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Yet another problem in Cabo

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CaboJohn

Regular Contributor
My Overheat thread talks about the issues with my starboard engine and where we are (were) at. Now, I have developed a problem with the port engine...or perhaps the flex plate or transmission or ??. The boat is a 2002 Pursuit 3000 with twin 5.7 liter Crusader Captain's Choice and ZF Hurth transmissions.


Coming into port yesterday at idle we could hear a knocking sound. Checked it out at the dock today. It is the “good” port engine. All fluids looked fine so I started it up. The knocking (or tapping) sound is fairly loud and sounds like metal on metal. It only happens at idle and disappears about 900 rpm. It is irregular( tap, tap, tappity......tap, tappity, tappity....tap....tap, tap, tappity, tap......tap), about as fast as you might read that aloud. It sounds like it is coming from the rear and I think I can feel a little vibration on the gear case. It happens in neutral, and (as shown yesterday) when the boat is in gear and idling. Other than this the engine sounds fine (today) although I thought it might have been a little rough yesterday coming into the dock.


Before I do more tests or move the boat, I would very much appreciate opinions from those of you with more experience as to what I might be dealing with.


Thanks for your help.


CaboJohn
 
CaboJohn said:
............... about as fast as you might read that aloud. .............
Click to expand...
CaboJohn, would that be for the average reader, or one that just finished the Evelyn Woods reading dynamics course? :D

Bob's suggestion of a drive coupler damper spring may be a good one.
I too have heard these rattle or click at low rpm and then disappear above that rpm.
If so, it may not pose an immediate problem but will need to be corrected eventually.

The drive coupler would be similar to one of these.



18-5661_0.jpg


ALTDA-106A.jpg
 
Before ripping her apart, check to see if the engine is idling smoothly. If not, that alone will make that sound.

Jeff

PS: It is surprisingly difficult to get a really smooth idle in a marine engine with its ridgid motor mounts. Unlike a car/ truck application--where the motor rocks back and forth with a poor idle adjustment--a marine engine will stupidly sit there, taking it! A vacuum gage helps, BUT you can't use the convenient PCV valve hose from the carb as your vacuum source (as I once did. Doh! That changed the mixture soon as it's hitched up again.) You need to find a vacuum source, often difficult to locate, that can be taped into without changing the air/ fuel ratio the motor is getting.
 
2X on time to check the damper plate. Ideally, a little handheld borescope is the tool to check these out. You really don't want to defer this if the damper needs to be changed - just ask Knuckle what kind of havoc occurs when they cut loose. Alot easier to fix now, too, than after the parts start to separate.

Jeff: no mixture adjustment on a MPI setup.
 
Correct, I missed that, but that doesn't mean the motor is providing a smooth idle. Could be a bad injector(s) making a poor spray pattern and a rough idle, or ignition troubles. Either way, the motor doesn't rock back and forth like a car/ truck application, making it hard to tell.

I suggest a vacuum test to see if the motor is making reasonable vacuum at idle.

Jeff
 
Cabo John:

One of my twin crusaders (454, 350hp) ws making a similar tap/knock sound at idle but only in gear. My local mechanic suggested that if the idle is set too low they will make that noise in gear. I checked idle spped in gear and it was a bit low (about 400-500rpm). I adjusted it up slightly so that in gear it is more like 500-600 rpm and the knock went away. That was a few years back and I've had no isses since. Good luck.
 
Checked it out some more today. It rattles with no load at idle (750). It quits making noise at about 850-900. Unlike my previous report it does not rattle when in gear, even at idle. (I was confused over when it was in or out of gear when I heard it as we were first approaching the dock). The engine is running a little rough so it seems likely that is the issue, not the flex plate.

I pulled plugs (cold engine, before startup) which looked good other than #5 which was dry but somewhat red with some clear very small crystals around the rim. Tasted but it tasted like spark plug! I stuck a piece of 150lb mono with a loop on the end and swabbed the cylinder every which way. It came out dry and clean. I cleaned off the plug, then switched it with #3 plug which was clean with a nice tan. I will look at #5 again when motor cools down and see if crud comes back. We put 10 bottles of local fuel injector cleaner and gasoline conditioner in tank and fished for a few hours. Engine seemed better when we returned, but still some rattle at idle when out of gear.

It could be bad gas as we filled up prior to the problem. That tank was filled first so maybe the gas was "good" by the time they filled the second tank. Or it could be injector problems, or ???

Other than the annoying rattle (it actually sounds like a diesel) when approaching the dock, I did not notice any performance issues or roughness when underway.

Suggestions or ideas?

CaboJohn
 
@Rev Bob, Cheers? Doesn't sound cheerful to me! I take it you are not buying the theory put forward by several that a misfire at idle can cause such a noise. I questioned it at first, but the noise does go away when the engine smoothes out. I would think there would be some noise at no load even at higher RPM if it was a broken spring. But I am only speculating.

And, as an aside, I do wonder if the "engine running rough at idle causes the noise" theory is correct (and it must be in some cases as others have observed it), just what is it that is banging? It may in fact be the flex plate/hub assembly (when the engine misses, the hub and transmission shaft (unloaded) coasts ahead and hit some sort of stop between the splined hub and the flex plate itself). I actually cannot think of anything else in there that could make such a noise, and would make it go away when there is a load on the tranmission shaft. So even if a spring is not yet broken it could well be soon if I keep banging things.

CaboJohn
 
With out a doubt, a misfire in your engine will cause this noise. I would compression test #5. I would also cancel ignition on each cylinder with the trans in gear tied to the dock to see which hole, if any, is dead.
 
John,

You could have a rough port engine. We know the starboard engine needs some intensive care. You have described Metallic tap, tap, tap-pity sound from the bell housing, and you could feel it in the gear case. A loose, worn, or broken spring, on the damper plate will do the same, under light load, or no load. A low idle can make noise, an engine misfire.

I'll stick with damper plate inspection/replacement. You can probably get back to the slip under power with an engine miss, but if the damper plate fails (which is not uncommon), you can loose propulsion on that shaft.
 
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When I bought my boat I had the same noise and the surveyor said that the flex plate was starting to go. It only rattled at low idle just like you're describing. I found one cylinder on the cap was burned and the wire must have been arcing for a long time, probably years.

Replaced that three years ago and that was the last time it rattled. A LOT of flex plates get replaced for no reason so do that LAST :) Not to say they never fail....


Bob
 
Well, let me pile on here.... Reminds me of a joke I had heard when Yakoff Smirnoff was asked about what was different in the USA compared to Russia....He replied " warning shots". Our flex plate made no warning noise.

We were pulling away from the fuel dock and once in the open water area, throttled up to about 3/4 but when it hit just over 1500 rpm the flex plate exploded in (picture this) the rpms went up real quick to maybe 4500 in a split second with no load and then the engine locked. Remember at the time, we had NO CLUE what had happened other than a very frightening noise.

The plate, on its demise, had wedged itself in the bell housing and sliced the inside of it up beyond descriptive belief. If you saw 007 Goldfinger, it was like Oddjobs hat slicing thru the statue at the country club or the propeller of the airplane in the movie Con Air when the plane lands at the c a s i n o entrance in Las Vegas and slices right thru the plane.

Had that passed thru the bell house, it would have easily sliced right thru the bottom of the boat.

Marks borescope idea is a good one. The job was very simple and took LESS that 20 minutes to actually perform. It was the engine removal and replacement that took 2 days. If you can rule out an issue with the flex plate, terrific. I did need a new bellhousing but the entire job was just un-bolt and bolt back again. I think I used nothing more that an 11/16 socket for the whole thing
 
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