40hp Lark powerhead to 18hp fast twin leg

[gusthewonderslug]

Hi all
Is it possible to graft a lark 40hp power head onto a fast twin bottom end.
Gus

 

[racerone]

Re: 40hp Lark powerhead to 18hp fast twin leg

With a truck load of time and money I suppose it can be done.------------Certainly not in one afternoon.

 

[F_R]

Re: 40hp Lark powerhead to 18hp fast twin leg

Even with the load of time and money, not without a machine shop to create special parts. Sort of like putting a Chevy engine in a Toyota. Actually, the answer is no, it cannot be done. Two entirely different motors.

 

[HighTrim]

Re: 40hp Lark powerhead to 18hp fast twin leg

The 40hp legs are common as dirt, should not be an issue locating one. I trip on them all over my house and shop, lol

 

[jimmbo]

Re: 40hp Lark powerhead to 18hp fast twin leg

The Chevy into a Toyota is Doable and easier. The 18hp gearcase is not up to the torque of the 40hp

 

[F_R]

Re: 40hp Lark powerhead to 18hp fast twin leg

OK, I should have said a Mack Diesel into a Toyota Corolla

 

[gusthewonderslug]

Re: 40hp Lark powerhead to 18hp fast twin leg

Thanks Guys
Ok what is the most compatible bottom end for this powerhead then.
Gus

 

[jimmbo]

Re: 40hp Lark powerhead to 18hp fast twin leg

what year is your lark? that matters cause some larks were mechanical shift and later ones were electric shift

 

[F_R]

Re: 40hp Lark powerhead to 18hp fast twin leg

Early Larks had the old single wall exhaust housing, then 1958-up had the double wall (Super Quiet) bottom. Powerheads are not interchangeable between the two types. Later on, the bare powerheads were interchangeable between mechanical shift and electric shift.

 

[gusthewonderslug]

Re: 40hp Lark powerhead to 18hp fast twin leg

Early Larks had the old single wall exhaust housing, then 1958-up had the double wall (Super Quiet) bottom. Powerheads are not interchangeable between the two types. Later on, the bare powerheads were interchangeable between mechanical shift and electric shift.

Thanks guys it is a 68 lark.

 

[racerone]

Re: 40hp Lark powerhead to 18hp fast twin leg

Pictures of what you have or a correct model # is almost a must.-----------These motors are not " all the same "

 

[HighTrim]

Re: 40hp Lark powerhead to 18hp fast twin leg

Too bad you were not closer, Im having a "garage sale" of 60s 40hp motors, lol. Have a few out in the shed and sick of moving them around!

 

[gusthewonderslug]

Re: 40hp Lark powerhead to 18hp fast twin leg

Too bad you were not closer, Im having a "garage sale" of 60s 40hp motors, lol. Have a few out in the shed and sick of moving them around!

Guys the current details are it's an

Evinrude 40 selectric shift model number 40873c serial no. A 32337

I recently rebuilt the bottom end including bearings and seals and it is running like a top the problem is it sounds a bit rough in the bottom end I have now sourced the correct oil instead of ATF the stealer tells me they no longer import the correct oil!!! This has made the bottom end much quieter but I'm still reluctant to trust it and if possible would swap the selectroshift bottom end for a mechanical shift for peace of mind.
My other thought is to add some gearbox treatment like Stp or wynns or similar to see what that does.

 

[racerone]

Re: 40hp Lark powerhead to 18hp fast twin leg

Gid you inspect / replace the tapered roller bearing in front of the forward coil ?-----How did you determine that the noise is coming from the lower unit ?

 

[gusthewonderslug]

Re: 40hp Lark powerhead to 18hp fast twin leg

Gid you inspect / replace the tapered roller bearing in front of the forward coil ?-----How did you determine that the noise is coming from the lower unit ?

Racer
Not sure if my last post went,
The bottom end sounds as though the pinion is engaging too deeply!
With the heavier / correct oil it's much quieter, but still not silent.
Maybe I'm worrying unnecessarily and the noise may be normal for this style and age of motor,
I would like to try an additive but I am concerned about increasing the viscosity and ruining the Electroshift mechanism,
I may just continue to run it until it dies but would rather see if an additive will make it quieter.
The reason for wanting to know what bottom end will suit is that if it does die I would simply swap my power head onto a mechanical shift bottom end.
The mechanics at the dealership has no interest in assisting as he has no knowledge of these old motors and if it ain't new it's not cool.
The current motor is the original on my boat and I would rather persevere with what I have instead of upgrading to a modern engine.

Gus

 

[racerone]

Re: 40hp Lark powerhead to 18hp fast twin leg

You did not answer the 2 questions !!!

 

[jimmbo]

Re: 40hp Lark powerhead to 18hp fast twin leg

Early Larks had the old single wall exhaust housing, then 1958-up had the double wall (Super Quiet) bottom. Powerheads are not interchangeable between the two types. Later on, the bare powerheads were interchangeable between mechanical shift and electric shift.

So what about when the electric shift and the Super Quiet double wall bottom was discontinued in 1971 and the 40 looked almost like a 1957 lark?

 

[gusthewonderslug]

Re: 40hp Lark powerhead to 18hp fast twin leg

Racer
Sorry.
I deduced the noise is coming from the bottom end as when I click into forward or reverse I get an audible "rumble" for a better word, when I accelerate the noise get louder, it doesn't sound like a failing bearing, I am a Fitter and First Class Machinist and have worked on all types of machinery from small to large over the years, it sounds like the gears are meshing too deeply or the back lash is incorrect.
yes I inspected the forward bearing by removing the forward electromagnet, I have also checked the prop output shaft and it doesn't seem to have excessive end float.
As I said I may be being too pedantic and it may be normal, I just don't have any reference point to compare it to. as I stated previously my local dealer isn't too interested in dealing with old motors.
Thanks for your assistance!

 

[gusthewonderslug]

Re: 40hp Lark powerhead to 18hp fast twin leg

Jimmbo
Im not too sure what your saying?
is there several bottom ends that will suit this power head?
Gus

 

[racerone]

Re: 40hp Lark powerhead to 18hp fast twin leg

The 1968 40 HP electric shift powerhead will fit on any 40 HP Johnson / Evinrude mechanical shift from say 1963 to 1970 models.