Can I replace my 40hp with a 70hp motor?

[samviluong]

Help please
I have a 1963 16' Aroliner Debonaire with a 1964 Evinrude 40hp motor on it. The bottom end leaking a lot of gear oil and the starter went dead last year. My boat was rated for 40hp back when it was built, can I replace the motor with a 70hp Evinrude? The 40hp burn a lot of gas but never go faster the 20 mph. I don't want to race with anyone but sometime I need the power to get the boat back to shore when the water on the lake getting choppy. Any suggest would be appreciated.
The One

 

[tashasdaddy]

Re: Can I replace my 40hp with a 70hp motor?

there are legal problems with overpowering a boat. that said, if the transom is solid, to handle a 70, yes. we had a boat that size with a gale 60 hp, back in the dark ages.

 

[kenmyfam]

Re: Can I replace my 40hp with a 70hp motor?

Welcome to iboats.
If transom is good then should be O.K. as TD stated. Potential insurance issue if you are overpowered and have accident or claim.

 

[JB]

Re: Can I replace my 40hp with a 70hp motor?

Seventy HP is 175% of rated power. That is much too much overpower for safety.

It would be less expensive and a lot safer to simply get your 40HP in good shape.

 

[ovrrdrive]

Re: Can I replace my 40hp with a 70hp motor?

A 40 may have been just about the largest motor made back then so I'm sure the boats were rated differently. I say go for it and just be careful for the first few runs. More power may have some very strange adverse effects on a hull that's never been pushed that hard.

edit. Actually I just looked it up. a 100HP was the latest, greatest, and baddest motor out at the time. Still, hulls were rated differently because big motors were not widely available.

 

[JB]

Re: Can I replace my 40hp with a 70hp motor?

Read my lips, Sam.

Putting a modern 70HP outboard on a 45 year old boat rated for 40 (1964)HP is a VERY BAD idea.

If you are determined, and immortal, go ahead, but don't get the idea that the guys on iboats said it was okay.

 

[CATransplant]

Re: Can I replace my 40hp with a 70hp motor?

Help please
I have a 1963 16' Aroliner Debonaire with a 1964 Evinrude 40hp motor on it. The bottom end leaking a lot of gear oil and the starter went dead last year. My boat was rated for 40hp back when it was built, can I replace the motor with a 70hp Evinrude? The 40hp burn a lot of gas but never go faster the 20 mph. I don't want to race with anyone but sometime I need the power to get the boat back to shore when the water on the lake getting choppy. Any suggest would be appreciated.
The One

If it's the boat I'm thinking of, it's a fairly narrow aluminum boat for its length. If that 40 had been running properly, it should have pushed that boat almost 30mph. I wouldn't put a 79 on it, frankly. If it's rated for 40, that would be the limit. Try a good-running 40. I'll be you'll be very surprised.

Here's a Aroliner web site, they have all the specs, and your boat is definitely listed at 40hp max. They do have one 16' that's rated at 60hp, but it's 6' wide, six inches wider than your "open utility" boat. A 40 should make yours fly.


http://www.arolinerfanclub.com/index.html

 

[samviluong]

Re: Can I replace my 40hp with a 70hp motor?

Thanks guys
The motor that I want has been sold, so I guess I just have to fix my 40hp for now. 50hp or 60hp is what I really want for my boat, just have keep on looking for a good one.
Thanks again and happy boating
The One

 

[jay_merrill]

Re: Can I replace my 40hp with a 70hp motor?

There is no reason to put 60 hp on that boat. As others have said, if your 40hp is running right, it should go much more than 20 mph.

Your comment about it burning a lot of gas, combined with the low WOT speed, makes me think you have a low pitch prop on it. I recommend that you get a 2-stroke model Tiny Tach to see where you are in terms of RPM. My guess is that you are over-revving it and, hence, doing little more than beating the motor to death, making a lot of noise and burning up a bunch of fuel. If I am correct, you may want to consider moving up to a 14" pitch wheel. That is the maximum pitch that is available as a stock unit, but if it still isn't enough to get the WOT range where it should be, I believe that the aluminum, pin drive props can be "pitched up" about 1" to 1-1/2" by a prop shop. I'm going to guess though, that the 14" wheel will be about right.

If the rest of the motor is in reasonably good shape, you should be able to get the starter rebuilt for about a hundred bucks and the gearcase can be resealed relatively inexpensively too. Don't give up on this motor too soon!

 

[steelespike]

Re: Can I replace my 40hp with a 70hp motor?

Keep in mind a 70hp at 233lbs. is almost twice as heavy as the 40, it developes 75% more power and will use 75% more fuel at wot(wide open throttle)The 40 is rated for about 33 mph under ideal conditions.Properly tuned and setup it should do about 28 on your boat.

 

[samviluong]

Re: Can I replace my 40hp with a 70hp motor?

For weight wise, my old 40 is a huge motor and weight well over 200lbs. The 70 that I saw cant even weight close to my. Another thing is when I bough my boat 6 years ago it was a very plan boat so it ran max out at 25mph. After I added floor, 2 sleeper seats and a bench seat to the boat. It now weight over 300lbs more that is why I like to upgrade my motor to compensate for the extra weight on it.
Thanks for all the replies
The One

 

[jay_merrill]

Re: Can I replace my 40hp with a 70hp motor?

If your motor is a 1964 Johnson 40hp, it doesn't weigh over 200 pounds. In fact, it doesn't even weigh anything close to 200 pounds. The true weight of this motor is about 140 pounds.

I think you just want to go to a larger motor. If that is the case, so be it. We have offered you our opinions, and we seem to be in nearly unanimous agreement that what you have said you want to do, is a bad idea. The only thing that we can do now is to hope that you will proceed with caution.

 

[jay_merrill]

Re: Can I replace my 40hp with a 70hp motor?

Something that I forgot to post before - and I'll do so now in a new post in the hope that you see another response and read this.

Many people think that when an outboard is developing power but the transom fails, it will simply fall off of the back of the boat. It doesn't. Since the motor is creating thrust, it tries to enter the inside of the boat through the failed area, and the more power involved, the more violently it will do that.

Something to think about when contemplating putting an engine of nearly twice the rated horsepower, and nearly twice the weight of your old motor, on this boat.

 

[steelespike]

Re: Can I replace my 40hp with a 70hp motor?

For weight wise, my old 40 is a huge motor and weight well over 200lbs. The 70 that I saw cant even weight close to my. Another thing is when I bough my boat 6 years ago it was a very plan boat so it ran max out at 25mph. After I added floor, 2 sleeper seats and a bench seat to the boat. It now weight over 300lbs more that is why I like to upgrade my motor to compensate for the extra weight on it.
Thanks for all the replies
The One

64 40 hp is 137 lbs by the original manual,70 hp is 233 lbs.

 

[samviluong]

Re: Can I replace my 40hp with a 70hp motor?

I learned something valuable from you guys, the starter is off the motor and it will going to be rebuild. Found a guy going to reseal the bottom end for $100. Got a used 33lbs trolling motor for $100. I will be stuck with this motor for few more years and save some money for my future Pontiac Solstice when they come down to $10000 for a used one.
Happy Boating Everyone
The One

 

[steelespike]

Re: Can I replace my 40hp with a 70hp motor?

Now your on the right track.Be sure the throttle is opening all the way.
Optimize your setup, motor vertical height raise it a little at a time to just before venting becomes a problem,be sure clamps have a good grip and it pumps water. An inch increase in height could get 2 to 3mph.Carefully eliminate unecessary weight,distribute weight carefully and adjust trim.Get us your max rpm and speed, a prop change may improve your performance.