Or
sterndrive.cc SE116, UPPER 1.94 MODIFIED

thanks

 

[Tim2110]

Re: Can I change gear ratios?

You would be lagging the motor. It would be like driving your car in 4th gear from a start. There is a reason there are different ratios.

Why are there different gear ratios? That would make sense if the prop adjusted like an airplane prop. Still the same number of RPMs from the engine. Right? A smaller motor like mine is on a smaller lighter boat. A V8 is used on a larger boat both run at the same/similar RPM. RPM and the pitch of the prop = water pushed = speed/power. Right?

 

[thumpar]

Re: Can I change gear ratios?

Why are there different gear ratios? That would make sense if the prop adjusted like an airplane prop. Still the same number of RPMs from the engine. Right? A smaller motor like mine is on a smaller lighter boat. A V8 is used on a larger boat both run at the same/similar RPM. RPM and the pitch of the prop = water pushed = speed/power. Right?

That is not how it works. If you look you will find that the ratios match the engine not the boat. The prop is only a slight adjustment to match the boat. If you run the wrong ratio and lug the motor you will ruin it. Whatever you run you should be able to get to proper WOT if you are under you are lugging the engine or there is a problem.