reasonable expectations

[redfury]

I'm buying my neighbors 86'ish Force 125 for 500 bucks ( He upgraded boats and is parting his Bilgeliner bass boat out ) and I happened across old literature from Mercury. It showed my exact boat, with a 65, 85 and 115hp Merc ( tower of power ) with performance specs. Loaded with 4 people, they claimed 40.9mph and 43 with one person.

My 'tron is rated for 125hp, but based my assumptions that the mercury motor is lighter than the Force and obviously a different design-from an engineering standpoint, would I be reasonable to expect similar performance out of the 125?

 

[Frank Acampora]

Re: reasonable expectations

First off, I am almost certain that the Merc is heavier than the Force. The merc was also under-rated by a significant amount. The Force 125 is not an engine that performs as well as the Force 120. I suspect that if you get 35-39 MPH you should be happy.

To illustrate the point: I have a 140 HP chrysler on a 21 foot deep vee cuddy. On a good day it will get 39 MPH with just myself in the boat, most times it goes 36. I recently worked on a Merc 100. On a test drive it moved a round bottom 21 foot cuddy with three people in it at 39 MPH. Can you tell me with a straight face that that engine was only making 100 HP?

 

[redfury]

Re: reasonable expectations

Y'know, I remember watching a video of the old Kiekhaufer motors and the racing Mercury did back in the early days where they broke the 100hp barrier and then hit a record speed run. I seem to recall something being mentioned that the HP numbers were reported on the "conservative" side, so I would agree with you on that.

I went and took some pictures of the motor and pulled the model/serial numbers...it's a 1987 motor, a "B" model from what I was seeing, but can't seem to determine what the difference between the A and B models would be...power tilt?

My impression was that the Mercury motors were built out of lightweight alloys vs what a person would think of with the Chrysler/Force motors, but then again...it wouldn't make much sense to build what is essentially a performance motor out of cast iron...I dunno, my knowledge in this area is severely lacking.

Either way, the one thing I like about this motor is the relative ease of access to parts ( on the motor itself ) and simplicity in design. Sorry, Mercury's throw my head for a loop when I crack the clamshell on them...the Force is well marked with color coded diagrams. It's like Sony built "My first Outboard" Anyone with reasonable mechanical acumen should be able to tinker with the motor with some relative success IMHO.

I was kinda hoping to take some of the guesswork out of propping the motor by using the same prop they used on the 115 ( 19 cupped ) on the 125, but I suppose lower unit gear ratios are never created equal...sigh.

 

[redfury]

Re: reasonable expectations

You mention that the 125 isn't as good of a performer as the 120...why? Reed valves, carburetors? I'm assuming the base engine internals are the same between the two motors...

 

[Frank Acampora]

Re: reasonable expectations

I should qualify that: Chrysler, and later on, Force, used two basic block designs. The blocks were exactly the same but one had larger sleeves it it to accomodate a bigger bore. They also used two different crankshafts. The Chrysler 125 and 140 had a "stroker" of 2.875 inches. Force continued the Chrysler 125 with no change.

The 125 is a 2.875 stroke by 3.3125 bore. The later Force 120 is a 3.375 bore by 2.80 stroke while the earlier 120 is a 2.80 by 3.3125.

With the larger bore and shorter stroke the late 120 has about the same displacement as the 125 but really produces a better power curve and usually will equal the 125 in speed.

At about 275-300 lbs, the Force is about the lightest engine made in that class. Yes, much simpler than OMC or Merc and the cowl design was cleaner and better looking.

BTW: Before you ask, YES you can swap a 2.875 crank into a later Force 120 to get a 140 BUT you must raise the ports about .07 (about 1/16) to gain the horsepower.


Here's a photo of my 140, my 105 with mermaids, and my V153 with a hot Chrysler 75.
The avatar is the 105 on a 15 foot Glastron V153. It tops out at 45. It is perked-up a little with a 2 to 1 lower unit gear ratio. You can also gain a bit out of the 125 by swapping in a 2 to 1 in place of the 1.76 to 1 ratio and going up 2 pitches on the prop.

There are really only minor differences in the A and B models, Might just be different model carbs or that might be when they went from quick-connect fittings on the ignition to terminal board wiring, but just about everything will swap.

 

[NYBo]

Re: reasonable expectations

I went and took some pictures of the motor and pulled the model/serial numbers...it's a 1987 motor, a "B" model from what I was seeing, but can't seem to determine what the difference between the A and B models would be...power tilt?

All Force 125s of that vintage had power trim and tilt.

 

[redfury]

Re: reasonable expectations

Well, that all makes perfect sense to me. I guess if I ever have lower unit problems, I'll search for the 2 to 1 ratio LU instead of the stock one.

This picture is the only thing that has me perplexed about this motor, care to speculate?

I do like the fact that there is a lot of interchangeability amongst the Chrysler/Force motors. I could have picked up a 73 120hp Chrysler for $350 a month or so ago if I hadn't had the offer from the neighbor to buy his at such a good price ( and piece of mind buying a good KNOWN motor ).

 

[redfury]

Re: reasonable expectations

All Force 125s of that vintage had power trim and tilt.

Well, then I can cross that off my list of differences between models

So, this is a TRIM as well as tilt unit? I know the 115 Charger I bought for $20 with a bad cylinder had a trim sensor, but I didn't know if it was something that Chrysler did on their motors...I've heard of Tilt w/o trim, and it's always been something I question when I hear someone talk about t-n-t.

 

[jerryjerry05]

Re: reasonable expectations

The 3 screws are,fill and vent the third is a DO NOT TOUCH!!! The drain is under that screw on the bottom.It might be painted over.Look for it.
The a/b/c denotes small changes on the motor and trim system.Like connectors and small changes.
That color Force started in 87.Post a pic of your motor exhaust and ignition side.J

 

[redfury]

Re: reasonable expectations

The 3 screws are,fill and vent the third is a DO NOT TOUCH!!! The drain is under that screw on the bottom.It might be painted over.Look for it.
The a/b/c denotes small changes on the motor and trim system.Like connectors and small changes.
That color Force started in 87.Post a pic of your motor exhaust and ignition side.J

So, is that small hex screw the drain? He couldn't get it out of his boat, I was under the assumption that it was the screw that you didn't touch.

 

[Frank Acampora]

Re: reasonable expectations

That silicone filled hole is where the shift pivot screw is located. I always recommend filling the hole for that screw with silicone RTV. It keeps you from accidentally removing it and it is extra insurance against a water leak there. See? It works! It kept you from taking it out before asking.

 

[jason32038]

Re: reasonable expectations

Yes the very bottom hex screw is the drain. Mine was stripped so I found a torx bit large enough and hammered it in the screw and it came out thankfully.

 

[redfury]

Re: reasonable expectations

Who the hell designed that as a drain? Wow, that's a tiny drain hole. Guess I'll have to get that out of there and replaced with a better screw.

Anyone else have suggestions on dealing with this thing as far as getting it out? I'm not too worried about drilling and tapping this since anything that gets up in there is going to come out of the hole as the residual oil drains ( not to mention it wouldn't be too difficult to flush ).

 

[jerryjerry05]

Re: reasonable expectations

I use a torch.Just a little bit of heat.Make sure the vent screw is open a bit.
I also fit in an allen head driver socket not the usual wrench.I tap it with a hammer.Do not over do the heat or tapping.
Those fail or you strip the allen head then a drill and easy out.J

 

[Frank Acampora]

Re: reasonable expectations

That is a standard 5/16 set screw. There is PLENTY of meat where it is located. If you want to re-tap, you can go to a 3/8 X 16 and spotface to take the regular plug like the fill and vent. You can also tap out to 1/8 NPT pipe plug. There is enough aluminum that if needed, you can go up to 1/4 NPT.

 

[redfury]

Re: reasonable expectations

Excellent. I'll be sure to do that. I wasn't too worried about the amount of metal in that area since it takes a bit of stress, but it's nice to have that verified. Too bad though, he had the LU off this summer for the impeller replacement...could have done it then.