1984 Johnson 40 hp lower unit

[LIVIT]

I have a 1984 40 HP short shaft on a 1986 alumacraft mv 16. Engine was running great, was running up on plane and motor vibrated violently. Shut down, electric motored in. Checked lower unit fluid and it was black and rather stinky. My local dealer claims that whole lower unit is shot and not easily replaced and that it would be very expensive. They are trying to get me too purchase a used 70hp long shaft and use a jack plate or rebuild my transom to use a 20 inch.

I personally feel that this is a bit too much engine for a 16' foot boat, even though from what I have read about this boat, they were originally rated for 40-70 hp, but that did not include a jackplate and power tilt and trim, all that would add around 300 lbs more than my 40 hp set-up.

My question is .... is it true that my 40 hp that really runs great still is now unusable ? I have shopped for a complete lower unit and have had no luck. Any suggestions or sources etc will be greatly appreciated.... tks

 

[juno pierrat]

black and stinky oil normal if not changed for a long time, parts available, any shiny metal flakes or chunk of metal in oil

 

[racerone]

Most of them were sold as long shaft.----So the short ones are rare.-----Try searching for ----evinrudeparts.++----They may be of help.

 

[LIVIT]

Juno, yes some shiny flakes. Oil was not that old. I did drain and put fresh in and it looked bad when I drained it again.

racerone tks buddy, had not thought of that. I was told the short shafts were rather unique, seems they were used commonly on the Alumacraft boats like mine. Transom was even cut with a U to use a short shaft ?

 

[LIVIT]

If I put the motor in gear, I can turn prop then it catches on gears and I can almost turn the motor over. If that helps any. Seems to me that it has sheared off just some of the teeth on a gear. I am mechanically inclined but not on outboards

 

[flyingscott]

First thing is your dealer is correct about the expensive lower unit ,and your motor not worth fixing. Second thing is take your lower unit apart, at a minimum you want the driveshaft and shift shaft to be good. You can buy a longshaft lower unit and convert it to a shortshaft with your parts. That is if you are absolutely bent on fixing it. The 70 hp will not add 300 #s to your boat, it will be closer to 75#s. Your 40 hp is 200#s roughly, a 70 hp with tilt and trim weighs about 250. Build your transom up and forget the jackplate.

 

[LIVIT]

flyingscott, tks for that info. Dealer offered me a good deal on the 70 $1500 for motor plus install of a couple hundred. Now I will have to see about getting transom built up. Again tks all, sure has helped me set a course I am more comfortable with.

 

[interalian]

I personally feel that this (70hp) is a bit too much engine for a 16' foot boat,

I have 140hp on my 16' aluminum boat. It's just about right. For me...

 

[LIVIT]

Wow I bet with a 140 that boat really scoots. My 40hp pushed mine with 2 people at around 30 mph according to my Helix 5 GPS, which I was comfortable with. Makes me wonder just how much more speed this 70hp is going to produce. Plus I am going to have tilt and trim now, which I for sure am going to appreciate that tilt feature !

 

[interalian]

Pushing 50mph (GPS) with two people at 3300' elevation. Hate to thing what it would do on the salt.

Note: it's a decked sport boat, not an open Jonboat. Came with a 90hp in 1983 and I rebuilt the 90 using a 140 block and other parts 2 years ago. I kept the 90 lid, because, well, you know.

 

[LIVIT]

Ok now I see, you have a lot more hull than I do. Mine is just a little side console bass boat. Still 50 mph is scooting along nicely in that size boat. At this age (61) 50 mph on the water would be more than fast enough for me. Thats a nice looking older boat, I been slowly working on mine. Once I get the engine issue fixed, I am going to start replacing some of the decking and carpet. I think its worth it, I really like the size for the local lakes and rivers.