140 Evinrude - broken piston ring, piston expansion?

[andys15]

Had a repeat problem the past two weeks, however, after each incident the engine ran fine once I reset the gap on the spark plug. In each case the spark plug electrode was smashed against the anode. At first I thought maybe a piece of whatever (reed valve, ring?) made it way in there and just happened to hit the plug. Seems unlikely being that the plug was struck again a second time. Highly unlikely a small piece of metal would hit the same spot before making it's way out the exhaust port. Compression isn't perfect, but not bad. 100/90/100/90. The problem cylinder is the top starboard cylinder, it reads 90 psi. I've heard this one also generally runs the hottest. I have a pickup on that cylinder and on the top cylinder on the other side. It seems to have been running slightly hotter this year, but nothing excessive or off the scale.<br /><br />Runs strong, idles fine.<br /><br />Both times this occurred it was at the end of the day, 4 pm roughly, heading back from fishing. The engine was cold (off for 3 hours each time). The trouble struck within a minute or so of running about 4000+ RPM. Is it possible there's some sort of rapid expansion that's going on that would cause the piston to hit the plug. I have spark plugs with a curved arm as the electrode rather than the flat type plugs. Not sure the numbers on either type, but I had the shop put the plugs in that are in there, and they said they're the right one's and I've been using them for years with no problems.<br /><br />Any ideas?

 

[R.Johnson]

Re: 140 Evinrude - broken piston ring, piston expansion?

You have a broken chunk of metal, or chunks' of metal coming from somewhere. My guess is you have a broken ring, and the piston is coming apart across the ring lands'.

 

[CATransplant]

Re: 140 Evinrude - broken piston ring, piston expansion?

Time to pull the head and have a look-see, before you get catastrophic engine damage, I'd say.

 

[Dhadley]

Re: 140 Evinrude - broken piston ring, piston expansion?

Which 140 do you have?<br /><br />What plugs are you running?

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

I'm going to pull the head and check it out. There may be a broken ring, but, I did put a flexible magnet in there and not chips or anything.<br /><br />The more I thing about it, I think it may be some sort of expansion anomoly, I hope anyway. Noth times I ran the boat I had no problems on the way out, however I have to idle for about a mile down river before I can throttle up. That may have allowed the engine warm slowly and evenly. If I don't see any problems I'm going to put those flat plugs in instead. I think I'll clean the water jackets up good too.

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

Originally posted by Dhadley:<br /> Which 140 do you have?<br /><br />What plugs are you running?

'86 Evinrude. Has a bubble on the back of the block. Not sure of the plug #, but the guy at the shop said they were a correct alternative. The other one's seemed to foul a lot. Anyway, I have standard looking plugs with an arm for an electrode rather than the flat plugs with just a center anode that discharges to the surrounding ring.

 

[Silvertip]

Re: 140 Evinrude - broken piston ring, piston expansion?

While possibly not the problem here, cold seizure is very possible. A piston heats up and expands more than a cool cylinder wall. Going "hammer down" on a cold engine rapidly raises piston temperature but the cylinder wall remains cool. If the piston to bore clearance closes up sufficiently (like to zero), cold seizure can occur. Perhaps thats what happened the first time and whats happening now is bits are coming off the previously damaged piston.

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

Originally posted by Upinsmoke:<br /> While possibly not the problem here, cold seizure is very possible. A piston heats up and expands more than a cool cylinder wall. Going "hammer down" on a cold engine rapidly raises piston temperature but the cylinder wall remains cool. If the piston to bore clearance closes up sufficiently (like to zero), cold seizure can occur. Perhaps thats what happened the first time and whats happening now is bits are coming off the previously damaged piston.

That's what I'm thinking. Hopefully there's no damage and it's only expanded enough to smack the spark plug. I'm still going to pull it apart. I'll check the exhaust port cover and see how the rings look from the side and if they rotate at all. Now I'm rethinking putting the flat plugs in. Better to hit to plug and effectively shut down the cylindr then to have an outright seizure.<br /><br />Also, I didn't note any damage to the piston head when I looked in the through the spark plug hole. Weird.<br /><br />The piston has that funky looking profile to it to where it slopes up in the middle to draw and scavenge the gases. That may be coming quite close to the plug.

 

[CATransplant]

Re: 140 Evinrude - broken piston ring, piston expansion?

You know, you still haven't told us what plug was in there. You're relying on the shop not making a mistake, yet they do.<br /><br />Get one and let us know the number on it. It could be as simple as the wrong plug in the engine. Not much clearance in there.

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

Originally posted by CATransplant:<br /> You know, you still haven't told us what plug was in there. You're relying on the shop not making a mistake, yet they do.<br /><br />Get one and let us know the number on it. It could be as simple as the wrong plug in the engine. Not much clearance in there.

Don't kow the plug #, I'm sitting at my desk at work. I'm sure shops do make mistakes. However, I've heard tell from others that the plug I have in there is an acceptable plug and it's used specifically because the others tend to foul. Also, even though I've replaced the plugs, it's the same model plug I've been using for 8 years.<br /><br />I appreciate the help though. I'll let you know what the plug number is when I check it tonight. Kind of weird I'd have this problem know after this much time.

 

[Blueclaw]

Re: 140 Evinrude - broken piston ring, piston expansion?

pull the head and check for play in the con rod.<br />Turn the piston to top dead center then turn a little past on the down stroke. see if the piston follows or lags. You can also take the handle of a hammer and press down on the piston to see if there is any movement up and down while turning the flywheel so the pistons on the down stroke and then pressing on the piston with the handle. It's okay to have some side to side slop but there should be no up and down slop. I've seen where the wrist pin was so sloppy it let the piston come up and wack the plug electrode

 

[R.Johnson]

Re: 140 Evinrude - broken piston ring, piston expansion?

That piston cannot expand, and hit the spark plug. It can come loose, and hit the plug. But you will know that by the sound. Plus! I don't think the engine will start again.

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

Ok, I pulled the head off and the side intake port cover. The top of the piston has a bunch of divits in it, mostly concentrated along the indraft side of the slope in the piston. I did find a small amount of small metal debris in cylinder. No scrapes on the cylinder wall, but the piston head has those little divots in it which are about 1 mm wide and about 3 mm long (same chuck of metal floating around?). Like I said, most of the divots were concentrated near the upslope of the intake side of the piston, which would suggest debris came in through the intake port. The intake port looked clean though. Also, with the intake port cover off I could inspect the side of the rings and they seemed ok. Didn't seem stuck and didn't rotate around the piston, so I'm concluding that I still have piston ring continuity all around (ie, they didn't break). The next step I guess is to pull the carbs and the reed box out and see if a reed valve broke? Any tests I can do before taking that route?

 

[Walker]

Re: 140 Evinrude - broken piston ring, piston expansion?

Time to split the cases and check the rod bearings, mainly on that particular piston.

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

Originally posted by Walker:<br /> Time to split the cases and check the rod bearings, mainly on that particular piston.

Didn't feel any slop in the piston up and down. I'll check it close once I have it apart to check the reedbox. Doesn't sound like a piston ring problem though, right? I didn't see any scarring or gauling on the cylinder wall.

 

[Walker]

Re: 140 Evinrude - broken piston ring, piston expansion?

Although I can't see your cylinder and piston it does sound like something entered the combustion chamber through the intake port.

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

Originally posted by Walker:<br /> Although I can't see your cylinder and piston it does sound like something entered the combustion chamber through the intake port.

Sounds right to me. Now whether it was part of a reed or a main bearing breaking up I'm not sure. Like I said, I haven't seen anything else to indicate that there was any kind of failures anywhere else (reed or bearing). Could be just a stray piece of debris. I've torn these engines apart before and rebuild, it's just not something I'm into doing right in the middle of the season, epecially when it's not obvious that there's anything wrong with it per se. 4 years ago I had another 140 (1977) that had an oversized prop on it (another one of those "the shop said it was ok"). Anyway, it wound up breaking the crankshaft. It ran for 2 years with a broken crank (minor slop in the flywheel). At the end of the last season with that engine I ran it faster than normal on the way in one the final trip and the damage was final, yet it still ran enough to get in. The crank had enough slp and stress under heavy load to finally gouge the race which essentially killed the crankcase intake pressure (disrupting the whole two cycle process for two cylinder out of four). Wound up needing a new block so I just sourced out the engne I have now for $1,500. Those engines are pretty amazing though.

 

[Blueclaw]

Re: 140 Evinrude - broken piston ring, piston expansion?

might have gulped a reed. that would be the next look.<br /><br />what did the ports look like on that cylinder?

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

Originally posted by Blueclaw:<br /> might have gulped a reed. that would be the next look.<br /><br />what did the ports look like on that cylinder?

The ports looked ok, but the intake side of the upslope on the piston head had a concentration of divots, as if it was sandblasted by something coming in the intake port.

 

[andys15]

Re: 140 Evinrude - broken piston ring, piston expansion?

One quick question, from what I remember seeing the last time I had one of these opened up it looked like each crank side of the crankcase was it's on seperate chamber serving one cylinder. Am I correct in assuming this. It would make sense if they were, other wise you'd get irregular mixture pressure into the cylinder on intake. I'm wondering this because if it was a reedvalve failure, then it could explain debris on only one cylinder, instead of possibly more than one cylinder. BTW, thanks for the responses.