Bad spark plugs caused this?

[Sailor Jerry]

I thought I would share my story about an episode I had recently. We travelled from homeport about 30 miles to our destination (another marina) without incident. When we were ready to leave the next morning we fueled up, and had difficulty starting the stbd engine. When it finally started it was vibrating and running rough. Upon getting out of the harbor, we could not get stbd engine over 500 rpms, and serious rough vibration. When I checked the engine compartment there was steam, exhaust gas and water spewing everywhere. Shut down the stbd engine, turned on the exhaust blower and returned to the marina we just left under the port engine alone. When the local mechanic diagnosed the problem, this is what he found: dirty spark plugs on the stbd engine caused the excessive vibration, which caused the stuffing box to leak and the port engine exhaust to come loose. Hence, the steam, water and exhaust gas. So, if you haven't checked your spark plugs in forever, you might want to.

[bud37]

Thanks for posting, you may not think so but I think you were lucky that happened when it did....kind of exposed a problem you had lurking with the exhaust hose, may have been installed wrong or as it goes people sit/stand on them compromising the clamping at the joint.Could have easily been at 4500 rpm out somewhere away from help.
Was the engine smooth the day before ?

[km1125]

Sounds pretty fishy to me. I'm assuming it ran OK on the way to the gas dock?

I do agree you got lucky on the exhaust though. The spark plugs didn't make that come loose, it was a problem waiting to happen. I'm also concerned about the stuffing box... well, not really the stuffing box but the engine mounts. If the engine was moving so much to affect the stuffing box, what do you think it's doing to the transmission gears and overall alignment with the shaft??

I could see A spark plug going bad but for several to go back and cause such a vibration issue would make me VERY suspicious.

On a related note though... I just ran into a spark plug problem with my dingy that plagued me for over a YEAR. The Cliff's Notes version: Would run great for 15-20 minutes flat out, then have trouble running. Let it sit for ~15 minutes and you could run again for about 15 minutes flat out, then it would have trouble. If you ran less than flat-out, it would run much longer before you had an issue. SOMETIMES would be VERY hard to start, other times would start right away. Looked at nearly EVERYTHING else, then finally decided to replace the single spark plug. Problem appears to be solved. I have never, ever, ever had such a weird spark plug problem. Yours could have been another.

[mjk1040]

I've seen in a vehicle brand new spark plugs not work before!

[Sailor Jerry]

Thanks for the feedback. I agree, the hose had a pre-existing problem. The mechanic showed me where the engine had overheated the hose sometime ago (before my ownership) and deformed the elbow. It really didn't take much for it to come a loose. It was fortunate that it happened just outside the harbor where it was easy to get back in. And, yes the engine sounded fine until we started up at the fuel dock. The mechanic checked the fuel/water separator first, thinking that was the problem. But nothing there. Water leakage at the stuffing box was not major. Just about a gallon an hour, a heavy drip.

[RGrew176]

It was good of you to share your experience. That is one of the great things about this and other boating forums. We share our experiences both good and bad and we all can learn from them. Hope you have no other issues.

[g36]

Yes I agree with Rgrew thank you for sharing

[dcrahn]

Misfire caused by the bad plug or plugs caused excessive vibration in the engine which in turn caused the already compromised exhaust hose to leak, as well as the stuffing box.