Can i run the same 200 hp merc with a 20" shaft instead of 25"?

ducerman · Sep 22, 2011

Can i run the same merc with a 20" shaft instead of a 25" on this boat?? The transome is 21" from top to bottom. The waterline goes up about 10" from bottom.

Texasmark · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Seems reasonable. Are you converting a 25 engine to 20, or just repowering with a 20"? The length of the transom vs the length of the engine seem to be a perfect match for best performance.

Mark

ducerman · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

I came across a 20" complete outboard for cheap.. The one in the pic on the yellow boat is blown up. Im not sure if the 25" lower housing is compatable with the motor on the 20" because the yellow boat motor is a 1978 (25") and the other is a 1988.(20"). I would like to run the new motor with my 25" but im not sure if there compatible concidering the age difference. Any info would be nice! Thanks for your reply!

Faztbullet · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Can i run the same merc with a 20" shaft instead of a 25" on this boat?

That does not look like a 25" motor as it does not have the 5" spacer between cavation plate and lower unit. A fairly easy way to tell is to drop lower unit and measure driveshaft. Measure from top of splines to top of lower unit, a 20" unit will measure 23" and a 25" will measure 28"

Sprky · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

The motor in the pic is a 20". The newer motor will have a different bolt pattern for the transom.

Do you get controls with the new motor?

Wiring will be somewhat different between the two.

ducerman · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Wow guys, thanks.. I didnt know it was a 20"! I guess thats why i leave it to the pro's! Well in that case i shouldnt have a problem with the new motor. The only difference is the remote hydrolic pump and built in trim. The housing on the new motor looks a little different but i believe has the same mounting holes. And yes, i will be getting the controls with the new motor thank god! As for the wiring, i was gonna replace it anyways so it wont be an issue. Thanks to everyone for the replies and if theres any problems i will run into feel free to let me know. Thanks again!

ducerman · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Here is the new motor mounted on a bass boat. And sorry, i re read this thread and sprky, you said the mounting holes will be different.. I assume it will be ok to redrill new holes as long as there not to close to the existing?? Sorry for the bad pic, but maybe this will helpView attachment 115184

Sprky · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Fill the old holes, drill new ones.

Assuming the new motor is solid, you will be much happier. You are going from a 122ci motor to a 142ci motor.... Lots more torque.

What length and model is your checkmate?

ducerman · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

View attachment 115196Its a 1979 checkmate enchanter 19'.

cr2k · Sep 22, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

As long as the cav plate is even with the bottom of the boat and your water pick up is in the water when on plane.

Faztbullet · Sep 23, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

As posted earlier, you will need to fill and seal old mounting holes as the 1988 is totally different. It will be best to run boat by a dealer and let him use a drilling fixture to mark holes for the newer engine. Also you will need the newer dual steering attachment kit for the 1988 if not installed as the 1978 will not fit. Also both motors are 142ci, the only 122ci 200hp engine made was the export racing Xr2 or in states it is called a SST120.

Sprky · Sep 23, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

I assumed because of the age it was a 2.0....... MY bad.

ducerman · Sep 23, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Thanks everyone for the great advise! It would of took me forever to find this info out on my own. I guess the next steps include drilling the new holes.. I made a fixture in my machine shop that sits flat on the transome with a uluminium template of the new mount. Should work fine. Next ill have to do what you said Faztbullet and buy the dual cable set up. Time to hit up ebay! Thanks again guys! thats why i leave this to the pro's..

Mi duckdown · Sep 23, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Just make sure when drilling, is that you have the correct angle to the transom.

mr 88 · Sep 23, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

Also oversize the holes so that the sealant,3m4200 will have something to adhere to and not all be squeezed out.It's also nice if you can counter sink or bevel the drill holes.This helps eliminate crazing/cracking/spider webbing[whatever you want to call it] of glass

Mi duckdown said:
Just make sure when drilling, is that you have the correct angle to the transom.

chum1 · Sep 25, 2011

Re: Can i run the same 200 hp merc with a 20" shaft instead of 25"?

The cheap foam paintbrushes have wooden handles that work perfect for dowels to plug and seal the holes in the transom.

Can i run the same 200 hp merc with a 20" shaft instead of 25"?

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