force 85 outboard year range?

[tc313640]

What year range of force lower unit would fit the lower unit of an '88 force 85 outboard? And also are most of the engine parts are interchangable as well? Thanks

 

[Frank Acampora]

Re: force 85 outboard year range?

All the gearcases and shafts are the same from the Chrysler 1 piece lower unit (Early 80s I think) to about 1989 Force. The only difference is that the Force 85 and 90 had 2 to 1 gears and the 125 had 1.78 to 1 gears. Chrysler 75 and 85 had 1.78 to 1 gears and the 90 was the only engine with 2 to 1 gears. So: you have a whole bunch of lower units to choose from. Just be aware that the 1.78 to 1 gears will reduce your horsepower and top speed somewhat--even with a prop change to a lower pitch.

 

[QuadManiac]

Re: force 85 outboard year range?

Curious, Frank... If the gear ratio goes down by 11% (2 to 1.78), which would theoretically make the prop spin 11% faster at the same motor RPMs, why won't dropping pitch by 11% make up for it almost exactly?

 

[Frank Acampora]

Re: force 85 outboard year range?

Not really sure why---I suppose it has to do with the torque band of the engine. All I know is that when I went from a 2 to 1 with a 19 pitch prop on my 90, to a 1.78 to 1 with a 17 pitch prop, (trashed lower unit --could not find 2 to 1 gears.) speed dropped by about 4 MPH. And I figured out that theoretical speed should have been the same.

Conversly, when I went from a 1.78 to 1 swinging a 17 pitch on my 125 to a 2 to 1 swinging a 19, speed went up about 3 mph and rpm went up about 400 rpm. Of course, fuel economy went down.

Note that the speed difference was slightly more marked on the lower torque 3 cylinder engine--Thus my hypothesis

DISCLAIMER: This was on my boat. Engines behave differently on different hulls. You may see different results.

 

[Bigprairie1]

Re: force 85 outboard year range?

Ok guys, Frank particularly...time for me to wade in here with a lower unit question. You are undoubtedly the guy to ask.
I have a 1991/90hp force that I am going to rebuild over the fall. It has a cracked lower unit due to poor winter storage methods.
What lower units will fit this '91? ie: years and sizes? I noticed a couple on ebay that were close buy it looks like the water intake is in a different place than on the one I have.
I as well, will post a new thread showing this upcoming project and I am hoping for some excellent feedback to get me through it.
Supposedly the engine was running fine up until that point.
Anywhoooo, what do you think?

 

[Frank Acampora]

Re: force 85 outboard year range?

Sorry--Can't help. I know they changed to a 2 piece drive shaft in 1990. I also know that on my 1990 90hp (bought cheap with no lower unit and all wires to boxes and coils cut) I installed a 1988 lower unit and everything fit. Maybe you can infer something from that. That's the engine in the avatar. After that, I can not say. Someone else will need to chime in.

 

[Bigprairie1]

Re: force 85 outboard year range?

...well that does help on some level. My existing/working motor is a 1990/90hp like yours so I can always cross reference it to the 1991 I have. Knowing that your 1990 successfully adapted an '88 unit tells me to do some comparisons.
That said....the '88 unit you adapted to your '90/90hp...was it an 85hp unit? or?

 

[Frank Acampora]

Re: force 85 outboard year range?

YEP! 2 to 1 gears.

 

[MWBROWN]

Re: force 85 outboard year range?

Fellow Force Owners,

If you have some time, one can go to mercruiserpart dot com and look and the part numbers for the different year engines. Seems that would help also.

My two cents,

Mike