Did the 1989 Force 125 even have a flat top piston

[NEKFORCE]

I was given a motor, and the guy had the old piston that was supposedly in it the first time it blew up. It has a flat top like a snowmobile piston, not the raised dome like all force pistons i have seen. Did these motors ever come like this or did the shop give him the wrong piston from something else? I held it next to one of the pistons I believe to be standard size and it was quite a bit smaller. I know one sleeve has been bored but I don't believe the other three have. And I must say the difference in circumference is like a quarter inch. So I don't even think the sleeves were ever thick enough to overbore that much anyway.
Also could somebody post the numbers that are on the top of a standard Force 125 piston so i can confirm my other three pistons are standard size?

Thanks

 

[pnwboat]

I've never seen flat top pistons in the Force outboards. Standard diameter for the 1989 125HP piston is 3.312". The maximum size you can bore it out is .040" which gives you 3.352". That doesn't come close to 1/4 of an inch. Given that the piston is a flat top, and significantly smaller, I would say that the flat top piston was from a different motor.

The best way to determine piston size is to measure them with a caliper or micrometer. I may be mistaken, but the standard factory Force pistons may not have any numbers on them. There are many manufacturers that provided pistons for the Force motors through the years, so it may be misleading to try and determine size by looking at the numbers on the pistons. These motors have been around for a long time and the piston that are in the motor now may not be the original. Having said that, if you can post a picture of the top of the piston(s) showing the numbers, or tell us what numbers are on the pistons, someone on this Forum may be able to determine the size.

To be sure exactly what you have, the cylinder bores, and pistons should be measured. Especially if someone or some shop has been messing with it.

 

[Nordin]

There were no flat top pistons in Force engine that was from Chrysler design. Maybe in Mercury designed engines, but I have not worked with those jet.
Have no experience of those.

If it is a 125Hp 1989 the std bore is 3,312 in.
120Hp B and C models from 1990 and through the std bore is 3,375 in.
120Hp A model 1990 has 3,312 in std bore.

 

[NEKFORCE]

Thanks Guys, I will post those numbers. They could be aftermarket pistons. Possibly Wiseco. I could swear they said they were 3.312 when i looked last.
When i checked the bored sleeve and piston i saw that had been bored it 30 over. I have to believe that piston he had went to something else. It's why smaller. I was planning to check with a caliper tonight, but it's gotta be a 1/4 inch smaller around.

 

[jerryjerry05]

The standard piston didn't come with a flat top.
Oversized pistons come marked on top with the oversize on it.
​No marks? Not oversized.

Pics help a LOT!!

 

[jimmbo]

I think the shop pulled a fast one on him, and just gave him any old piston they had lying around

What's currently in there, crossflow pistons or looper flat tops?

 

[NEKFORCE]

Guys, I finally had the time to look.. the pistons says 3029PS STD G80F3N on the tops.

OK Figured it out! thats a wiseco part number! so they are standard size. 3029PS Wiseco Std. CHRYSLER FORCE Piston
New Old Stock
Old Part # 3029PS, New Part # 3129PS
Wiseco Part#: 3129PS
Product Type: Single Pistons
Description: CHRYSLER/FORCE MARINE 3312KD
Bore - Standard: 3.312in
Bore - Actual: 3.312in
Bore - Oversize: STD
Sales Conditions: Must use Bearing Kit W5216
Treatment: Hard Coat Annodize

 

[jerryjerry05]

You should have a "pop up" type piston.
​I don't have much experience but I think Johnson used flat toppers???

 

[NEKFORCE]

yes that 3029ps is a "POP UP" type.

 

[Nordin]

The 3029PS (old part number) and 3129PS (new part number) has a dome at piston top "POP UP typ".
They are both the right typ for your engine.

 

[jimmbo]

You should have a "pop up" type piston.
​I don't have much experience but I think Johnson used flat toppers???

Johnson used both type, the 'pop up' on cross flow engines, and the 'flat top' on loop charged engines, so did Evinrude, and Mercury.