2.00 ratio Alpha one gen 2

[Mercperk]

Couple of questions;
Generally, what is the whole point of 2.00 ratio?
Efficiency? Engine wear? What's it's deal?
Why would you put it on a 3.0l instead of the 1.94?

The talking specifically about the gearcase what is the difference between the 2.00 ratio and the rest of the gearcases?
Just the gear set or is also the housing?
Thank you for your consideration I hope I was clear I've got COVID yay!

 

[achris]

Couple of questions;
Generally, what is the whole point of 2.00 ratio?
Efficiency? Engine wear? What's it's deal?
Why would you put it on a 3.0l instead of the 1.94?

The philosophy of different ratios is to do with the target boat size for a given engine size. The idea is to keep the propeller for each boat/expected engine in the 15 to 23 inch range.
In theory you could run all engines on the one ratio, say 1.65:1, but that would mean a very short prop (around 11" on a 3 litre engine and a very tall prop on the big V8s (probably in the order of 27" or more). That would mean a huge inventory for the prop makers... THAT is inefficient...

The talking specifically about the gearcase what is the difference between the 2.00 ratio and the rest of the gearcases?
Just the gear set or is also the housing?

All the housings are the same, regardless of ratio.
Another thing to consider is the 'hunting' of gearsets. A nice even number like that with be a fully hunting gearset, meaning that certain teeth on one gear only ever mesh with limited numbers of teeth on the other gear. That means a few issues to consider. Harmonics is one, another is if the housing is ever disassembled, it MUST be reassembled with the same teeth matched, and a lot of people just throw gears back in and not consider match-marks... The 1.65:1 gear set in the upper is a 24:24 tooth set, and is a fully hunting gearset. Number of those boxes I've pulled apart, usually for 'noisy gears' and found the match marks don't match.... Throw the gears in the bin and buy new ones. And then assemble them matched up!

Thank you for your consideration I hope I was clear I've got COVID yay!

Plenty clear. Hope you're vaccinated, and recover quickly.

Chris....

 

[Scott Danforth]

for the A1G2

1.94:1 is whats available, however close enough to 2:1 for the 3.0 that its called 2:1
V6's and small V8's at altitude get the 1.62:1 to a 1.81
typical 5.7 and 6.2 V8's get a 1.47

 

[Mercperk]

Thanks for the info.
Okay after much digestion I see what your saying.
Is there any way to determine gear set in a gearcase without pulling it apart? Probably with a dial of some sort and beyond my ability....

And if I'm understanding properly, there should be no problem taking all of the guts out of a worn alpha one gen 2 2.00 ratio gearcase housing, races and shims included, and put them into a nicer alpha one gen 2 unknown ratio gearcase housing?
And I wouldn't run into any issues I'd just have to reshim or not reshim?
Thank again folks
Fully vaccinated I honestly just feel inebriated very strange and cloudy

 

[Bondo]

And if I'm understanding properly, there should be no problem taking all of the guts out of a worn alpha one gen 2 2.00 ratio gearcase housing, races and shims included, and put them into a nicer alpha one gen 2 unknown ratio gearcase housing?
And I wouldn't run into any issues I'd just have to reshim or not reshim?
Thank again folks
Fully vaccinated I honestly just feel inebriated very strange and cloudy

Nope,...... Not at All right,.... Quite the opposite,......

Unit, for unit, they'll swap just fine,.....
Guts to a different case is called a Rebuild, with all the sequences to get there,.....

 

[achris]

Thanks for the info.
Okay after much digestion I see what your saying.
Is there any way to determine gear set in a gearcase without pulling it apart? Probably with a dial of some sort and beyond my ability....

Mark the input yoke and the prop shaft, then start turning the yoke (counting the turns as you go) until the prop shaft turns 10 times. You have your ratio. If the yoke needed 18 1/2 turns for 10 turns of the prop shaft, then it's a 1.84:1 ratio... Simples.

And if I'm understanding properly, there should be no problem taking all of the guts out of a worn alpha one gen 2 2.00 ratio gearcase housing, races and shims included, and put them into a nicer alpha one gen 2 unknown ratio gearcase housing?

And I wouldn't run into any issues I'd just have to reshim or not reshim?

Moving anything from one gear case to another will always need a reshim. Always. Gearcases are cast and as such they will vary from one to another, hence shims.

Thank again folks
Fully vaccinated I honestly just feel inebriated very strange and cloudy

Best wishes.

Chris....

 

[QBhoy]

Think the gear ratios with tiny difference are to do with age and drive type too. As in, I think 1.47 ratios in alpha were along side 1.5 ratios in bravo and maybe older alpha may have been 1.5 ?? Not sure.
But I know 3.0 had a couple of ratios. So did 4.3’s and so did 5.0’s etc etc. Altitude and the particular boat they were installed on also had a fair bit to do with things too.
I have a 5.0 v8 with a 1.47r. I’d imagine most on here would either think that extremely unusual or unlikely…but it’s true, nonetheless

 

[achris]

Think the gear ratios with tiny difference are to do with age and drive type too. As in, I think 1.47 ratios in alpha were along side 1.5 ratios in bravo and maybe older alpha may have been 1.5 ?? Not sure.
But I know 3.0 had a couple of ratios. So did 4.3’s and so did 5.0’s etc etc. Altitude and the particular boat they were installed on also had a fair bit to do with things too.
I have a 5.0 v8 with a 1.47r. I’d imagine most on here would either think that extremely unusual or unlikely…but it’s true, nonetheless

This only applies to Alpha style drives (MC-1, R, MR, Alpha One, Alpha One Gen II).

In the mid 90s Merc changed the gears in the lower housing to reduce gear noise. The gear sets in the top box remained the same (and the main way the overall drive ratio is changed, mostly) and that's why you get that small ratio change. 1.5 became 1.47, 1.65 became 1.62, 1.84 became 1.81 and 1.98 became 1.94. The change (in the lower housing ) was from 17/28 to 13/21.

The 2:1 ratio is a 24:24 upper set and a (from memory, I think) 14:28 lower.

And yes, plenty enough 5 litre V8s were put out there with 1.5/1.47 drives.

Chris.....

 

[Rick Stephens]

Thanks for the info.
Okay after much digestion I see what your saying.
Is there any way to determine gear set in a gearcase without pulling it apart? Probably with a dial of some sort and beyond my ability....

And if I'm understanding properly, there should be no problem taking all of the guts out of a worn alpha one gen 2 2.00 ratio gearcase housing, races and shims included, and put them into a nicer alpha one gen 2 unknown ratio gearcase housing?
And I wouldn't run into any issues I'd just have to reshim or not reshim?
Thank again folks
Fully vaccinated I honestly just feel inebriated very strange and cloudy

Of note, it isn't very hard to pull the top cap off and mark/count teeth counts.

Also notice the gear change that Chris mentioned.

 

[QBhoy]

In the mid to 90s Merc changed the gears in the lower housing to reduce gear noise. The gear sets in the top box remained the same (and the main way the overall drive ratio is changed, mostly) and that's why you get that small ratio change. 1.5 became 1.47, 1.65 became 1.62, 1.84 became 1.81 and 1.98 became 1.94. The change (in the lower housing ) was from 17/28 to 13/21.

The 2:1 ratio is a 24:24 upper set and a (I think) 14:28 lower.

And yes, plenty enough 5 litre V8s were put out there with 1.5/1.47 drives.

Chris.....

Excellent info, as always Chris. Was hoping someone like yourself might come along and explain and elaborate a little better than I could.
Being fussy and at the risk of going back over my boat’s imperfections…I sometimes wonder if a step down and lower ratio, might be better suited to my boat and might just find me spot on and see my issues disappear! Anyway…a conversation for another time, perhaps.

 

[nola mike]

If it hasn't been mentioned already, you can just check the serial number of your drive and erase all doubt. But in general, on a 3.0, you'll want a general 2:1 ratio. 1.94., 1 98 isn't going to make a difference

 

[Mercperk]

Okay ya makes sense.
Sorry here's the abbreviated story; I'm repowering an old 63' Bertram 25 moppie mainly to replace the nasty old transom assemblies (no trim gauge sender, scary hinge pins not to mention the sketchy gimble rings) with original iron dukes(2.5l?) and preprealphas with 3.0l mercs, one new one used, used one came with a alpha one gen 2 2.00 ratio so to match that I'm piecing used lower unit components together and this whole 2.00 ratio matching uppers to lowers thing is confusing.
But if I understand correctly only the 1.62/2.00 ratio upper driveshaft housing mates to 2.00 ratio gearcase housing. Or y'all saying something different?

 

[nola mike]

Another thing to consider is the 'hunting' of gearsets. A nice even number like that with be a fully hunting gearset, meaning that certain teeth on one gear only ever mesh with limited numbers of teeth on the other gear.

Never understood a hunting gear set. In addition to the difficulties of reassembly, I'd think that you'd always want to spread the wear around to all the gears equally

 

[achris]

But if I understand correctly only the 1.62/2.00 ratio upper driveshaft housing mates to 2.00 ratio gearcase housing. Or y'all saying something different?

No, any upper will go on either lower (13:21 or 14:28)... But Merc only put the 24:24 upper (overall ratio 2:1) and the 20:24 upper (overall ratio 2.4:1) on the 14:28 lower...

Chris...

 

[Mercperk]

Not sure if you can get a clear enough image but what do y'all think about where the H2O pump plate sits. Too pitted or manageable?

 

[nola mike]

Okay ya makes sense.
Sorry here's the abbreviated story; I'm repowering an old 63' Bertram 25 moppie mainly to replace the nasty old transom assemblies (no trim gauge sender, scary hinge pins not to mention the sketchy gimble rings) with original iron dukes(2.5l?) and preprealphas with 3.0l mercs, one new one used, used one came with a alpha one gen 2 2.00 ratio so to match that I'm piecing used lower unit components together and this whole 2.00 ratio matching uppers to lowers thing is confusing.
But if I understand correctly only the 1.62/2.00 ratio upper driveshaft housing mates to 2.00 ratio gearcase housing. Or y'all saying something different?

Different... Do you have twins? If so, one should be counter rotating, which is done in the gear housing. Any of the uppers will mate with the lowers, with potentially a small difference in overall drive ratio. Normally this isn't something you'd notice, but if you have twins, a small difference may cause some drivability issues. If it was me, I'd keep the ratio exact between the two drives. (Btw, if you refer these engines as "iron dukes" or the drives as "pre-alphas", you're going to get somebody's panties in a bunch. Not naming names...)

 

[Mercperk]

I'm messed up in the head still....
So I have a 2.00r 24/24 upper and any gearcase will go on that?

 

[Mercperk]

Twins yes counter rotation gearcase for port yes

 

[Mercperk]

So that picture is the used gearcase unit for the starboard came with used motor. I have random alpha one gen 2 gearcase that's in newer condition and was trying to see if I could use it

 

[Mercperk]

But I don't know exactly the gearing in the newer random gearcase