Will a 1969 1000 merc lower fit on a 1979 90hp if they both are short shafts?

I found a local 1969 1000 merc motor with a good lower unit. I have a 1979 90hp in need of a lower unit.
Will they bolt right up and if so will I need a different prop?

My1979 90 Hp Serial number is 5220684
His 1969 1000 Serial number is 2573572
Thank you for any input

Re: Will a 1969 1000 merc lower fit on a 1979 90hp if they both are short shafts?

Anybody? Or any website I can go to find this info??? thank you very much!!

Re: Will a 1969 1000 merc lower fit on a 1979 90hp if they both are short shafts?

The gear housings are quite different. If the bolt holes line up and the splines on the top of the drive-shaft are the same, then it will bolt on. There are also the issues of shift shafts and if the older engine has electric trim. I suspect this will be a 'suck it and see' exercise.

Chris........

Re: Will a 1969 1000 merc lower fit on a 1979 90hp if they both are short shafts?

I bolted a 1973 85 merc lower unitn onto my 1979 90hp merc motor. It all works fine. I need to get a differnt prop. (still trying to understand what will be the right one though)

Re: Will a 1969 1000 merc lower fit on a 1979 90hp if they both are short shafts?

If the prop you had on the 90 hp previously was perfect, then you will find that with the 2.3:1 gear ratio of the 85hp L/U, that the motor will have more "hole shot" and rev up faster, but probably won't have as high of boat speed.

So, if this is the case, you would want a prop that has 1" or 2" more pitch than the one you had on your 90hp.

This is about as close as we could estimate, far as effect of changing the L/U goes.

Once you've run the boat on the water, you'll be able to tell how it all works. If the motor sounds like it's revving up too much, or you've lost a lot of boat speed, then you'll know that prop selection isn't quite right.

If you have a tach, more's the better, your 90hp makes best power around 4800-5000 rpm and doesn't like to "spin up" much higher than 5K.

HTH.........ed

Re: Will a 1969 1000 merc lower fit on a 1979 90hp if they both are short shafts?

If its a 1000SS ....yes it should fit.