25xd to 25xs Conversion

[Jho928]

Hi,First I'd like to say this is a great site and it really has sparked an interest for me to get involved .I have a Merc 25xd on a homebuilt 12' Runabout I wish to convert to a 25xs. The boat is heavy but once I get the motor done I will possibly build a racer .I have been doing some research on this and I believe it is possible .I have found the parts lists and sources on this site(great work to those responsible for this) but one could imagine I have questions.
1.The exhaust housing and adapter plates available from IAI will bolt to what gearcase ? Can I use any ABC gearcase or does it have to be a 25xs case or 25ss etc .
2.What gear ratio would be best for my situation? The boat is over 200lbs and I want to be sure the low end power is there to get it out of the hole.
Who can supply the gears ?
3.What is involved with fitting the drive shaft ? Do I use my 25xd driveshaft and modify it?
4.Will my 25xd powerhead bolt on to the adapter plate with out any mods ?
5.What could be and or should be done to the power head?
Hone ,new pistons ,rings,reeds,carb-fuel pump work,flywheel etc.

Thats about all I can think of for now I am sure I am missing alot .I hope to disscuss this with you all further .

Thanks for the much anticipated and appreciated help.
Jim

[jeff55v]

Conversion

Instead, how 'bout a 25xd to C conversion? Sell the 25xd, use the money toward a good 102 or 302 Yamato. Parts are readily available and probably a stronger C participation in your area. You'll likely spend more for a 25xs lower unit and tower than what an entire C motor costs.
Just my two cents. Whatever you do, have fun! And welcome to the sport!

[Jho928]

Thanks

Thanks for the sugestion I was thinking of doing something like that ,however the tinkerer in me wants to convert the 25xd.I guess if it came down to money no one would be into this . Jim

[swheeler]

Any Merc ABC or 25ss/25xs gear case should fit the driveshaft housing. You will need a driveshaft that will fit the gear case and match up to the crank shaft. The simpliest way to do this would be to get a 25xs gear case as that would have the correct driveshaft in it. You could also use a coupler in the driveshaft to match up the correct upper and lower ends or have a shaft made by welding the correct upper and lower together. I would use the 16/21 gear ratio.
The powerhead should go on the adapter with no problem. You will need to replace the bolts that hold the powerhead to the fishing driveshaft housing and install studs in the powerhead.
I appreciate the project but would warn that if you are thinking about racing at some point you might check to see what classes are active in your area and where this engine might fit in before you spend alot of money.