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Questions Converting a 25 inch shaft over to a 20 inch shaft

K

Kongfish

New member
I have a 2011 Mercury 90hp Four Stroke EFI outboard with the X-Long 25 inch shaft lower unit that I need to Convert to a 20 inch short shaft lower unit. I have two questions about converting the lower unit over to being a 20 inch short shaft.
A.) would I be much better off replacing the entire lower unit with a intact whole lower unit with a 20 inch shaft lower unit? or
B.) Would buying all the parts needed to do the conversion job be just as reliable way to get the 20 inch shaft lower unit ?
Can anyone provide me with a link or a download of the correct shop manual needed to swap out a 25 inch shaft for a 20 inch shaft? I need to see if this is a job I feel like I can finish correctly?

Can you provide me with a complete parts list I will need to do the conversion correctly?
SERIAL #. 1B853167 of my motor.
 
????-------------------If the motor does not have a removable 5" spacer on the exhaust housing it will not be worth persuing this project !!
 
Agree - new lower unit is what? 2 grand, another 900 bucks for the housing, plus a few gaskets etc.

A good jack plate (adjustable) can be had for a couple hundred bucks - a transom elevator is under 100 bucks.

A brand new motor (90 EFI 4S) can be had for about 8K, you don't want to spend almost half of that turning your XL into a Long shaft.

But this may simply have the spacer. That would still leave you with a $700 driveshaft to replace and $75 shift shaft and about $70 for a new water tube. Unlike some OMC models, it doesn't look like Merc used a stub shaft (drive) to increase a long drive shaft to extra long - was a totally different part.

That would mean, however, that you would have to tear down the lower unit to remove the existing drive shaft - while it can be done at home, a couple of special tools is often needed. In particular, the pinion gear must be correctly torqued back onto the new driveshaft or it can cause issues. If you have a shop do that for you the cost of the retrofit goes up considerably.
 
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It should have a 5" spacer as all the 4 stroke 25" motors I have seen have them. If so all you need to do is have driveshaft and shift shaft changed,shorter studs to hold gearcase on. No need for water tube replacement and driveshaft is $450 and shift shaft $60 here on this site.
 
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