55hp johnson

[madcat]

I have a 55hp short shaft does a 70hp powerhead fit straight on or need adapter plate? And if it does fit is the drive shaft the same spline?

[oledawg]

You will need the 70 hp adapter plate to accommodate the exhaust outlet and tuner requirements of the 49.7 or 56
.1 cid motors. The splines are different as well. The 49.7 & 56.1 cid early models have a 4 tooth spline rather than a multiple tooth spline as on the 2 cyl. 45 cid, 50,55, & 60 hp models.

[madcat]

Thanks for that.

[25XS]

Just to be clear, madcat, do you have a two cylinder or three cylinder Johnson shortshaft engine your are asking about? (they made both)

[ACAMS]

If it is a 3 cyl then I can answer lots of your questions.

[madcat]

I'm sorry it's a 2cyl. I wanted to use the short mid and bolt 3cyl power head on for my thundercat. The 2cyl will be too slow compared to the 50 tohatsu..

[ACAMS]

Way too much trouble .... the exhaust adapter has a different bolt pattern and the drive shaft is smaller with a different spline.

Put the carbs off the 70 on it with some 75 Stinger jets and install some boyesen reeds and it will outrun the 50 tohatsu.

[ACAMS]

What year 55 2 cyl?

I have never seen one

[madcat]

I've got 2 55hp 2cyl motors. 1 has been mocked up with lightweight sst cowl ,nosecone box . I haven't checked comp but it takes a lot of battery power to crank it. I'll get some carbs reeds and put a tiller on it and see how it goes..I'm in Australia so maybe only come out here the 55 2 cyl? Thanks for your help

[25XS]

I'm sorry it's a 2cyl. I wanted to use the short mid and bolt 3cyl power head on for my thundercat. The 2cyl will be too slow compared to the 50 tohatsu..

Ok, I hate to keep stirring this pot, but there was BOTH a 2-cylinder, 55hp small gearcase fishing engine AND a Commercial Johnson 2-cylinder (several years offered) that had a 3-cylinder gearcase with low ratio for workboats. Just post your engine model number at this point so we can be certain on what combination of parts you are starting with. There were short & longshaft 2-cylinder Johnson's with the 2-cylinder gearcase and with the 3-cylinder (Commercial) gearcase. I have a 1990 45hp Johnson Commercial engine, too, and plan to at least install the 2-cylinder gearcase on it for increased speed.

[madcat]

Yep no worries I'll get pics of numbers tonight.. Sorry about that

[MTECHMARINE]

Gear ratio of the small 40-60HP gearcase is way too low to adapt to the 3 cylinder, even if you did a 2 piece D/S setup. In the day we ran the same propeller for SD as SE, 2 vastly different (45cid 55 hp twin VS Stinger 49CID 75HP) motors