Engine clicking/knocking until spark plug boot removed

[rd1002]

When we were going to take our 1985 Sea swirl 6 cylinder boat out yesterday from the time we turned it on we heard a clicking /knocking sound that was new. We were already out on the water but we didnt go out long and it actually seemed to run fine. The noise did not get any louder or anything. When we were back home we found that when we take off one spark plug boot on the one closest to the back of the boat on the driver side it totally goes away. We did have someone check the compression in the cylinders and they are all good. Also the temperature was never high and the oil is all good. Could it be like a bad spark plug wire making it make that sound? Or what might it be. Just would like to know maybe the order of things to look at if anyone knows. Thank you.

 

[Ibl0wstuffup]

Run it in the dark and spray the wire with a squirt bottle. Look for electrical arcs. An arcing wire can make noise, but it's more of a snapping sound. If it's not arcing, check for a cracked plug. Might want to put a vacuum guage on it too.

After that I would do a compression test with a warm and cold engine. If that doesn't tell you anything then I would leak down test that cylinder.

I would also pull the valve cover and take a look under there.

 

[Idlespeedonly]

Depending on what you classify clicking or knocking, it could very well be a rod bearing.
Did it sound like it was coming from the lower area?
Since you said it ran fine, a bad wire usually would cause a noticeable miss.

 

[Speak]

Depending on what you classify clicking or knocking, it could very well be a rod bearing.
Did it sound like it was coming from the lower area?
Since you said it ran fine, a bad wire usually would cause a noticeable miss.

Sounds like a rod knock. Removing the plug wire is common practice when diagnosing a rod knock. When you remove the spark you essentially remove the load off the piston/rod/bearing thus the knock goes away. Rod knocks can be heard really well when you snap the throttle open hard when in neutral from idle. The knock will disappear when the motor spools down with no load.

 

[rd1002]

It does sound like its coming from the under the valve cover I think. Rod knock is what a couple people suggested but would you be able still have the boat go out and drive normal like it did for us when we first noticed the noise? My husband is injured temporarily so I am trying to see what is involved in this without bothering him for now, and I appreciate any and all input. Please excuse my naivete I am learning as I go.

 

[Speak]

It does sound like its coming from the under the valve cover I think. Rod knock is what a couple people suggested but would you be able still have the boat go out and drive normal like it did for us when we first noticed the noise? My husband is injured temporarily so I am trying to see what is involved in this without bothering him for now, and I appreciate any and all input. Please excuse my naivete I am learning as I go.

The engine should perform still with a damaged rod bearing but not for long. Have it inspected by a mechanic. Don't want to see you in the middle of the bay with a seized engine.

 

[rd1002]

Thank you for all your input now again I am just learning. If it is a rod, can a rod be replaced without a huge deal? I have heard the term rod bearing and rod and lifter tap, are these all totally different things? Also someone said it could be a loose rod nut, has anyone heard of this? Thanks again.

 

[Bondo]

Thank you for all your input now again I am just learning. If it is a rod, can a rod be replaced without a huge deal? I have heard the term rod bearing and rod and lifter tap, are these all totally different things? Also someone said it could be a loose rod nut, has anyone heard of this? Thanks again.

Ayuh,... The connecting rod connects the piston to the crankshaft,...

A Rod Knock is a fatal flaw, in which a full on rebuild might fix,....

A lifter actuates the valves, 'n are somewhat serviceable in the motor, without a complete tear-down,....