can i convert a 25" shaft to a 20" Shaft?

[pflcjl]

I have a 115 optimax 25 inch and I would like to shorten to a 20 inch...Is this possible without a lot of work or is it not worth the effort....Can I do it with the existing shaft? Thanks...

 

[Chris1956]

Re: can i convert a 25" shaft to a 20" Shaft?

If the motor has a 5" spacer bolted to the midsection, you may unbolt it and change the driveshaft. The water tubes should have extensions that come off, and you will need to change the studs on the LU and midsection.

if no spacer, you need to change the midsection and the driveshaft.

Can you mount a jackplate on the hull and lift the current motor up 5"?

 

[pflcjl]

Re: can i convert a 25" shaft to a 20" Shaft?

thanks for the info....I rather stay away from a 5" jackplate....But it sounds like it is doable...correct

 

[Chris1956]

Re: can i convert a 25" shaft to a 20" Shaft?

Lifting the motor on a jackplate is possible. You will need to see if you can find a jackplate that llifts 5" and mount it flush with the top of the transom.

Alternatively, if you have a OB junkyard around, you might find a gearcase from a 20" motor and a replacement midsection. Maybe you could work a trade.

 

[pflcjl]

Re: can i convert a 25" shaft to a 20" Shaft?

It is a brand new motor....so I would not like to go to the salvage yard.....Is there a way just to remove the spacer on the lower unit and re-attach the shaft and whatever else needs to be connected? Thanks....

 

[Chris1956]

Re: can i convert a 25" shaft to a 20" Shaft?

The driveshaft, shiftshaft and studs on the lu and midsection are unique to the extralong shaft. These need to be changed out to shorten the length.

 

[kabcpapc]

Re: can i convert a 25" shaft to a 20" Shaft?

You can buy a CMC ML-65 adjustable jack plate for $240.00 or less. At a place called The Sports Center in Perry, GA ( like a Bass Pro store but locally owned) they have the ML-65 for $219.99. This probably will be cheaper than the other way.

http://www.thesportscenterstore.com/proddetail.php?prod=241206

 

[pflcjl]

Re: can i convert a 25" shaft to a 20" Shaft?

Thank you very much for the info.....Good stuff...Now you peaked my interest in a Jackplate....Can you tell me more.....Like how does it bolt to the transom? Can I use the same holes that are in the transom where my 90HP mercury is attached or do I have to drill more holes and plug up the existing ones.....Are there any drawbacks to the Jack plate....will it affect the integrity of the transom...can it handle ocean wave pounding? The application is a Boston Whaler Dauntless 16....Thanks again

 

[Chris1956]

Re: can i convert a 25" shaft to a 20" Shaft?

The Jackplate shoukd use the same holes as the motor, so it should bolt to the transom. On a 16 footer, 150HP is pretty large. I assume the boat is rated for it?

A jackplate gives a setback to the motor. Make sure the steering and control cables are long enough. The center of balance of the boat will be further back, as well. Any jackplate will be strong enough to take the same pounding the motor will take, in the ocean or anywhere. It will be best if the jackplate has 6" or so of lift. You can raise the motor more, after you add in the setback factor.