1957 Johnson 35hp rebuild for higher HP

[Alex Novo]

Its happens that I ended with a working Javelin and a Seahorse, also a lock up seahorse for experiments and the question its:
Can I machine the cylinders and install new oversize pistons for higher power or I will fail because the engine cant take it?
Does the gain in HP justify the work and expenses?
Would the lower unit hold to increase of HP?
Any changes to reach higher RPM in a safe manner.?
Rejet Carbs?

Following this forum advises I had modify the fuel delivery, changed ignition points for Atom electronic ignition, use 24:1 instead of 50:1 mix ratio and results are so far positive before water test.

Failure its not a option when we compound our knowledge.

Thanks in advance

 

[racerone]

Gears and bearings were bigger / stronger on that motor than what you would find on a 2003 model 50 HP.

 

[Faztbullet]

Can I machine the cylinders and install new oversize pistons for higher power or I will fail because the engine cant take it?​

Boring does not add additional HP!!! Bored to max spec it might add 1-2 HP...HP is gained thru intake increases and porting.

 

[Alex Novo]

Good point. Next engine that Johnson built on 1958 was the 50hp , as expected parts don match at all . Will take motor a part in order to get familiar with it.

 

[Alex Novo]

Bore cylinder out of picture thanks. Will move to intake and port. Machine shop will know about how much to cut the intake or there its calculations? . Not a fan of try and error.

 

[racerone]

The carburetor has an adjustable low and high speed jet.-----So why / how would you " rejet the carbs " as you stated in post #1 ?-------Good luck with your project.

 

[Alex Novo]

Racer. Small miscommunication. When I stated JETS I was referring to carb nozzle. Modify the nozzle will change the fuel/air ratio for better or worse. Fine tuning can be done with the oem needles.

 

[F_R]

35hp was 3-1/16" bore. 40hp was 3-3/16" bore. Want an easy way to make it a 40? Slap a 1961-63 Gale Buccaneer or Ward's Sea King 40hp powerhead on it. I'll leave it up to you to figure out all the little details, such as hood mounts, etc.

 

[54bobby]

Mod EDIT: not permitted

 

[racerone]

Saw a 1958 35 HP on a nice little speed boat once.------Closer inspection revealed that it was about a 1984 model 60 HP with an old 35 HP cowling fitted to it.

 

[jbcurt00]

Mod EDIT: not permitted

54bobby Solicitation is prohibited

 

[Alex Novo]

A very good option to change the complete power head. Since I work on a golf cart shop a dc motor was another option but hp and rpms are way to low.

 

[jimmbo]

Saw a 1958 35 HP on a nice little speed boat once.------Closer inspection revealed that it was about a 1984 model 60 HP with an old 35 HP cowling fitted to it.

I would have liked to see how he got the 35 Cowl to fit and secured to the 60 pan. It probably was a bit of Ingenuity

 

[racerone]

Yes the party that did the job spent lots of time measuring / fitting.----Result was obviously worth it to that individual and no one else.

 

[Alex Novo]

Duct tape, self tappers, wood and aluminum, JB weld and lots lots of time.