Mercury lower unit help... once again

[tsilvertooth]

Hey everyone. I have searched and looked and looked some more and I still can not lock down what lower unit I need for this motor.

It is a 1986 Mercury 150 XR2 Black Max. Serial Number is OA958389

When I search the parts it gives me the option for both the 20" and 25" shafts.

Prior person who tried to put a lower unit on it bought a 20" shaft and it was just about an inch short from measurements. The shaft was 20.5, and from the mounting surface by the water pump to the top of the shaft is 23".

When you measure from the inside of the splines off the flywheel to the mounting surface on the driveshaft housing, it is 24" making the short shaft just a hair to small, but seems like stepping up to a 25" would be to long.

I have tried to answer this question on my own, but after much research I can not figure out what I need.

Any help is appreciated.

 

[tsilvertooth]

Here's a picture of the motor

 

[racerone]

Inside the splines of the CRANKSHAFT is where you would measure.-----And the term long shaft 20" and extra long shaft 25" are NOT actual measurements of the driveshaft itself.-----It refers to the height of the transom of the boat.-----------So I think you need what is called a " long shaft " for that motor as pictured.----Measure the height of your transom to be sure !!!

 

[tsilvertooth]

I measured from inside the splines on the crank and that's where the 24" measurement was from. I ll measure the transom though and go from there, thanks!

I ve seen where some people are using the serial number to take out user error. Any ideas there?

Thanks again for the help, I did not know that about the shaft lengths.

 

[racerone]

Is this a " new to you " boat and motor ?------Best to do a compression test before spending the cash on a lower unit.

 

[tsilvertooth]

Good compression about 110 on all

 

[Faztbullet]

Need a standard 20" 2:1 ratio lower unit...