[phillycincykid]

good day all,

Ive had the rare opportunity to store my boat inside a heated space this year, in hopes to finally finish this project i started 4 years ago.
I found a few lower units to replace mine, and the price i got them for and the condition they are in if they dont work on my boat i can sell them for double my money, anyway, how do i know what the gear ratio is on the lower unit. there are few markings on them. I know the one i bought is definitely a alpha one, gen one but that's it. is there a tell tale sign of the gears in these things?

cant wait to boat again.

[ShabahZ280]

There's a couple ways to tell.

Usually, the gear ratio is stamped on the decal with the serial number on the outside of the housing. However if it's seen any significant amount of water, chances are this will be hard to read, or gone.

You can also get the letter code on the u-joint yoke. Although I don't remember the letters and what ratios they mean off the top of my head, so check out the link below.

You can also count the teeth on the upper gear.

Here's a quick link that may help you identify what you've got.
Mercruiser Stern Drive

[phillycincykid]

ok. ill have to look thru the ones i got. they are not in too bad of shape, so i should be able to find something.

[phillycincykid]

if the out drive i have on my boat is a 1.50 - 1 , how do i know the lower unit will work, the upper unit on my boat is staying, im just swapping the lower unit mainly for the case. does the lower unit matter as long as its a alpha one b/t 83 and 90'? my existing lower works just fine, but the cavitation plate is broken beyond repair.

[phillycincykid]

for everyone's knowledge, i spoke to someone from sierra today, i was not aware of this , but if you are just replacing the lower unit on a r/mr/alpha one, all the lower units are universal b/t 83 and 90. hopefully the guy from sierra knew what he was talking about.