Will a 75hp engine block fit on my 90hp clamshell engine?

[pedroofn19]

My old 90hp outboard has really bad compression, and misfires all the time on one cylinder. The mechanic says it need a rebore, but there is no way I can afford that. I can get a 75hp engine block, with the pistons and crankshaft still in it for a reasonable price. WILL THE 75HP BLOCK FIT ON MY OUTBOARD????
Thanks for reading.

 

[Faztbullet]

It will fit but you will need to change lower unit to the 2:3:1 ratio for it to work correctly...

 

[pedroofn19]

Faztbullet thank you for your reply, is that gear ratio 2.3:1 ?
I have the Mariner service manual for my engine and it says "gear ratio 2.3:1 for 3 cylinder engines", and 2.07:1 for 4 cylinder engines.
My engine is a 3 cylinder so I guess the gear ratio should be 2.3:1, would you agree?
Please excuse my ignorance on this subject, and let me know if I am wrong.
Thank you.

 

[pedroofn19]

Sorry I forgot to say in my original post it is a 3 cylinder, 2 stroke, Mariner from the early 90s, the one with the clamshell engine cover.

 

[flyingscott]

Hello I could be wrong here but if its the 75 hp that shares the block with the 90 hp. You may be able to convert the 75 to a 90 do a parts search and should interchange.

 

[Faztbullet]

When you posted old I figured you had a Inline 6 90hp. Yes the 75 will bolt up just make sure it about the same year . The earlier models was 71.1 ci and the 1994 and up are 84.6 ci. The worst you could get is a 80hp motor

 

[pedroofn19]

I should have said all that in my first post. I have asked a lot of outboard mechanics and 99% of them said yes I will fit. Im sure both blocks were made within a year of each other. Thanks for the advice guys, it was very helpful.

 

[DavidMoore]

If my memory serves be well the only difference betwen the 75 and 90 HP versions of that engine is the 90 has bigger carbs.
Hope his helps.

 

[pedroofn19]

That is what I thought DavidMoore thank you. I have the carbs from the 90, so it all looks good. Thank god for that as I cant afford another engine. But swapping engine blocks will be a real challenge for me, but Im sure I will get it right in the end.
Thanks for all the helpful info guys.