1987 Force 85hp Powerhead Rebuild

[Isaacm1986]

So I picked up a 1987 Force 85hp for $200. I has 115psi in the top 2 cylinders and 40psi in the bottom one. I put a new head gasket on hoping that was my issue, but still the same readings. I am wondering what the next step is on this motor? The pistons look nice, and the cylinder walls all look clean and smooth, so i am not sure what would cause low compression in one cylinder.

Is the powerhead worth rebuilding? how good are these motors? just trying to figure out the best options here.

thanks.

 

[jerryjerry05]

Re: 1987 Force 85hp Powerhead Rebuild

Very easy to rebuild.
Some just remove the 1 piston.I don't.
If it's that bad to stop it from running then I want to make sure there is nothing going on in the next 2

Take the side covers off and check the damage on the piston.It could be just a stuck ring.
If you have caught it before any real damage is done your lucky.
Most don't and ruin them.Then there is a rebore and new oversized oistons.
If it's just rings then you can reuse the piston.

 

[Isaacm1986]

Re: 1987 Force 85hp Powerhead Rebuild

Very easy to rebuild.
Some just remove the 1 piston.I don't.
If it's that bad to stop it from running then I want to make sure there is nothing going on in the next 2

Take the side covers off and check the damage on the piston.It could be just a stuck ring.
If you have caught it before any real damage is done your lucky.
Most don't and ruin them.Then there is a rebore and new oversized oistons.
If it's just rings then you can reuse the piston.

Does doing a decarb make make sense when the compression is so far off? Is there any other way to try and free a stuck ring?

 

[foodfisher]

Re: 1987 Force 85hp Powerhead Rebuild

That (decarb) would be my first step.

 

[brinker232]

Re: 1987 Force 85hp Powerhead Rebuild

Soak the cylinder, with the low compression with Marvel Mystery Oil. Bring the piston to TDC and fill it as full as you can. It will help clean out anything. I have used this trick on aircraft motors for years and if it's just a ring issue, this clears it up 95% of the time!!!

 

[Isaacm1986]

Re: 1987 Force 85hp Powerhead Rebuild

Soak the cylinder, with the low compression with Marvel Mystery Oil. Bring the piston to TDC and fill it as full as you can. It will help clean out anything. I have used this trick on aircraft motors for years and if it's just a ring issue, this clears it up 95% of the time!!!

Thanks. I will try this. Sounds like a good idea.

 

[jerryjerry05]

Re: 1987 Force 85hp Powerhead Rebuild

The stuck rings are usually solid carbon buildup.
I love MMO but find it useless on these outboards.
If the #s were 120,120,100 I'd go with a decarb.
But as far as these #s go it's gonna need work.J

 

[Isaacm1986]

Re: 1987 Force 85hp Powerhead Rebuild

The stuck rings are usually solid carbon buildup.
I love MMO but find it useless on these outboards.
If the #s were 120,120,100 I'd go with a decarb.
But as far as these #s go it's gonna need work.J

Well if the mmo does not work I will start to tear the power head apart

 

[Isaacm1986]

Re: 1987 Force 85hp Powerhead Rebuild

Ok I concede. I did the mmo, and the decarb with the sea foam. still the same readings. So i am going to begin to tear about the powerhead.

Does anyone have a walk through for replacing that piston ring? Best way to do it?

thanks.