Alpha One Gear Ratio

[Incorrigible]

Mercruiser Alpha One Lower Unit.

I found the listing for how many teeth each gear is supposed to have for identifying the gear ratio.

Based on the data I found, the 1.5:1 should have a DRIVE gear with 20 teeth and a DRIVEN gear with 22 teeth.

My questions are as follow:

Is the DRIVE gear the one that sits on the HORIZONTAL shaft, or the shaft coming through the transom from the engine?

If so, that means that the DRIVEN gear is on the VERTICAL shaft in the lower unit?

Assuming that is corrrect:

Is it possible to put them in backwards?

Thanks!!!!

 

[oldjeep]

Re: Alpha One Gear Ratio

The gears are in the upper unit not the lower.
The drive gear is the one attached to the horizontal shaft coming from the motor

 

[Don S]

Re: Alpha One Gear Ratio

http://forums.iboats.com/attachment.php?attachmentid=154828&stc=1&d=1340728596











.

 

[Incorrigible]

Re: Alpha One Gear Ratio

My bad, I ALWAYS refer to the whole sterndrive as the "lower unit"...

Thank you for the diagram. That explains exactly what I'm asking.

Now: Are the Drive gear and Driven gear interchangeable?

I'm pretty sure I have the 22 tooth gear in the DRIVE position, and not the Driven position....

 

[Don S]

Re: Alpha One Gear Ratio

Now: Are the Drive gear and Driven gear interchangeable?

No, and they come as a matched set. Don't even think about trying to replace just a drive gear or just the driven. They neither one would last long.

 

[Incorrigible]

Re: Alpha One Gear Ratio

The reason I'm asking? I BELIEVE I counted correctly, and that I have a 22 tooth DRIVE gear and a 20 tooth DRIVEN gear. I'm certainly going to recheck this, but I'm almost positive that's what I found.

Looking at the diagram above (and the other five sources that sent me the identical information) there is no such combination....

...leaving me VERY confused.

 

[Incorrigible]

Re: Alpha One Gear Ratio

Sorry: Forgot to add: I'm not looking to do anything other than verify and if need be correct the lower unit gearing to the 1.5:1 ratio. Thanks for the information here. This is helping immensely...

 

[Turn-n-Burn]

Re: Alpha One Gear Ratio

the alpha 1 lower unit has a 1.62 ratio......the upper unit is where they change the gear sets to get the proper ratio for the engine sizes......you have the gearing correct in the upper if you have the 22t gear on the engine side shaft.

lower unit gear ratio 1.62 divided by the upper gear ratio 1.1 = 1.47 ratio

 

[Incorrigible]

Re: Alpha One Gear Ratio

Turn-n-Burn:

Thought you were a nut job, but you pointed me to an answer:

I spent some time with an engineer doing some math on gear ratios:

The information I received on the Drive gear teeth count versus the Driven gear teeth count was TRANSPOSED in my case (and in a few others) From the parts description here on iBoats if you're looking for gears:

Mercruiser Upper Unit Gear Sets



Upper Unit Gear Set for Mercruiser 43-18410A2 43-18411A2, GLM 11210 - Sierra
Sale Price: $333.99
Save: $85.01 (20% Off $419.00)

For:
Most Mercruiser V-8 Drives and Gen II(S/N OK999999 & Below) with 1.5:1 Gear Ratio(Drive Gear = 22 teeth, Driven Gear = 20 teeth). Also fits Mercruiser stern drive models: 225 (S/N 3856268 - 4200499), 260 (S/N 4898730 - 6225576), 898/228 (S/N 4782330 - 6225576), 888 (S/N 3106717 & UP), V8/MR/Alpha One (S/N 6225577 & UP).

If you do the math from the upper unit gear ratio and the lower unit gear ratio, having 22 drive teeth and 20 driven teeth (not the other way around) the math works out perfect.

Your answer was spot on!!! The charts (the NUMBER of them I received) were wrong. Hat's off to you, "Turn-n-Burn"

 

[Incorrigible]

Re: Alpha One Gear Ratio

No, and they come as a matched set. Don't even think about trying to replace just a drive gear or just the driven. They neither one would last long.

View attachment 154830

Don: The chart you sent is erroneous. The 1.50:1 and the 1.47:1 have a DRIVE 22 and Driven 20

 

[Don S]

Re: Alpha One Gear Ratio

Well, I guess the manual has them wrong.
PS: You do have the special tools for setting gear heights and rolling torques don't you? You can't put in new gears with old shims and expect them to come out with proper rolling torque and gear height.

 

[ktbarrentine]

Re: Alpha One Gear Ratio

My bad, I ALWAYS refer to the whole sterndrive as the "lower unit"...

Excellent discussion on gear ratios, and thanks, Don, for a nice cross-section view of my drive. I will use this in future discussions, I'm sure.

Just curious, Incorrigible....if you refer to the whole sterndrive as the "lower unit", what is your "upper unit"?

 

[abrx7]

Re: Alpha One Gear Ratio

The upper unit houses the drive gear and drivin gear. The lower part houses the water pump and forward and reverse gear. Look at the drive and you will see bolts holding the 2 halves together. The unit as a whole is called a stern-drive.

 

[ktbarrentine]

Re: Alpha One Gear Ratio

The upper unit houses the drive gear and drivin gear. The lower part houses the water pump and forward and reverse gear. Look at the drive and you will see bolts holding the 2 halves together. The unit as a whole is called a stern-drive.

great answer....but that wasnt the question...

 

[Incorrigible]

Re: Alpha One Gear Ratio

ktbarrentine: Sorry, I should have stated that as "I ERRONEOUSLY call the sterndrive the lower unit" - abrx7 seems to have it the way I understand it to be correctly:

Don: Nope. Taking apart the lower unit is something I'm not ready to tackle. Your documents and attachments, I must say, provided me more information to help better understand and more accurately troubleshoot the true problem I'm chasing. Greatly appreciate the effort and have benefitted from it incredibly. As well, the attachment you sent that has the count of gear teeth incorrect? I received three from multiple sources and they all had at least one error.

As to gear ratios:

We worked through all of them. There are two sets of gears in the "sterndrive" (I'm learning) - there is the set in the upper unit and the lower unit. The product of the TWO of them develops your drive ratio. Anyone wishing to continue that conversation, or looking for more information, I'd be happy to share our work....

 

[Don S]

Re: Alpha One Gear Ratio

Might want to look at this thread on the Gen II outdrives and the gear ratios, and how to figure the ratio by tooth count.

http://forums.iboats.com/showthread.php?t=471939&p=3196951#post3196951

 

[ktbarrentine]

Re: Alpha One Gear Ratio

ktbarrentine: Sorry, I should have stated that as "I ERRONEOUSLY call the sterndrive the lower unit" - abrx7 seems to have it the way I understand it to be correctly.

I sure hope you were smiling while writing.... I find it hard sometimes to try and inject some humor into the thread and not have it come out like (unintentional) sarchasm.... I'll have to work on that! Anyway, this has been a good thread and I know I learned a thing or two about gear ratios! Thanks!

 

[achris]

Re: Alpha One Gear Ratio

Ah, but we haven't discussed the OTHER ratio in the lower...

Yes, Merc did produce another set of gears for the lower, (14/28) and that changed the overall ratio to something completely different when using the same upper.... It was only ever used with 20/24 and 24/24 uppers, to give overall ratios of 2.4:1 and 2.0:1... But we'll leave that for another day...

Oh, and one more thing (just to throw another cat in among the pigeons)... Around 1996/97 (I think) Merc changed the tooth count in the lower to 'reduce gear noise' (from 17/28 to 13/21). This reduced the overall ratio by about 2%... And that's why you see some listed as, for example, 1.50:1 and other as 1.47:1.... (with the same upper)...

The full list of that slight change is...

1.32:1 -> 1.29:1
1.50:1 -> 1.47:1
1.65:1 -> 1.62:1
1.84:1 -> 1.81:1
1.98:1 -> 1.94:1

Have fun...

Chris.........

 

[Don S]

Re: Alpha One Gear Ratio

Ah, but we haven't discussed the OTHER ratio in the lower...
.

Yes we did, look at my link in reply #16 And also note that's in the Gen II drives only, not the Alpha or earlier.

 

[achris]

Re: Alpha One Gear Ratio

Yes we did, look at my link in reply #16 And also note that's in the Gen II drives only, not the Alpha or earlier.

Yeah, ok... I only looked at the post that link pointed at... Didn't scroll up to the previous posts... My bad... sorry (please don't kill me... )

...And also note that's in the Gen II drives only, not the Alpha or earlier.

??? really???? Have a look at page 3A-3 and 3A-5 of service manual #6 (R, MR, Alpha One drive service manual)

Chris.....