Hunter 34 1986, 3GMF Yanmar, Jumping around

[Beth and Bill]

We have been having vibration issues. We had her hauled out and replaced the shaft with new one, new coupling, new cutlass and had the prop reconditioned. The motor was realigned. The company doing the work has a great reputation and had reasons to do the needed repairs. The shaft was scored and bent from poor alignment. The engine had the fuel lines flushed and new filters 2 times in past 4 weeks plus a leaking fuel line was replaced. Problem: the engine still starts to jump when put in idle for a few minutes. I had the idle set up to where it needs to be and even tried idling up when waiting on a bridge. Of course it never happens when the mechanic is on board. I have faith in my mechanic. I grew up in a marina and have many certificates in marine engine repair; however that was a past life. Look at the attached video and please give any past experience you may have had like this.

 

[Charles Erwin]

Intermittent symptoms suggest mis fire so injector evaluation would be a worthwhile starting place. Why the fuel line ‘flush’? Which fuel lines and was there any trash in it/them?

 

[Beth and Bill]

The fuel line flushes because the boat was on the hard for a few years, and lacked proper care before hand. After first one, the filters loaded up. Have put about 21 hours on the engine from spring launch. So fuel clean all the time now. New purchase for us. Getting her back into good shape. Thanks for the reply

 

[Benny17441]

Basics, start at the motor mounts, inspect and test, not just visually, they all look good. If motor mounts are good it is a mechanical issue, valve lash, uneven compression among cylinders, fuel injectors...……… Also check fuel condition, was the tank also flushed?

 

[markwbird]

I have been dealing with a similar issue. In my case the problem occurred only in forward drive and only while the boat was moving. It turned out to be the clutch cone in the transmission. The intermittent slipping of the clutch cone will create a hammering vibration that is similar to what I see in your video. It may be that while in neutral you are still getting some intermittent engagement due a loose whatever in the tranny causing the tell tale hammering.

 

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[kloudie1]

Sounds like one cylinder is not firing .. Start with valve clearance then make sure the injectors are correctly bled then injector inspection.. Good luck with it..

 

[Gene S]

I have been dealing with a similar issue. In my case the problem occurred only in forward drive and only while the boat was moving. It turned out to be the clutch cone in the transmission. The intermittent slipping of the clutch cone will create a hammering vibration that is similar to what I see in your video. It may be that while in neutral you are still getting some intermittent engagement due a loose whatever in the tranny causing the tell tale hammering.

I read that someone was having a similar problem and it was the cone clutch. How many hours since it was last lapped?

 

[Ken Cross]

What RPM does it idle at? Is this different when in forward or reverse, or just at idle in neutral?
If it does it in neutral, I'd suspect it's not the transmission, driveline, or prop related. More likely valves or injectors as Benny17441 suggested. Ours is rough at minimum idle, but if we bump it up to 900 or so until it gets warm, we don't notice roughness. We have a 2gm20f which is similar but only 2 cylinders.

Ken

 

[markwbird]

I misread your description. You say it happens in idle not neutral. Are you saying this happens at idle while in gear? Does it happen in both forward and reverse? My guess is that it happens in forward gear only. If so, I bet it’s the drive cone.

 

[Beth and Bill]

The cone in the clutch fixed the issue. Many thanks for all who suggested it. It help me get it fixed ASAP. Back sailing!

 

[datasailor2]

Ditto, Engine was jumping and banging infrequently/intermittently at first and more often as time passed. Looked and sounded like there was a problem with engine, shaft balance, or bending. When I realized the issue only happened in forward gear it dawned that tranny was more likely the issue. I pulled Tranny (not easy task), took it to qualified shop, and presto the mechanic explained the Cone gear design and that it was worn causing the tranny to repeatedly engage and slip, which in turn caused the engine to jerk about like crazy (sort of like dropping the clutch hard on standard auto tranny). Now the question is (and there is a lot of opinions), is there something about how the tranny is set while sailing with and without the engine running that might cause premature wear on cone gear?