1998 Force 120 quit today

hello

My motor has been working fine for a while now. Today it nearly stranded me for the first time.

I ran the motor for about 15 minutes at full throttle getting across the lake. On the return trip, it ran for about 5 minutes then I heard the RPMs dropping then confirmed that on the tachometer. It took about 10-15 seconds to go from 4200RPM to 0. Then it wouldn't start or even try to turn over.

After venting a few colorful metaphors I dropped the trolling motor and planned to go as far as that battery would take me before pulling out the paddle or trying to call for a tow.

After about 5 minutes of fuming, I asked my wife to turn the key to see if it would try to start. After a couple of attempts, it did. However, it was a VERY rough idle and it would only hold that at about 1/2 throttle. So we putted close to the marina. Then i went full throttle (since we were close) to see what it would do. It was still a rough run, but it managed about 20mph. Once in the marina it died because it couldn't go down to normal idle (for the no wake zone). Loading it on the trailer was "fun".

Any ideas? This was sudden and without warning. I appreciate your help.

Re: 1998 Force 120 quit today

Check the compression on all four cylinders. What you have described sounds a lot like one or two bad pistons.

Re: 1998 Force 120 quit today

oh that would hurt my feelings SOOO badly! This motor was rebuilt top to bottom October 2007. 4 new pistons were part of the mix.

Thanks for the tip. I'll check.

Re: 1998 Force 120 quit today

I had a similiar incident with my 1989 force 125hp. It turned out the the woodruff key under the stator broke. I put in a new woodruff key and I was good to go.

Re: 1998 Force 120 quit today

Doh, forced to show how naive I am with outboard anatomy... what is a woodruff key? I pulled out the Clymer manual to locate it, but could not. Is it related to the trigger?

Going to check compression now. Thanks.

Re: 1998 Force 120 quit today

Spinkick said:

Doh, forced to show how naive I am with outboard anatomy... what is a woodruff key? I pulled out the Clymer manual to locate it, but could not. Is it related to the trigger?

Going to check compression now. Thanks.

Click to expand...

It is under the flywheel it is the key that hold the fly wheel to the shaft so it hold the timing good luck

Re: 1998 Force 120 quit today

Thanks for the info.

Much to my misfortune, Frank is apparently correct... #2 piston is history. The loose metal was "plugged" at the plug hole until i knocked it out.



How in the world can one piston overheat and cause damage like this and the other 3 work fine? 1998 Force 120 for sale - as is

Re: 1998 Force 120 quit today

Spinkick said:

How in the world can one piston overheat and cause damage like this and the other 3 work fine? 1998 Force 120 for sale - as is

Click to expand...

Answer: Plugged carburetor jet. She ran lean in that cylinder.

Re: 1998 Force 120 quit today

Boy thats a shame.When you get it setup again frequently check the condition of the plugs until you are sure shes not lean.

Re: 1998 Force 120 quit today

Sorry to have been correct! That is piston damage due to detonation, due to a lean run. It is very typical for only one piston of a pair to be damaged when only one carb runs lean.

Admittedly, I can not see too much in the photo supplied, BUT I do believe you have a little aluminum throw-off stuck to the bore, and very light scoring. I do not see any deep scoring that would require disassembling the engine for boring. It may be possible to repair with the engine still on the boat.

SO: The good news is that it MAY be possible to replace just the one damaged piston without disassembling the engine. Since a shorted plug will not fire and the cylinder is now dead, it can no longer detonate. The thrown off aluminum may have shorted the plug early, preventing major scoring to the cylinder wall.

Remove the carb and manifold. Remove the rod big end capscrews. Push out the piston. Examine the bore closely to assess the scoring damage. If mild: Scrape off any thrown off aluminum by hand, then lightly hone the bore. Replace the piston with the same sized one.

If you are mechanically inclined, total time will be 3-4 hours if you have never done it before. Total cost about 125 for Wiseco piston, rings, and bearing kit. I recommend Wiseco because they are easier to install without special tools. Stock pistons need a spacer and a press to install on the rod. Unless damaged, the head gasket will be re-useable.

Do not sell the engine because of this. You will take a major and unnecessary loss. When you repair it, As I repeat and repeat over and over again, ad infinitum, ad nauseum--Am I being redundant?

ALWAYS--ALWAYS--ALWAYS install a cheap 3 buck filter between the fuel pump and carbs. Most times lean runs on one carb are due to a chunk of something that has passed the fuel pump and clogged the inlet needle of one carb.

Re: 1998 Force 120 quit today

Thanks Frank... that's some serious detail. I am mechanically inclined, but may be short on some of the tools. But you can bet if I take to someone that does have the tools, I'll be speaking your language!

As for the filter, I do have a filter betweent the pump and carbs. In addition, after the rebuild I put a 10-micron water separator filter on it as well. It's a bummer that something got through.

If it is running lean will the plugs have a dry "burnt" look? About 2-3 months ago I checked compression (ended up being a bad battery). At that time the plugs all were a bit oily, but otherwise no deformities. All plugs today were a bit dry and "burnt", but most of the material wiped off.

I have been religious about the 16oz oil to 6 gallons gas as recommended, so hopefully that is not a factor.

If there is a jet clogged, will it require a carb rebuild? That's something I've never done auto or marine.

Thanks so much.