'97 Force 120 wont idle & banging/clunking sound

[xstoyz]

Hi All,

About a month ago while under way the boat stumbled a bit, and then after that it wouldn't idle without imediatly stalling. I have to keep it throttled up slightly for it to stay running. It makes a strange clunking/banging sound that is constant with engine speen but MUCh louder and more noticeable at low/almost stalling rpm. I am hoping I dont have a bad bearing.

I have checked compression and all seems good between 165 & 175. I put a inline spark tester on all plugs and they all had spark. All ths spark plugs looked fine, but i swapped them out with a known good spare set with no change.

If anyone has any ideas I would greatly appreciate your input. I am located in Tiverton RI if anyone is local and would be willing to come give their opinion that would be great!!


Thanks all,

Happy boating

Ed

 

[steelespike]

Re: '97 Force 120 wont idle & banging/clunking sound

Sure doesn't sound good no pun intended. Sounds like maybe a rod or some other internal part.You might try grounding one plug at a time see if it changes he sound.Inspect the crankcase carefully for damage.cracks bulges etc.Run it as little as possible I fear you have s a serious internal problem.

 

[xstoyz]

Re: '97 Force 120 wont idle & banging/clunking sound

steel,

thanks for responding. I am afraid of the same thing. Is there anything I can check to help determin what it might be? I have to run the boat about 3/4 of a mile sometime in the near future to drive it to the ramp to pull it out, other than that it is staying at the dock. I figured this would be easier to diagnose and work on in the water than on muffs. but now that it is getting cold out i need to get the boat out and set up for storage. I was hoping to have this problem fixed or at least pinpointed before putting it away I hate to put things like this off until spring.

Ed

 

[Frank Acampora]

Re: '97 Force 120 wont idle & banging/clunking sound

Dang! I hate to be the bearer of gloom and doom! Banging that remains with any engine RPM is usually indicative of a rod bearing having lost its rollers and this is the kiss of death for the engine because when that happens, the crankpin on that cylinder is destroyed. Usually, you will also see score marks and wear on the front half of the crankcase where the rod cap bolts rubbed against it.

This requires replacement of the whole crankshaft which is a very expensive repair. I have seen in previous posts a company that sells refurbished cranks for around 400-500 plus your old one--you don't want to know what a new one costs!

You can check for a bad rod bearing by removing the head and rotating the flywheel back and forth by hand. The piston with the bad bearing will have about 1/4 inch vertical play.

The other gloom and doom scenario is a broken crankshaft. Believe it or not, these engines have been known to run with a broken crank--not well, but running. That's something you would not expect at all. Again, rotating the crank by hand and watching the pistons will probably show the broken section.

At any rate, I would not run the engine at all until the exact problem is diagnosed. It could mean the difference between a repairable engine and a totally trashed one. If at all possible, get a kicker engine to get back to the dock or bum a tow.