1992 ? Force 150hp Burnt Piston

[ddrieck]

Hello all,
I Just acquired what I believe is a 1992 50hp Force

Model: X1508F9A
S/N: x18853

It has a burnt number 3 piston with matching damage to the cylinder head. I am thinking about just putting in one new piston but anted to get a few opinions before I start.

- Is it worth the effort and expense to repair this outboard
- Were these outboards prone to this kind of damage?
- Does this look more like detonation due to improper timing as apposed to a lack of lubrication. The other 4 pistons look to be in great shape.

 

[pnwboat]

Re: 1992 ? Force 150hp Burnt Piston

- Is it worth the effort and expense to repair this outboard
If you are mechanically inclined and are willing to do the work yourself, you could probably build a case to say that it is worth it. Replacement parts are relatively cheap, but only available on-line. These motors are a basic old school 2-stroke design. Nothing very fancy.

- Were these outboards prone to this kind of damage?
They're not any more susceptible to this kind of damage than other 2-stokes of that era. Some of the newer computer controlled motors may have fail safe measures that will help to minimize out of spec. operation, but you really pay a lot for it.

- Does this look more like detonation due to improper timing as apposed to a lack of lubrication. The other 4 pistons look to be in great shape.
Looks like either ignition timing to far advanced, or fuel mixture too lean. What ever reason, it has generated so much heat that it partially melted the piston.

 

[Frank Acampora]

Re: 1992 ? Force 150hp Burnt Piston

What you have is detonation damage due to the center carb running too lean.

If the cylinder walls are not scored, you can replace that one piston without disassembling the engine. Simply remove the carb and manifold, reach in and unbolt the red cap screws and push out the old piston and rod assembly. Do not lose any of the 16 rollers on the rod big end.

Check the setting on the center carb, clean it and reset. That carb only services one cylinder so it is jetted differently and since less airflow goes through it, it is easier to run it too lean.

 

[moparman]

Re: 1992 ? Force 150hp Burnt Piston

two questions, is there another number after the 9 in the model numbers,and is this a 150 hp instead of50hp?

 

[CharlieB]

Re: 1992 ? Force 150hp Burnt Piston

Force ran 30 HP per cyl

5 X 30 = 150

Double check your model #, I think you may have switched a couple of character around, more likely may be 150F89A

The major change in the model years are which ignition is installed.

 

[Force 120]

Re: 1992 ? Force 150hp Burnt Piston

Hi,
Check out my post
http://forums.iboats.com/showthread.php?t=338482
My motor had the same problem as your.
I put a good used piston on it and honed the cylinder a bit. Put it back and got it run good now.

 

[ddrieck]

Re: 1992 ? Force 150hp Burnt Piston

Model number is posted correctly.

Its definitely A 5 cylinder 150hp outboard.

I figured the center carb feeds only the number three cylinder and that it was more than likely running lean. The cylinder wall looks good and shows no signs of scoring at all

Sounds like I can fix this old outboard fairly easily if I can get my big hands in there to work on it. Could changing the piston be done with the outboard still hanging on the boat? This thing is huge and it would take 3 men and a small boy to get it off

Also, the head is pretty banged up as well. I have run 2 stroke snowmachines in the past with the same sort of head damage with little or no ill affects.

 

[pnwboat]

Re: 1992 ? Force 150hp Burnt Piston

If area around the center carb is free from obstructions, yes it can be done while still on the boat. You need to remove the carb(s), adapter plate, and reed block assy. That will expose the interior of the block and you can access the connecting rod bolts for that cylinder. There are 16 loose connecting rod roller bearings that will fall out when you remove the rod cap. Don't drop any into the crankcase. Pay close attention to the rod cap. It's made to only go on one way.

 

[ddrieck]

Re: 1992 ? Force 150hp Burnt Piston

Any suggestions on how to keep the the roller bearings from dropping? Magnet, stuff full of rags....?

Anyone know what the stock standard piston size is for this 150?

 

[pnwboat]

Re: 1992 ? Force 150hp Burnt Piston

Rags are best. You want to avoid using a magnet on the bearings if possible as this can magnetize them and cause them to attract metal particles. Not something that you really want them to do. When reassembling, use grease to hold them in place.

 

[Force 120]

Re: 1992 ? Force 150hp Burnt Piston

After 1991, The piston size is 3.375" stock size. You can find a good used piston other motor or buy a new one from iboats.
Make sure you have 1/4" or 3/8" Square Drive Socket 12-Point Std, 1/4" Size socket to remove the cap bolts. Need a small hand to install all the roller bearing back.

 

[ddrieck]

Re: 1992 ? Force 150hp Burnt Piston

Thanks for all the advise and I am glad I asked. Looks like this outboard that I was ready to write off is acutually worth fixing without spending a grand.

I see iboats has the pistons but no head gaskets. Can someone point me in the right direction for the gaskets. I would rather not visit a local dealer.

 

[Frank Acampora]

Re: 1992 ? Force 150hp Burnt Piston

Unless the head gasket is actually damaged, re-use it. It will torque right down and will not need to be re-torqued after running the first time. I always re-use head gaskets on my Force and chrysler engines for my personal use. However, when rebuilding for another person, I always use a new one--avoids the appearance of shoddy workmanship.

Torque the head bolts to 225 INCH pounds in a spiral pattern starting at the center of the head. Do it in two or three steps: example 125, 175, 225.

Once you find the bore size ie. either 3.3125 or 3.375 send me a private message. I may be able to hook you up with a good used piston.

 

[ddrieck]

Re: 1992 ? Force 150hp Burnt Piston

PM Sent