Is 1994 force 90 powerhead compatible with a 120 powerhead

[Buffers]

I bought a 1994 donzi jet boat with a 90 horse force motor, I thought it was a mercury because of the owners manual said mercury. Went to get parts at the Mercury dealer, they told me it was a force motor and that is what they used in the donzi jet boats. Now to find out the motor is not good, and I need to replace the power head.
My question is......
1. I am having a hard time finding a 90hp force power head, plenty of 1980" 85hp and plenty of 1990's 120hp but not 90 horse powerheads
Will any of these 1980's 85hp or 1990's 120hp force powerheads have the same bolt pattern to bolt back on to the jet.?

I am looking at a1996 120 force outboard, someone told me I could remove the power head and use that because it has the same bolt pattern. The 120 is a 4 cylinder and the 90 is a three cylinder, seems it would be bigger
I am also looking at an 1988 85 horse motor and would like to know if that would be compatible ?

 

[roscoe]

The motor is a Force model, made by Mercury.
The Merc dealer is the place for parts, aftermarket suppliers have parts too.
BUT.... many parts are no longer available at all.

Probably better off repairing the powerhead you have.

What is wrong with it?

You will run into many issues trying to swap powerhead, crankshaft size, clearance issues, there were many changes between models and years in the 90's, as Mercury was making Force motors with spare parts they had laying around from different motors.

I hope you don't have much money invested in that rig, as it will only get wor$e and may never run.

 

[Buffers]

Hello rosco,
Thank you for responding..
Not a big investment, about a $1000.00
The trailer is worth I think between $7-800.00
I sit here now thinking what ever made me buy this.... lol
Next week I m going to get a quote on rebuilding the power head and if it is to crazy of a price, I think I will donate it and hopefully someone who is more mechanical than I am can make it work

 

[roscoe]

I hate to bear the bad news, but better than having false hope.

Do you know what is wrong with the current powerhead?
Compression loss?
Cylinder or head damage?

It could be something relatively easy to repair, unfortunately, most places willing to do a "rebuild", will only do a full blown rebuild, and that will be costly.

It it is just a head gasket, or a single piston with no major cylinder damage, not bad.
Ignition issues are relatively easy to repair, but diagnosing the bad part(s) can be difficult some times.

Cylinder damage, bad crankshaft, and electronics meltdown..... that is just too costly to justify, especially if you are paying a repair shop.


There are powerhead that will work for you, but I am no longer in the loop, so can't tell you which ones to look for.

 

[jerryjerry05]

.
The parts for almost everything is still available.
Except for some parts for the L drive Force.

These motors are easy to work on and aren't that expensive.

Yes the 120 should swap.
But I think it needs to be a 94 and up block.
Mercury used their parts on the Force block.

You need to post the model # serial# and anything else to help ID the motor.

Some people don't like Forces and have a low opinion of them.
Mercury thought they were good enough to put in their Sport Jets 93-98

Figure out what's wrong and post that.

On your profile, fill it out and add you location and boat info.
You might be close t someone who

 

[Buffers]

Thanks guys,
This information is very helpful.
a learning experience at best... lol

 

[jerryjerry05]

You have 2 posts on the same thing.
Maybe have a mod combine them?


You still haven't said what's wrong with the one you have?
Fill out the signature and location.
You might be close to someone who can help or even rebuild it??

 

[Buffers]

It turned out to be a bad head gasket, did a compression test, 125 in all three cylinders. Also needed a new ignition.
Starts right up.
I put in the water yesterday and could not get the boat over 5 mph. The mechanic that worked on it thought the impeller looked good when he inspected it. He said I should change the spark plugs, I probably should have done that before putting the boat in the water

 

[Redbarron%%]

What rpms do you get in the water?
it should rev to 4800 - 5200 WOT.
If it is revving and not moving then the wear ring and impeller may be worn out.
Google JB weld build up for the wear ring.
I have a Hobie Jet with the 90 and it runs 30+ mph and turns ~5000.
Of course it is a fishing skiff and probably not originally as fast as the one you have if both like new.
The drive system is fairly straight forward and reliable, if properly maintained.
Check the lube in the gearbox and the stator to make sure you don't fix it only to have it seize up.
If it won't turn over 3000 then it won't plane out and you may be running on two of the three cylinders.
I used a timing light clamped over the spark plug wires while powered up to find the not firing cylinder.
My Hobie will cruise at 4200 fairly level and 25 mph, but tends to want to settle in around 4000.
Low RPMs is just not enough to get out of the hole.