Are Force 85 & 125 components compatible?

[BWSmith]

Hi, everyone,

I have a Capri 1700 on which I'm running a 1987 125. The guy I got it from some months ago also threw in the 1989 Force 85 he had. The 85 needs powerhead work, but I took it anyway.

Running my boat recently, It dawned on me that the shaft is pretty long and the prop hangs well below the keel. Upon comparing it to the 85 I still have, there is a difference of five or six inches when measuring from the prop shaft centerline to the base of the powerhead.

As a result of this, I seem to be dragging the engine frequently in Charleston Harbor during low tide.

I have looked at the various options such as jack plates and just filling in the transom notch to raise the mount. All these seem either too expensive, complicated, or too unreliable.

Next I wondered if I can simply swap the powerheads and use the 125 head with the 85's lower unit. It seems to be in good shape. Are there any opinions on this matter? I am open to ideas as I think my boat will perform better with less mass hanging in the water. Not to mention that it seems to sit pretty low to begin with.

Thank you for your insight and guidance.

Bryan

 

[Dave K.]

Re: Are Force 85 & 125 components compatible?

brian, i'm not an expert & cannot say anything about the LU swap. my concern would be the rating for your boat. i have a 1600 rated for 90hp. it's possible your 1700 is rated for 125hp but from what you say it sure doesn't sound it. their may be a coast guard rating just under the dash..that's where mine is. it's also possible the 85hp was the original motor & rather than fix, he replaced w/ the 125. could be a legal problem or perhaps a bit dangerous. anyway, frank A, rritt, jerry, or roscoe can tell you for sure about the powerhead switch. gd luck..

 

[jim_b_20653]

Re: Are Force 85 & 125 components compatible?

Sounds like the 85 is a 20" shaft and the 125 a 25" shaft. You should measure your transom to see what length shaft you actually need. If you have a 25" shaft outboard on a boat designed for 20" your performance will suffer. To your original question, yes the 125 powerhead will bolt on to the 85 mid section. What I dont know is if the lower unit was designed for the extra power.

 

[DJ]

Re: Are Force 85 & 125 components compatible?

Big difference.

Fist off, the 125 is a four cylinder. The 85 is a three.

As for transom height, the 125's were offered in 20" and 25".

Figure out what you have.

 

[timdan94]

Re: Are Force 85 & 125 components compatible?

from what I've been reading the only difference between the two besides the power head is the gear ratio.

 

[DJ]

Re: Are Force 85 & 125 components compatible?

That I can't help you with.

Good luck. Realize you're talking about TWO entirely different animals.

 

[RRitt]

Re: Are Force 85 & 125 components compatible?

The exhaust gasket, spacer plate, motorleg, and lower unit are the same on 1989 85HP and 1989 125HP. You can put a 125HP powerhead onto an 85HP driveleg.

I would guess same goes for putting '87 powerhead onto '89 driveleg. check to see if both of the motors that you have use the same part #'s for powerhead mounting plates, motor pans, etc. etc.

 

[BWSmith]

Re: Are Force 85 & 125 components compatible?

Guys, I did take some rough measurements to check the relationship between the antiventilation plate and the keel bottom, and the AV plate sits well below the keel. The legs measured a difference of five or so when taken from the prop shaft centerline and the base of the powerhead.

As Dave above suggested, I think the guy I bought it off stuck on the 125 in lieu of the troubled 85hp rig. Max rated power for the 1700CR is indeed 85. I have been running the boat with the 125 for months and it seems to run nicely, except for the occasional bottoming-out of the motor keel during low-tide. I am not the reckless sort, but sometimes a little bit much power is better than too little. Any ideas on how this boat will run with FORTY less horsepower on tap? I'm sure I'd use less fuel. I have a small family, so I don't overload the hull.

My options seem to be to swap the lower leg and powerheads, or spend the winter working on the 85. I was told it needs a water pump and head gasket, and now a starter as I removed it for use on the 125. Thanks for all of your input and response. I am a longtime boater, I just never gave much thought to the rating on the placard and the issues that arise. After all, how to those little bass skiffs get by with 250-300 horses and around 80mph on the top end?!

 

[jerryjerry05]

Re: Are Force 85 & 125 components compatible?

Most of the parts are interchangable.The boat came stock with an 85hp. The change would work.The gearing in the lower unit is different and the performance would suffer.
If you really want to change things move the powerhead to the 85 base.Then swap the drive shafts.You will need special tools to work on the lower unit.Jerry

 

[jim_b_20653]

Re: Are Force 85 & 125 components compatible?

I think you will be surprised how much better the boat will perform with the correct length motor. I think you should use the mid section and lower unit from your 85, and either rebuild the 85 powerhead, or install the 125 powerhead. You may have to experiment with prop size and pitch due to the different gear ratios in the lower unit.

 

[RRitt]

Re: Are Force 85 & 125 components compatible?

I think you will be surprised how much better the boat will perform with the correct length motor. I think you should use the mid section and lower unit from your 85, and either rebuild the 85 powerhead, or install the 125 powerhead. You may have to experiment with prop size and pitch due to the different gear ratios in the lower unit.

my thoughts exactly. It should be an easy project but probably end up needing new prop.

 

[BWSmith]

Re: Are Force 85 & 125 components compatible?

Wow, Guys!! There seems to be more to this swap than I thought. I'm reasonably mechanically-inclined and am competent enough to handle this kind of work, plus I have the Clymer manual. I got spoiled on the extra power of the 125 and would like to stick with it.

I had not thought of the difference in gear ratios. It was suggested that I swap out the shafts. They are all compatable as well? That would certainly affect prop choice. Does anyone have any insight on the gear ratios of these engines? If I simply swaped-out powerheads and left everything intact, could I simply go with the maximum prop that would fit? I imagine the stock 85hp system is geared lower than the 125 due to reduced torque. This would seem rational, but these things in practice are often different. Initially, I was gonna go with a simple jack plate, but I want lighter as well, instead of just raising the assembly.

On another note, any thoughts on expected performance with a rebuilt 85? Any insight on how to boost output a bit. I think I'll like the lighter package better, but want max performance. I think I was getting about 32kts or so with the 125 long shaft hanging several inches too low. My reasonable side says to strip and rebuild the 85 and stick with that. This will take a bit of time and expense and more than likely will be the winter project.

Thanks again, guys. I'll be on the lookout for your input.

Bryan

 

[RRitt]

Re: Are Force 85 & 125 components compatible?

Composite reeds should boost power and improve gas mileage. But force engines have a tendency to cold sneeze which can eventually cause cracking in composite reed valves. If left unchecked cracked reed valves can lead to burned out powerheads. Boyensen reed valves are relatively cheap and should make a noticeable boost. Just make sure to inspect and/or replace them every few years.