Cut off top of driveshaft? 1992 90 mariner with 2004 mercury lower unit

[incharleston]

I bought a lower unit for $100 from a guy that wasn't sure if anything was wrong other than seals leaking a little. Drained and filled ...all seems fine.
Looking at the two lower unit side by side they are nearly identical except this LU has a 3/8 inch longer driveshaft. I believe the difference lies in the fact the old LU has the preload type driveshaft with the pin on top (although mine is missing)
I have tried mounting the new LU but it won't go all the way. 3/8 inch short of mounting
Would it be OK to cut 3/8 inch off of the driveshaft?

 

[Faztbullet]

Re: Cut off top of driveshaft? 1992 90 mariner with 2004 mercury lower unit

I believe the difference lies in the fact the old LU has the preload type driveshaft with the pin on top (although mine is missing)

If your correct on year models yours never had the preload pin..... and it being longer makes it from a DI engine. Check the gear ratio to see it they are the same.

 

[incharleston]

Re: Cut off top of driveshaft? 1992 90 mariner with 2004 mercury lower unit

Thanks for the advice. I will attach 2 photos for you to look at. Maybe this will help in deciding if I can cut the top of the driveshaft off.
By the way, what is a DI engine?
Oh and from my research I think the gear ratios are a little different but I was told swapping to a different pitched prop would help.

 

[Faztbullet]

Re: Cut off top of driveshaft? 1992 90 mariner with 2004 mercury lower unit

That unit is off a 4 stroke not a DI (Optimax)..If it is the 2.07 ratio your can drop a couple of pitchs to get rpm back but it will be a dog if you try to pull a skier as engine cannot build up rpm quick enough..