Transom adaptor from 15" to 20"?

[Christian68]

Hi,

I currently have a 1983 Evinrude 35 HP, short shaft, tiller (non electric start) on a 16' Lund.

I'm thinking about upgrading to a 1996 Mercury 40 HP, short shaft, tiller (this is the 4 cylinder) with Electric start, oil injection and power trim.

I'm happy with the older Evinrude but want the new features of the Mercury. Specifically the electric start. I'm told power trim will be really nice as well. And obviously not mixing oil will be nice.

I also read that the 4 cylinder Mercury should run a lot smoother.

My boat is rated for a 40 HP but I don't really expect any more power out of the 40 HP. If I do have more power then fantastic.

I think I've thought everything through and it seems like a no brainer upgrade.

Anything negative with the 1996 Mercury 40 HP 4 cylinder 2 stroke that I should be aware of?

Anything else I'm missing? Obviously I'll need to run a battery now but I have space for that. Now I could also run an electric trolling motor, charge phones, bilge pump, etc is all an advantage.

 

[racerone]

Some will argue.-----My approach would be to put electric start on the Evinrude 35 HP.

 

[JimS123]

I only had 2 oil injected engines in my lifetime. After the first I said never again. After the second I really mean it.

I truly like power trim, but I don't really need electric start, assuming that the engine starts well.

 

[jimmbo]

The 35 was rated at the Crank, the 40 is rated at the prop, and used to be a 50 horsepower at the Crank. The 35 has a displacement of about 38 cu in., while the 40 is 44 cu in. The 40 will be a much smoother engine, especially at low speeds, and is very easy to rope start as it has 4 smaller compression bumps, per rev, versus 2 bigger ones.
As for the Oil Injection, on the 40, that is probably the Auto Blend system, a Device spliced into the Fuel Line prior to the engine. If so, remove it from the line, throw it as far from the boat as you can, and mix TCW-3 @50:1.

 

[Christian68]

Thanks guys.

I think my bigger issue is the Merc has a 20" shaft and my transom is 15". So I may pass on the engine.

Or I'll look into an adapter plate to build up the transom. Not sure if I want to start drilling holes in my boat. My current Evinrude is clamp on and the Merc is bolt on.

 

[Christian68]

Hi, I have an older Lund 16' with 15" transom. Currently it has a clamp on Evinrude 35 short shaft.

I'm thinking about upgrading to a Mercury 40 bolt on with 20" long shaft.

What are my options to modify the transom to a 20"?

I'm thinking about making a bolt on riser that sandwiches the transom. And obliviously I'd have to drill some holes through my transom to bolt the adaptor and engine.

I would love to see pics of what people have done. Is this a terrible idea?

Thanks.

 

[Sea Rider]

Does the transom have the same width from where the motor sits to say middle or lower transom area ? Post pic if possible.

Happy Boating

 

[Christian68]

Does the transom have the same width from where the motor sits to say middle or lower transom area ? Post pic if possible.

Happy Boating

If your talking about the thickness I can't remember exactly. I'll look tonight and get some pics.

It's similar to this picture that I found on the internet. Example pic only.

 

[matt167]

You could use a 5 " jack plate

 

[Sea Rider]

If your talking about the thickness I can't remember exactly. I'll look tonight and get some pics. It's similar to this picture that I found on the internet. Example pic only.

If plan sitting the motor aligned fully vertical at transom level but 5" higher, this type of motor riser works very well, can bolt the lower holding plates at both sides (*) to install a L 20 shaft motor. Will need to be fabricated at a metal facility/workshop.



The overall cost should be much less than going per a traditional jack plate bolted at back transom which may offset way more the motor's weight backwards compared to a motor riser....

Happy Boating

 

[Christian68]

If plan sitting the motor aligned fully vertical at transom level but 5" higher, this type of motor riser works very well, can bolt the lower holding plates at both sides (*) to install a L 20 shaft motor. Will need to be fabricated at a metal facility/workshop.

View attachment 359616

The overall cost should be much less than going per a traditional jack plate bolted at back transom which may offset way more the motor's weight backwards compared to a motor riser....

Happy Boating

Thanks! I think that's the route I would go.

Do you sandwich some wood inside that 5" riser?

 

[Sea Rider]

Thanks! I think that's the route I would go. Do you sandwich some wood inside that 5" riser?

You're welcome,
Never done that, but you are free to so so, will probably add a much tougher support riser/ transom when plan using a much heavier motor. Once right at middle bolt both side and lower hoizontal metal plates with a long screw and nut going through the metal transom, add SS washers if liking same as when bolting a motor to the transom.

Happy Boating​

 

[Faztbullet]

Slap a mini jack on it and go...will be cheaper and stronger than that a fab one.

Amazon.com

 

[BWR1953]

I remember those mini-jacks. I think they're only rated to 35HP.

 

[roscoe]

Post 1 says both motors are 15".
Post 6 says 20".

If the 40 is a 20", just spend $200 on an adjustable jack plate and be done with it.

KUAFU 4'' Set Back Jack Plate​

 

[Christian68]

Post 1 says both motors are 15".
Post 6 says 20".

If the 40 is a 20", just spend $200 on an adjustable jack plate and be done with it.

KUAFU 4'' Set Back Jack Plate​

I think the moderators merged two of my threads together or I screwed it up, lol. That's why it's confusing. The seller of the 40 merc said it was a short shaft. Turns out it's a long shaft so now I'm seeing what my options are before buying it.

If a simple jack plate is the answer and not a sacrilegious thing to do then I can still consider the 40 merc. I honestly didn't realize people put 20" shafts on 15" transoms. Now I know it can be done.

Thanks.