Exchanging Mercruiser 165 with a 120 Hp

R

rp2pierce

Recruit
Joined
Jul 4, 2009
Messages
1
I had to pull my 1975 Mercruiser 250 ci 165 hp engine because of a large crack in the block causing water to poor out. I found a rebuilt Mercruiser 1963 120 hp complete engine. Will the 120 block slip right in. I worryied that sence what was in it was an inline 6 and the 120 is a 4 cylinder, that the length would be to short for the mounting brackets and the driveshaft will not interchange. Does anyone have information on this?
 
Bt Doctur

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,542
Re: Exchanging Mercruiser 165 with a 120 Hp

It should, may have trouble with the exaust Y pipe fitting correctly,The gear ratio in the drive needs to be changed to 1.98-1 ,the new front mount needs to be glassed in place.
 
mkast

mkast

Lieutenant Commander
Joined
Nov 6, 2002
Messages
1,934
Re: Exchanging Mercruiser 165 with a 120 Hp

I might recommend looking for another 165. If you are going to go through the work of replacing the engine, and changing the gear ratio, it can become costly. Bolting in smaller horsepower may come back to haunt you everytime you turn the key.
 
G

gadget73

Petty Officer 1st Class
Joined
Jun 20, 2009
Messages
308
Re: Exchanging Mercruiser 165 with a 120 Hp

+1 on replacing like with like. Junkyards may be a source for a donor 250 engine, but it will need to be marinized before use. Also there seems to be something about a front mount that has to be there. Don't know the specifics, but I've seen others talk about it before.

Also, if its a crack on the outside that is not allowing water into the oil system, you can just drill it at each end of the crack and pack it with JB Weld. I know thats a really hackish way to do things, but it might get you by for a while. If its making milkshakes in the crankcase though, forget it.
 
You must log in or register to reply here.
Top