While I have the lower unit off...?

[tonyjh63]

Ok, so I may be changing my impeller soon, and was wondering if I would be able to count the teeth and get a definitive answer as to what my drive ratio is while the lower unit is off? Also, why do these impellers need changing so often? Thanks!

P.S. Forgot to mention, it's a Alpha One, Gen 2

 

[GA_Boater]

Don't know about counting teeth, but impellers wear because rubber rubs against a stainless cup and wear plate with a mix of water, silt and sand. And the rubber hardens, losing it's flexibility.

Why are they changed so often? Because an ounce of prevention is worth a pound of cure. Actually it's worth buckets of money if the impeller fails, the motor overheats and is damaged.

 

[thumpar]

You can count the teeth with the drive on or easier would be to turn the engine over until the prop turns once and see how much turning it takes.

While the drive is off check bellows very closely. Check alignment. Feel the gimbal bearing for smoothness. Lube the u-joints if they can be.

Lose an impeller while on the water and you will know why you change the impellers so often. I lost one a few years ago. It was a new to me boat and just wanted to finish out the season. I was really good about changing it on my previous boat but didn't take the time.

This year I changed it again after 3 season. It still looked good and had no cracks. I will change it again at the same schedule even though it may go longer. This is a Bravo so different impeller and not sure on the Gen II lifespan.

 

[scoflaw]

When the drive is off, rotate the prop shaft 1 turn while observing how much the input shaft turns

 

[tonyjh63]

Thumpar - how do you count the teeth with the drive on?
Scoflaw - know where I can find diagrams/pics, so I'll know where the prop shaft and imput shafts are? I'm very new to all this (have never even seen the inside of a drive unit), and not very mechanically inclined.
Thanks everyone for the responses!

 

[nola mike]

The input shaft is the one with the u joints on it. The prop shaft is, well, attached to the prop. You can count the gears by removing the top cover of the drive held on with 4 12 point bolts.

 

[thumpar]

Thumpar - how do you count the teeth with the drive on?
Scoflaw - know where I can find diagrams/pics, so I'll know where the prop shaft and imput shafts are? I'm very new to all this (have never even seen the inside of a drive unit), and not very mechanically inclined.
Thanks everyone for the responses!

I told you how in the post. You turn the motor (by hand) until the prop turns one time. If you have to turn the motor 1.98 times to get the prop to turn once you have a 1.98:1 if it only takes 1.5 turns you have a 1.5:1. Mark things well and you will have your ratio.

 

[scoflaw]

If the drive is coming off, it would be easier then to rotate the prop shaft

 

[tonyjh63]

Thumpar - I thought you meant that I could count the teeth with the drive still on...
Btw folks, when we say "the drive is off", we are talking about just the very lower part that comes off when you replace the impeller, right? Thanks again!

 

[H20Rat]

Thumpar - I thought you meant that I could count the teeth with the drive still on...
Btw folks, when we say "the drive is off", we are talking about just the very lower part that comes off when you replace the impeller, right? Thanks again!

Nope, it is easier to pull off the entire upper and lower as a unit. Only a couple bolts and it pops off, 5 minutes or less if you are experienced. You need the entire thing off to get to the driveshaft/gimbal bearing/ujoint, as well as check alignment. Just make sure the shifter is in forwards for both removal and re-install.

 

[thumpar]

Can't do much other than change the impeller with just the lower off. I would suggest pulling the whole drive. It will be easier in the long run. If you want to count the actual teeth you will have to take the top cap off the drive. That can be done on the boat. I would figure out the ratio by turns though, either on or off the boat.