Lower Unit Interchange

[DixieBoatN]

I am looking to swap out the lower unit on my 1985 V150 XR2 due to it having a stripped reverse gear and probably bad clutch dogs on the reverse side. I have not disassembled it yet to find out, but depending on whether there is a drive shaft nut or not, I can not buy just the reverse gear. I have to buy the complete "forward gear assembly." Given this, I am thinking it best and easiest to just replace the lower unit with a good used one.

The question I have is how interchangeable are these things? I found a great deal on one that came off of a mid 90's 225, but the casing is a different part number from mine, so I am not sure if it will interchange or not. I know that the bullets (gear housing) on the XR2 was smaller diameter than a standard V150, but I am thinking that it is worth it to replace mine with the larger diameter unit for strength purposes. Will my prop swap over? Can I bolt up most lower units off of V motors as long as the shaft length is the same (20")? Is the spline count on the drive shaft and shift shaft the same through out the years?

Any thoughts or input is appreciated!

 

[Faztbullet]

Re: Lower Unit Interchange

The 225 will bolt up if its was off a 2.5 liter engine. The XR2 has the same housing as the 150/175/200/225 the XR4 was the smaller 1.78 ratio unit. All the XR2 & 150hp was a 2.1 ratio so if you change you may get a 1.87 ratio which wont hurt you but may have to change props. Yes you prop will work and the 2.0/2.4/2.5 lower from 1986-2006 wll bolt up the only difference is ratios

 

[DixieBoatN]

Re: Lower Unit Interchange

Is there a way I can tell what the ratio is without having the unit in hand? If I search mercruiserparts.com I don't find ratios listed for the parts/gears.

Also, you are saying that all standard (non XR4) housings are the 2.1 ratio just like my XR2? This means that as long as I do not buy a lower unit that came off of an XR4, I should be getting the same gear ratio?

Thanks for the help!

 

[Faztbullet]

Re: Lower Unit Interchange

If its off a 150 Merc/Mariner it is a 2.1 ratio unless its of a XR4 or Mag II which are the small diameter 1.78 units. If its a175/200/225 it will be likely a 1.87 ratio. Here is a list of Mercury ratios.
Model Dis. HP RPM Ratio
Mercury XR2 2.0L 150 5500-6000 2.00/1
Mercury XR4 2.4L 150 5300-5800 1.78/1
Mercury XR6 2.5L 150 5000-5600 1.87/1
Mercury XRi 200 5200-5900 1.87/1
Mercury 2.0L 150 5000-5600 2.00/1
Mercury 2.5L EFI 150/175 5000-5600 1.87/1
Mercury ('99) 2.5L 200 5000-5600 1.87/1
Mercury 2.5L EFI 200 5000-5800 1.87/1
Mercury 3.0L 225 5000-5500 1.75/1
Mercury 3.0L EFI 225 5000-5800 1.75/1
Mercury XB 3.0L EFI 250 5800-6100 (6250) 1.75/1
Mercury Optimax 2.5L 150 5000-5600 1.87/1
Mercury Optimax 3.0L 200/225 5000-5750 1.75/1

 

[DixieBoatN]

Re: Lower Unit Interchange

Thanks a ton for the info!