Alpha Gen2 2.0 lower unit differences?!

[bigcanoe]

I get different stories depending on the tech I talk to regarding the lower units for the 2.0 ratio drive. Some say there's a difference, and advertise their lower as being specific for the 2.0 upper, others say no difference. So... can anyone say definitively, that there is NO difference in the lower from ratio to ratio on the Gen2 Alpha 1? Especially since I got a screaming deal on a new lower that I have no idea which upper it "belongs" too.

 

[Don S]

Re: Alpha Gen2 2.0 lower unit differences?!

There are differences, just not that you can see. The uppers and lowers have different gear ratios.
For example, your 2.0 ratio LOWER has 14-28 tooth count, while the 1.98 would have 17-28
The 2.0 upper would have a 24-24 tooth count vs the 1.98 that has a 20 drive-24 driven tooth count.

Here is a chart from the OEM manual that shows the different tooth counts for different ratio's.

 

[bigcanoe]

Re: Alpha Gen2 2.0 lower unit differences?!

Any way to tell which lower is which? (other than counting gears). And , of course, the "any lower unit will work" statement is out the window. I now have a new lower that I may not be able to use... great.

 

[wca_tim]

Re: Alpha Gen2 2.0 lower unit differences?!

UNless I'm confused, if it is a gen 3 lower, it is the same, the difference is in the upper

 

[cr2k]

Re: Alpha Gen2 2.0 lower unit differences?!

Gen III??? You mean Bravo III?

 

[NHGuy]

Re: Alpha Gen2 2.0 lower unit differences?!

Hey bigcanoe. You can use either of those ratios. a 1.98 is so close to a 2.0 that it does not matter. If you have a different lower post it up and someone in the know will give you the math. Or you can look it up on the chart if it's on there.
If you have a ratio that's wrong you could resell the drive that you got on such a great deal.

 

[Don S]

Re: Alpha Gen2 2.0 lower unit differences?!

Any way to tell which lower is which? (other than counting gears). And , of course, the "any lower unit will work" statement is out the window. I now have a new lower that I may not be able to use... great.

To check just the lower unit ratio without taking it apart, Put it in forward gear by turning the shift shaft straight forward while turning vertical shaft clockwise to make sure it's in gear. Once all the slop is out of the gears, mark the prop shaft and turn the vertical shaft exactly 2 turns. If the prop shaft turns 1 complete revolution it's a 2.0 lower with 14/28 gear tooth count, if the prop shaft only turns about 3/4 turn, you have a standard lower with 17/28 gear tooth count.

Oh, and there is no such thing as a Gen III drive.

What ratio drive do you have on your boat to begin with? You have yet so say what engine and drive setup you have.

 

[wca_tim]

Re: Alpha Gen2 2.0 lower unit differences?!

My apologies on the fat fingers and tired eyes of last night. I intended to say if it's a gen 2...

What I intended to say was that My understanding is that you're only talking about the lower half of the drive - if that is the case, the gear ratios are similarenough that you should be able to get away with either lower. The largest difference in gear ratios comes from the gears in the upper half of the drive. Again, sorry for the typo and not reading carefully... Hope this is helpful.

 

[bigcanoe]

Re: Alpha Gen2 2.0 lower unit differences?!

My mistake on the engine and drive ratio. It's a 3.0 with the 2.00:1 upper unit. The upright shaft on my old lower snapped in 1/2. I now have a new lower unit, but have done "triage" on the upper and the bearings are shot. It's amazing how fast things go bad. I shut it down immediately after the break, but it got hot enough to do some damage. the sucky part is that there are less than 80 hours on the boat.

 

[Don S]

Re: Alpha Gen2 2.0 lower unit differences?!

My mistake on the engine and drive ratio. It's a 3.0 with the 2.00:1 upper unit.

So what's the problem. IF you bought a 2.0 lower, all you need is a 2.0 Upper to go with it

 

[bigcanoe]

Re: Alpha Gen2 2.0 lower unit differences?!

I got a screaming deal because lower was "unidentified" as to which ratio it has. It was a crap shoot, but too good to pass up ($405 delivered to my door). Just trying to cover all my bases and not just throw it together and hope it lasts.

 

[Don S]

Re: Alpha Gen2 2.0 lower unit differences?!

Just check the amount of rotation as I explained above. If you have the wrong gears in the lower, you will end up with a 1.62:1 ratio which won't work for your 3.0L engine.

 

[bigcanoe]

Re: Alpha Gen2 2.0 lower unit differences?!

So... 2 turns of vertical shaft = 1.25 turns of propshaft. Your thoughts? Also, thanks for all the previous help. Very informative.

 

[Don S]

Re: Alpha Gen2 2.0 lower unit differences?!

So... 2 turns of vertical shaft = 1.25 turns of propshaft. Your thoughts? Also, thanks for all the previous help. Very informative.

You have a 17/28 tooth count on the lower. I was backwards in my explanation before, I think. There are only 2 choices and it's not 2;1
With your 2.0 upper, you now have a 1.62/1.65. Not what you want.

Here ya go, you can do the math. Makes my head hurt :facepalm: