1973 40 Hp Lower Unit Swap

[AEROCOOK]

I have a 1973 Merc 40hp 2 cyl (7015410 Canadian) that needs a new lower unit. Found one for sale from a 3 cyl 65hp believed to be a 1976 but no serial number to confirm. Is there any chance that this lower unit will work on the 40hp?

 

[emckelvy]

Re: 1973 40 Hp Lower Unit Swap

The gearcases have essentially the same bolt pattern, but watch out for the (2) studs towards the front of the gearcase, sticking straight up.

Spacing on the 650 and 50/40 hp units may be different and you'll have a heck of a time bolting up if they are. Simple measurement will tell.

Note that some units also had a square-shanked shift shaft instead of a splined one. These can be changed-out, as the other end has the usual splines to engage the shift cam. But of course this adds more complication and expense to the deal. You might have better luck finding a 50hp lower unit, there's a lot more of them out there than either 40 or 50 hp.

HTH & G'luck..........ed

 

[AEROCOOK]

Re: 1973 40 Hp Lower Unit Swap

The gearcases have essentially the same bolt pattern, but watch out for the (2) studs towards the front of the gearcase, sticking straight up.

Spacing on the 650 and 50/40 hp units may be different and you'll have a heck of a time bolting up if they are. Simple measurement will tell.

Note that some units also had a square-shanked shift shaft instead of a splined one. These can be changed-out, as the other end has the usual splines to engage the shift cam. But of course this adds more complication and expense to the deal. You might have better luck finding a 50hp lower unit, there's a lot more of them out there than either 40 or 50 hp.

HTH & G'luck..........ed

Thanks for replying, I noticed in my forum search that a lot of lower unit compatibility posts go unanswered so a detailed response like yours is appeciated.
The 65 hp lower unit has the square shanked shift shaft but it has the shift rod with it so it can be swapped over if required. Im a little confused about the stud spacing issue you mentioned. Do you mean the length of the studs? Seems to me if the studs were in a slightly different position, they wouldent line up with the holes on the mid section?
Can you clarify?

Thanks.