outdrive swap with 3.0l Merc

[jmoore73]

Forgive my ignorance regarding math and gear ratios. That being said... I have a 1990 merc 3.0 l with a Gen 1 out drive 1.94/1 ratio. I ran over a good size piece of lumber a couple weeks ago, and it looks like the vertical drive shaft sheared clean of the splines just below upper gear box.

Also, I holed the lower unit.

If I find a decent priced used out drive, ( Gen 1) does it matter what the gear ratio is? Will it fit?

I paid all of 2k for the boat, and after a $200 or so fixing hard ware and minor maintenance on engine ( runs great), its been a lot of fun . I don't really care about top speed I just want to get back on the water with some money left over to fill the cooler.

Any advice, counseling or wisdom is appreciated

Thanks

Joel

 

[boatguya1]

Re: outdrive swap with 3.0l Merc

http://www.sterndrive.cc/mm5/merchant.mvc?Screen=CTGY&Category_Code=MercruiserAlpha


Best bet

 

[Silly Seville]

Re: outdrive swap with 3.0l Merc

If I find a decent priced used out drive, ( Gen 1) does it matter what the gear ratio is? Will it fit?

Yes and yes.

All Alpha 1's have interchangeable upper/lower assemblies.

Your best solution is to find the same drive ratio (1.94) If not, you will be forced to up or down size your prop considerably in an attempt to bring the functional ratio back to "normal".

Example:

If you change gearing, say to a 1.50 (from V-8's) you will need to decrease prop pitch by at least two inches. Maybe four! So let's assume you are running a 14 1/4" x 19p currently. Figure on buying a 17 or even 15 pitch prop! This will effectively keep you in a usable RPM range, but it might not ever perform as it did before under the same circumstances. In a pinch, yes you can swap upper housings/gear ratios. Do you want to do it long term...ehh, the jury's out on that one.

 

[jmoore73]

Re: outdrive swap with 3.0l Merc

Example:

If you change gearing, say to a 1.50 (from V-8's) you will need to decrease prop pitch by at least two inches. Maybe four![/QUOTE]

So does that mean by dropping the pitch considerably it would reduce the load/resistance allowing the engine to compensate a little for the stouter gear ratio? Right now I have a 23 pitch S/S stiletto ( which didn't even get dinged when I hit that dang lumber) I know the local marina will let me trade that for 2 used aluminum ones with smaller pitch.

If I absolutely have to spit out the $1500-$1800 I guess I will, but I am a pretty frugal dude, and there are lots of used 1.50 and 1.81 ration drives locally on cragslist. Just no 1.94.

 

[Silly Seville]

Re: outdrive swap with 3.0l Merc

jmoore73...PM sent

 

[achris]

Re: outdrive swap with 3.0l Merc

Most lower units are the same. The only ones that have a different tooth count are the units with an overall ratio of either 2.4:1 or 2.0:1.

Find one from a 1.47, 1.62, 1.81 or 1.94 and the lower will be the same. Just find a good one that is pre-1990 and bolt it on...

If you are talking about the whole drive, you should really get one that has the right ratio (1.94:1)...

Chris....

 

[cr2k]

Re: outdrive swap with 3.0l Merc

If you just change the lower you are fine as the ratio is in the upper.

 

[jmoore73]

Re: outdrive swap with 3.0l Merc

If you just change the lower you are fine as the ratio is in the upper.

Ok. It appears the vertical drive shaft sheared, leaving the part with the splines in the upper gear box.

Any advice on trying to get that out?

I didn't see any metal in the gear oil when I drained it, and the when I turn the drive shaft (where the U-Joint it) by hand the upper gears turn freely and look to be in great shape.

from below, I can push something back up into the gear box, it moves up and down. Couple that with the fact that when I seaparated the lower unit the vertical shaft was completely smooth, and I know there should be splines there. So I think the part of the vertical shaft with the splines is still up there.

 

[jmoore73]

Re: outdrive swap with 3.0l Merc

I got the splines out of the upper gear box. Here are some photos. I should just be able to slap on a fresh lower unit, replace transom seals and such and go boating right?

What do you think?

 

[achris]

Re: outdrive swap with 3.0l Merc

yep...

 

[jmoore73]

Re: outdrive swap with 3.0l Merc

yep...

Awesome!

 

[TilliamWe]

Re: outdrive swap with 3.0l Merc

But now know that a brand new lower-unit-only from SEI is about $800. So don't spend close to that on a used with the wrong ratio.

 

[jmoore73]

Re: outdrive swap with 3.0l Merc

But now know that a brand new lower-unit-only from SEI is about $800. So don't spend close to that on a used with the wrong ratio.

Great advice! And as cheap as I am, believe me I will follow it!

 

[jmoore73]

Re: outdrive swap with 3.0l Merc

Great advice! And as cheap as I am, believe me I will follow it!

But now know that a brand new lower-unit-only from SEI is about $800. So don't spend close to that on a used with the wrong ratio.

But for clarification, if I do find a used Gen I lower unit only, they should be pretty much interchangeable regardless of what the gear ratio is in the upper unit correct?

 

[Bondo]

Re: outdrive swap with 3.0l Merc

But for clarification, if I do find a used Gen I lower unit only, they should be pretty much interchangeable regardless of what the gear ratio is in the upper unit correct?

Ayuh,... Once again,...... YES....