Force 125 pistons?

[auchandler1]

Looking to swap out a powerhead with a bad cylinder for another powerhead that seems to be in working condition and I was told it was rebuilt. My question is the guy says it has 160 lbs of compression on each cylinder except 2 that has 157. I heard 130 lbs was really good but didn't know if they can get that high but i will check on that when i see it. My other question is I saw some pictures of it which I will put up later and the piston heads look a little black but seem to be in good condition. Now I don't know if this is a red flag saying stay away but I was thinking this is just normal since pistons deal with a lot of heat.

Thanks guys

 

[Frank Acampora]

Re: Force 125 pistons?

125 to 145 is the factory quoted spec on the 125 HP compression ratio. 160 does seem high but chalk it up to his particular gauge and the rebuild. On a fresh rebuild with assembly oil the compression ratio will be higher than after running the engine.

Black is just baked on carbon indicating the engine was run a little rich.

HOWEVER: Unless you are getting a really good deal on the other powerhead, why not rebuild yours? It only takes a little more work than dismounting the block--which you need to do anyway.

AND: If it is only one cylinder, boring costs max 60 bucks, piston is max 130 bucks complete with rings and wrist pin, and a gasket set will cost around 50 with the head gasket costing about 27. So, for less than 300 bucks you can have a rebuild. If you want to add more cylinders, add another 130 for each piston replaced and 50 for each hole bored. Still not a bad deal and you know the history on your engine.

 

[jerryjerry05]

Re: Force 125 pistons?

The color(black) is burned gas/oil.NO problem.
Compression on an outboard.It should be within 5% of each cylinder.
Different guages will read differently.
My tester $100 will read differntly than a cheap one.
Good compression on my guage for a Force is 150+.
The thing to look for is ANY scoring in the cylinder walls.
I bought a 88/125 for parts.Turns out it just needed a flywheel key.
I decided to sell the parts.I did a comp test and found 155# on all 4.
I had the powerhead sold and decided to remove the head to check(I won't sell anything that's bad)and found scoring on 1 cylinder.I didn't sell it.Gonna rebuild instead.
The newer Forces after 92 I understand the compression is supposed to be about 165#.Most manufacturers don't publish comp#s.
The thing to look for is being close to each other.

 

[auchandler1]

Re: Force 125 pistons?

 

[Frank Acampora]

Re: Force 125 pistons?

That looks about normal. I can see one or two cylinders that are running a little richer than the others but again, that is typical for these engines. One cylinder of a pair will always run just a tad richer. There is nothing that can be done to correct it.