48 years...

[stan2076]

Well, after 48 years (9 years in my possession) my '75 OMC120 stringer gave up the ghost. I'm sad that she didn't make 50, but not broken up about it, I know they get a lot of bad press but for me it was a good setup that was easy to wrench on and was actually very reliable. Suddenly lost 50% power with an audible sharp rapping coming from the engine. Not sure what it is but I'm not going to go down the path of repair.

Picked up a 2017 Honda 115 outboard. Plan is to engineer a structural transom mount that will bolt to the existing stringer mounts applying force to the boat in essentially the same way as before.

I know the center of gravity of the engine mass will be moving backwards but with the reduced weight of the new engine and moving the fuel tank to the front of the pontoon and some other weight management steps I'm cautiously optimistic that it will maintain the same plane as before.

 

[racerone]

Those 4 cylinder units 120 / 140 HP are very robust.----Used for many years by Mercury / Volvo / OMC.------A good used one would not be hard to find.

 

[stan2076]

Those 4 cylinder units 120 / 140 HP are very robust.----Used for many years by Mercury / Volvo / OMC.------A good used one would not be hard to find.

I agree, great motors, but with the outdrive in the same vintage I'm ready to move on. I have another outdrive with a failed electric shift, will package it all for any remaining stringer die hard.

 

[Scott06]

@Scott Danforth might have some thoughts.

Would have the transom plate replaced and made the thickness of the transom mount on the new outboard. have that time into C channel or boxed tubing on sides of motor bath tub to spread the load so be no issue.

 

[racerone]

Electric shift failure is usually a broken clutch spring , broken wire or loss of 12 volts on a wire.----Easy to inspect

 

[Scott Danforth]

If you want to stick with stringers, look at the 81-84 with a 3.0

However the idea of modifying the transom and going with modern power will be less headaches..... I would look at a center log with a motor transom.

Then again, Doc's Harleydavidson https://docshd.com/ has/had a V-twin powered stringer on an old pontoon boat for years. the motor sits on top the drive, a chain goes down to where the ball gear on the upper sat.

 

[Redrig]

I converted my electric stringer to a mechanical a few years ago and it's been working out well .

good luck with your project . It will be interesting to see the outboard get on there . I'll be following along

 

[airshot]

Cool looking project, please keep us updated and by all means lots of pictures !!

 

[stan2076]

When I bought the boat the fuel tank was on the front of the pontoon in a reversible seat base. I fabricated a frame off the back of the boat and mounted it there to get it out of the way.

It will interfere with the outboard so it has to go.


Funny how taking something apart goes so much faster than putting it together.

Built a heavy duty outboard stand from some scrap stands from my work's metal dumpster. These were paper holders for packout stations where they used brown paper for void fill like foam peanuts. They switched to plastic pillow packs and tossed these stands.




Drove to Michigan and picked up the motor


Cozied up to the boat



It's about 100 pounds lighter than the old OMC120 setup, but center of gravity is moving back. Any predictions on how the boat might sit in the water? This was the waterline with the old setup.
(My hydraulic boat lift burst a hose so she sat in the water all summer)

 

[stan2076]

Also, any thoughts on transom angle? Seeing 12 to 14 degrees...

 

[stan2076]

Also, any thoughts on transom angle? Seeing 12 to 14 degrees...

Came across this in the installation manual of the BF115. Honda shows 12 degrees. Any reason to do something different?

 

[Redrig]

Sorry can't help with trim . Iver owned an outboard .

But wheres the fuel tank going ? Based on the weight shift of the OMC vs outboard. moving it forward could help with weight distribution and how she sits in the water

And great job

 

[stan2076]

Sorry can't help with trim . Iver owned an outboard .

But wheres the fuel tank going ? Based on the weight shift of the OMC vs outboard. moving it forward could help with weight distribution and how she sits in the water

And great job

Thanks, a long way to go

The fuel tank will probably go back to the front, I preserved the fuel line going to the back of the boat so it should be relatively easy to hook up.

 

[stan2076]

Measuring many times before I make any cuts
Starting from the current waterline and using the guidance from the installation manual. I may need to add a couple inches to the bottom of the old engine bay to maintain the 1 inch distance between the cavitation plate level and the hull bottom. It's about 3 inches instead of 1 inch.

 

[stan2076]

Marked out 12 degrees...

 

[stan2076]

Top of the transom clamped in position after lots of measuring, positioning, measuring, etc...


Side cuts made

 

[stan2076]

Might have sprung a leak...

 

[stan2076]

Making progress, top of the transom tacked in place sizing up the new back plate.

 

[stan2076]

Got the Healtech Honda software and connected to the new Honda. Only 74 total hours, I'm stoked it's practically new.
Anyone know what Overrun Running Time means?

 

[stan2076]

Got my fuel tank, the old one was steel, 12 gallon, this one is a 14, should be more than enough for my needs. A bit concerned about throttle/shift cable clearance but should be ok I think.