1994 90hp to 1989 85hp powerhead

[Mrhempel2u]

I have an 1994 90hp force outboard that has no compression on #2 cylinder, I pulled the head and there was some cylinder scoring and a bent portion of piston , I also have an 1989 85 hp force , my question is can I remove the 90 power head and use the 85 power head with all the 94 accessories?

 

[jimmbo]

Powerheads may swap, but you need access to factory parts lists for both engines to see if parts will interchange.

 

[Nordin]

Yes the 85Hp power head would swap right on as long as the 90Hp 1994 do not has the Mercury style LU.

I think they started to use Mercury style LU in 1995.

To change over the ignition from the 94 90Hp to the 85Hp need some more work.
Think the 85Hp has Prestolite ignition (blue ign.coils and three blue CDI boxes) and the 94 has the Mercury Thunderbolt ign.system).
Then you need to pull the whole stator/trigger mounting base from the 94 90Hp and put it on the 89 85Hp.
Maybe you need to drill some new holes but not really sure because I have not done this my self.

 

[jerryjerry05]

Model#?? Serial#
Pics of the ignition, flywheel and the gear case.

Might be easier to swap the complete motors.
The transom clamps might be interchangeable?
The shift linkage might be interchangeable too.

Again the serial# for the 94 would help a lot.

 

[Mrhempel2u]

Spot on on the ignition systems , I’ll get pics and serial numbers today when I get home from work , I was hoping to just be able to use the stator and trigger from the 85 and change the connections to use with the 90’s ignition. The engines look virtually identical other than the carbs and ignitions. On a side note, I originally bought the 85hp to use the lower unit on the 90hp , which I have for a couple of years with no issue

 

[Mrhempel2u]

So I talked to a friend at my local marine dealership and he said that it looked like the piston ring locating pin came out ....... and the rings may have moved and that’s why I lost compression...... can it be as simple as putting new pistons in the 90hp motor ?

 

[Mrhempel2u]

[No message]

 

[jerryjerry05]

The crank for both motors is the same.
So the lower unit should work.

The wrist pin coming loose????
The rings moving??
I don't believe either one.

Pics of the damage show you need a bore job and new piston and rings.
Not an easy job.
If the powerhead on the older one is good?? I'd use that.

Rebuild: you need a factory manual for the right specs.