Problem with #1 cylinder on 97 Force 120

[rmclaughlin78]

I am at a loss. Have had the powerhead rebuilt twice ($3400 for the first rebuild, second time under warranty) and same reoccurring problem. #1 cylinder burned through on exhaust side. Have had local shop check out problem, was charged over $700 and was told problem was fixed. Less than ten minutes in the water engine showed signs of overheat so we shut it down, pulled the head and the piston was burned through for the 3rd time. Also showed signs of weak water pressure and we have no thermostat installed. Of course, local shop won't stand behind their work and no one seems to have any idea why this is a reoccuring problem. Also reassuring, I have more knowledge of the Force repair manual than the mechanics that were working on the engine. Has anyone else run into this problem and if so, how have you solved it?

 

[pnwboat]

Re: Problem with #1 cylinder on 97 Force 120

I would say that you have a lean fuel condition. Most likely cause is the top carburetor. Sticky needle valve, float set too low, maybe even the fuel pump diaphragm needs to be replaced too. To be sure, I would go over both carbs and anything that is involved in supplying fuel to the carbs such as fuel lines, primer bulb, debris in the gas tank preventing proper fuel flow to the motor etc.

You should also be using surface gap spark plugs. NGK BUZHW or Champion 5898.

Weak water pressure is an indication that the water pump impeller needs to be replaced, or you have some blockage in the water passages in the block or lower end. You should also have a thermostat to control engine temperature. If you are removing the thermostat because it's running too hot, then you are not fixing the real cause for the problem, just applying a temporary "band aid" and there is a good chance that the real problem will come back and bite you.

 

[rmclaughlin78]

Re: Problem with #1 cylinder on 97 Force 120

After the first destroyed piston, we had the powerhead rebuilt. In addition, both carbs, upper and lower, were rebuilt, fuel system was flushed, all hoses on the engine were replaced, new waterpump assembly including housing and impeller were installed, cooling ports were blown with compressed air and had clean freshwater run through. First run after all the work and cylinder 1 was toast. Work was covered under warranty so we sent it back and they rebuilt the head for the second time. This time we had the local shop go over all of the work that had been done as we did not trust the original rebuilder. The local shop took the engine out and checked fuel and timing as well as the cooling system. They removed the thermostat and said that it would ensure that we don't overheat. Ten minutes into our run, we had steam out of the pee hole. Thank you for responding but I think we have tried just about everything and now we are dealing with a fried piston again. If you have any other thoughts i am all ears.

 

[pnwboat]

Re: Problem with #1 cylinder on 97 Force 120

What kind of boat do you have it on?

Carburetor running lean is probably the most common cause for the symptom that you are experiencing. Of course that's just my opinion, but others on this forum may have other thoughts.

I would suspect that someone has missed something. First place I would look is the carburetors. Float level and idle mixture. With the carburetor upside down, the float should be basically parallel to the carburetor body. Maybe just a smidgeon closer to the carburetor body. Idle mixture screw should be at least a minimum of 7/8 to 1 turn out from lightly seated. Anything less could cause a lean condition.

Second thing is timing. Factory manual states that 32 degrees before top dead center. Many folks set it to 30 degrees BTDC just to be safe.

Type of spark plugs. This particular motor requires surface gap plugs. Are you using standard automotive plugs that have the ground electrode on the side to adjust the gap. If so, they can cause a hot spot and burn a piston.

Any shop that says that they are removing the thermostat to insure you don't overheat would be one that I would shy away from. It certainly didn't work in your case. A water pressure gauge will verify that you are getting good water circulation.

I'm out of any ideas. Maybe someone else has some.

 

[rmclaughlin78]

Re: Problem with #1 cylinder on 97 Force 120

Thank you. We'll give your ideas a try!

 

[rmclaughlin78]

Re: Problem with #1 cylinder on 97 Force 120

To answer your question about the boat, it is a 16 foot Searay Bowrider. One other question...there are only two carbs on the engine, the top carb feeds cylinder 1 and 2 while the bottom feeds cylinder 3 and 4. If the carb is running lean, shouldn't be burning cylinder 2 as well? As of now, our only issue has been cylinder number 1. Again, thank you for your help, we are still looking into those other issues.

As an update, the local shop that we took the engine to for review said that we had a bad overheat sensor and that when the engine was reassembled the second time that the head gasket had been put on backward. These are the same guys that removed the thermostat. After verification that they did not find the problem, I removed the powerhead and disassembled it completely in order to replace the burned piston. I found that the old head gasket had not been put on improperly so they lied about that being the problem. I wonder what else they lied about. Fool me once...!