Mariner 115 lower unit gear housing

[Mastermind1973]

I have a 1987 Mariner 115 6 cyl. inline..I have managed to puncture a hole in the lower unit but there appears to be no damage to the internal parts. I am searching for a replacement lower unit. Does anyone know what years, brands, and/or horsepowers are interchangeable with this particular motor?? For instance, I found a 1987 Mariner 75 in pristine condition and the lower unit looks to be exactly the same as the one on my 115..only difference is obviously the powerhead. Any advice would be greatly appreciated. Thanks!!

 

[jimmbo]

Re: Mariner 115 lower unit gear housing

The four cylinder 75hp, 80hp, and 85hp gearcase will fit. They do have different gear ratio, 2.3:1, than the inline 6 model. Since 1973 almost all inline sixes used 2:1. You will need to go up in pitch a bit to compensate. In the mid 1980s, the 2.3 case was offered as the High Altitude option for the inline 6s

 

[Mastermind1973]

Re: Mariner 115 lower unit gear housing

Thanks, jimmbo for the info. To be safe, I think my best bet is to replace the lower unit since I'm not sure the exact damage that may have been done internally. I'm not super boat saavy, but I'm figuring that you're talking about the pitch on the prop?? What would be the result if I did NOT change the pitch and went with a 2.3:1 ratio from a 75 HP??

thanks

 

[jimmbo]

Re: Mariner 115 lower unit gear housing

the engine would rev higher, and your holeshot would be quicker. What rpms were you getting prior to the damage?