1955 25 horse Johnson

[55Crestliner]

I've been wanting a bit bigger motor than the 18 horse, so I finally got one. A friend of my dad's GAVE me a 25 horse 1955. Last year of the green, first year of the "fin tail" Johnsons. <br />Motor seems to be in real good shape, I'm anxious to do a compression check, and see if it'll run.<br />This motor still has a green prop, hardly any paint worn away, and NO chips - amazing.<br />So far, the worst part of the motor is the few spots of corrosion, it's bubbling up the paint in a few places. Otherwise, the decals and other paint is almost perfect.<br /><br />So, here's the question. <br />Has anyone had experience with going from a '50's 18 to a '50's 25? Is the approximately 40 pounds extra weight worth it? I'm assuming the accelleration will be better, especially when loaded. This is going on a 12 foot aluminum, rated for 30hp, and the boat is relatively light.<br />(see my signature)<br /><br />I'm very curious to see if it's a pig for gas, it might just be better at mid-range, being it can be at a lower RPM - right?

 

[WillyBWright]

Re: 1955 25 horse Johnson

The pistons are quite a bit bigger. In later carnations, they became 30 and 35Hp. You'll notice a lot more power, but they're a SOB to pull start!

 

[55Crestliner]

Re: 1955 25 horse Johnson

I bet - I'd love to get a starter setup for it. I find it odd that it does not have a toothed flywheel like the new ('57) 18 horse. <br /><br />Well, I'll have to ask - what did they do to the 25 to make it a 30 or 35? Just the carb or is it the usual crank/exhaust/carb etc that makes it "bigger"?

 

[Paul Moir]

Re: 1955 25 horse Johnson

30 I think was head. I'll look it up.<br />35 was bigger pistons. No you cannot fit them to your 25hp.<br /><br />The 25/28/30/33/35/40hp engines from the '50s-early 70s are all related, except the '69- 25hp.

 

[Chinewalker]

Re: 1955 25 horse Johnson

Yep, The biggest difference between the 25 and 30 (both 35.7 cubes) was the shape of the piston dome and cylinder head. The 25hp was a 5:1 compression ratio, while the 30hp was 6:1.<br /><br />The 25 is a solid lugger, and you'll notice quite a difference in low end kick. They didn't do too bad on high end, either. Make sure the engine is propped right for your light boat. There are a few Michigan 2-blades out there in the 14-16 inch pitch range that could help keep the Rs down if the motor does rev too much. I don't like to see those Big Twins spin much more than about 4600-4700 RPM. The stock 3-blade that came with your motor may not be enough prop.<br /><br />- Scott

 

[55Crestliner]

Re: 1955 25 horse Johnson

Originally posted by Chinewalker:<br />The stock 3-blade that came with your motor may not be enough prop.<br /><br />- Scott

I can't wait to see how it works out. I have a tach, I'll see what it's turning.<br /><br />Thanks for the info on the 25-30-35 issue. I, like most, just wanted to be sure it wasn't a simple "change the jet" thing. I won't be opening it up to change anything. <br /><br />btw, what is the stock prop? Is there such thing on this motor? Or would they prop it when purchased to the buyers needs?<br />I haven't found any numbers on it, but haven't had it off yet either.

 

[Paul Moir]

Re: 1955 25 horse Johnson

Back then I think they all put the numbers behind the thrust washer, and it'll be an OMC part number. But if it was used much in salt, the numbers will be gone due to galvanic action. The stock prop was 10-3/8 x 12-1/2, but who knows whats on there now. <br />The '60s 40hp props should fit your propshaft just fine, and 14" ones of those are pretty easy to find. But a 2 blade would be really cool.<br /><br />EDIT: Some of the older props had their diameter and pitch numbers on the back of the propeller between the hub bore and outer housing of the prop, way in there. I think they were doing that in the 50s.