1973 Mercury 85hp lower unit

[benhawk]

Ok, I am sure this topic has been discussed plenty of times, however I had no luck finding anything under the search option.

What lower units are compatable with an 1973 85hp Mercury? I need a new lower unit as both of mine are gone (I have two motors one working, and one for parts). I would like to know the range of years.

If anyone is looking to get ride of a working lower unit please let me know.

thanks.

 

[Chris1956]

Re: 1973 Mercury 85hp lower unit

That motor has a 2.3::1 gear ratio. That was found on only inline four motors, and one of those is the best replacement. I do not know the range of the years however. Most any inline 4 or 6 cylinder gearcase from the early 70s to the late 80s, will fit. Most have a 2::1 gear ratio. I swapped the gearcase off my '77 Merc 1500 to my '73 Merc 850. I used a prop with 2" less pitch to make up for the gear ratio change. Where are you located? I still have parts for both motors.

 

[benhawk]

Re: 1973 Mercury 85hp lower unit

Thanks for the info. I am located in So. NH.

I found a '77 115hp Merc close by, which the owner claims the lower unit is good. I am going to check this out on Saturday.

As for checking the lower unit, is it as simple as moving the shift lever into forward, neutral, and reverse and spinning the prop? When in forward the prop should "ratchet" in the opposite direction, and same when in reverse? And in Neutral the prop should "free spin", am I correct in assuming this? The motor is not installed on a boat.

Thanks!

 

[Maxz695]

Re: 1973 Mercury 85hp lower unit

The prop locks in both directions in reverse. It locks one way and ratchets the other in foward gear, and it spins freely in both directions in the neautral position. Then you have to make sure he cam is aligned correctly 1) High spot R <-^ in neutral is left of the front center of the LU 2) Mid lift on cam N ^ is center of the front of the LU that faces the boat, and the Low side of the cam F ^->is to the right of the front center of the LU^. This is what it should look like in Neutral R<-N^F> N is Center front of the forward point part of the casing facing the boat ^ <-^-> R N F R Hi spot of the cam N is Mid dentent F Low spot of the cam

 

[Chris1956]

Re: 1973 Mercury 85hp lower unit

Max is correct about the behavior of the gears, however, I do not think there is a good test you can perform on the gears w/o being under load. It will be a crap shoot until you test on your motor. Be prepared to use a prop w/ 2" less pitch

 

[benhawk]

Re: 1973 Mercury 85hp lower unit

Thanks for all of the help.

I picked up the motor this weekend, and all is good. Lower unit works in all three gears, and sounds good.

I was thinking of leaving the original prop on (the one that came w/ the 115hp) however I am not sure that is a good idea.

What will I notice with this prop? I konw that is a hard question to answer, as I am not familar with the different types of props available and not sure what type is on the motor at the moment. Do you think I would be better off putting the prop from my 85hp motor on?