Replacing piston in Force 125 question?

[SmurfOnAScarab]

I was reading through the force forums, and found this thread http://forums.iboats.com/showthread.php?t=266436&highlight=125

I was just wondering if I can follow the procedure to replace a piston in a 89' Force 125.

I have 125PSI compression in cylinders 1, 3 & 4. About 55-60PSI in #2, I pulled the head, and the piston is badly destroyed, kind of like someone before me put the wrong plugs in it, and it broke the grounding strap off and was dinging around in the cylinder. I am hoping this will help bump compression a little.

The boat has trouble idling. It will fast idle with no problems, but normal idle it wont stay running very long, and ALWAYS stalls when engaging the drive. Higher throttle and WOT no problems, the boat runs about 28-29mph. (1989 Bayliner 1902 Capri Cuddy)

Thanks for the help!

 

[Frank Acampora]

Re: Replacing piston in Force 125 question?

From your description, what you had happen is detonation as a result of one carb running lean. If the cylinder walls are not scored, you can replace a piston without disassembling the engine. If the piston is damaged as badly as you describe, it is likely that the cylinder walls are scored. Scored cylinders REQUIRE disassembly and overboring.

However, it will take a bit longer to replace a single piston with the engine still assembled, on the four cylinder engine because the reed openings are vertical, making it more difficult to get at the big end of the rod.

You will also need to check the reed blocks to be certain that the engine did not eat a reed retaining screw. While you have them out, tighten all the reed retaining screws and the reed block (flat head) retaining screws. Better yet, remove them and reinstall with thread locking compound.

Be absolutely certain to disassemble and clean the carbs to be sure a lean run was not caused by some junk in one. When you re-set the carbs, do not go leaner than 3/4 to 1 turn out from lightly seated on the low speed adjusting needles. Too lean gives a beautiful idle but melts pistons.

To avoid junk in the carbs, put a cheap plastic disposable in line fuel filter between the fuel pump and carbs.

 

[SmurfOnAScarab]

Re: Replacing piston in Force 125 question?

I removed the piston in just about a half hour. No problems really, have all 16
roller bearings, and everything else is accounted for.

The pistons damage definitely isnt detonation, some piece of metal was in the
cylinder. The walls, however are not scored, I did a nice hone job on it, put a
bore gauge in there to check things out, and we are good to go.

The piston did not eat a reed retaining screw, at least on cylinders 1 or 2. As
there is no damage in 3 or 4 and good compression, I will say its ok, but since
I have the gasket kit, I am going to pull them and just make sure they are
tight.

The carbs were definitely not running lean, I rebuilt and synch'd them myself.
(I am an Master ASE auto technician, and have quite a bit of marine experience), I am just not familiar with many outboards.

overall the job was rather easy. It is dark out now, and I am going to wait until tuesday night to reassemble the engine.

Frank, I have read through the forums and your posts and threads are most helpful.

Thanks for all the input!

 

[SmurfOnAScarab]

Re: Replacing piston in Force 125 question?

 

[SmurfOnAScarab]

Re: Replacing piston in Force 125 question?

Well successfully reinstalled the piston last night. It got dark fast, and I had a late start, so all I accomplished was to install the piston.

Use transgel to hold the races (cages) in places on the rod and cap, and to hold all rollers in place, had no problems what so ever. The piston went in nice and smooth, and the cap installed fairly easy after figuring out the right tools to use to get it in place. All tightened up to 170in-lbs, and then I called it a night. Tonight I will be putting the rest of the motor back together, and doing a compression test, then firing her up!!

I have pictures from last night, and will have more tonight after the engine is done.

Will post them up later!

 

[Frank Acampora]

Re: Replacing piston in Force 125 question?

Yep! She ate something alrght! Notice the two marks on the top edge of the piston on the exhaust side come up? That exhaust port is larger than the center ones. The top ring land was pushed up there. Probably on the downstroke and maybe by a busted ring which then entered the combustion chamber and rattled around a bit before leaving. Notice how angular some of the dents in the piston crown are? I can't tell from the piston photo-- Are all the pieces of ring accounted for?

I'm always open to better ways--What is Transgel? Is it a gasoline soluable adhesive to hold the rollers and cages? If so what national stores sell it?

 

[SmurfOnAScarab]

Re: Replacing piston in Force 125 question?

Yep! She ate something alrght! Notice the two marks on the top edge of the piston on the exhaust side come up? That exhaust port is larger than the center ones. The top ring land was pushed up there. Probably on the downstroke and maybe by a busted ring which then entered the combustion chamber and rattled around a bit before leaving. Notice how angular some of the dents in the piston crown are? I can't tell from the piston photo-- Are all the pieces of ring accounted for?

I'm always open to better ways--What is Transgel? Is it a gasoline soluable adhesive to hold the rollers and cages? If so what national stores sell it?

No all the pieces of the rings were not accounted for, after noticing that, my new look was the same as yours, pieces of ring went through there.

Transgel is for transmission assembly, its pretty much the same as vasoline. I have used it to assembly anything from a weedwhip to a 2000hp drag engine, to any type of marine engine.

Never have encountered a problem.

I use it for any engine or transmission assembly.

You should be able to get it at a good parts store (not like murrays or autozone, but a real parts store) or any tranny parts store should have it.

I use red for trans assembly and gold for engine assembly.