4.3L Puzzle

[Capt. T]

I have a 18' Rinker with 4.3L Vortec Mercruiser. Through stupidity I froze it a couple years back and had to have it rebuilt (new block etc.) Anyway, by last summer though I had it sorted out and running - wrong answer!<br /><br />I had a full crew aboard and the engine was working hard to plane us out when I heard a loud metallic bang. IMHO not from hitting anything, sounded like metal breaking. Engine lost power, stated missing but never stopped running. I pulled throttle back and putt-putted back to dock.<br /><br />I checked everything, didn't see anything obvious so I took it for a test. Got up and on plane just fine, made it 3/4 round the bay and starts missing. Putt-putted back to dock, put it on trailer and gave to the marina.<br /><br />They said they ran it for two hours in the tank and ran fine, found nothing wrong.<br /><br />Any ideas BEFORE I put it back in the water and have to get a tow back to the landing?<br /><br />Thanks in advance!

 

[DJP]

Re: 4.3L Puzzle

Can you identify the "missing" as an engine mechanical problem or does the vessel just seem to lose power in the water while underway. Can the "missing" actually be slipping ? Or is there a definite mechanical noise associated with the missing every time the vessel does this ?

 

[DJP]

Re: 4.3L Puzzle

Kinda sounds to me like a spun coupler, if in fact the motor runs and runs well and the noise only happens upon power failure. Thus the fact that the marina could run your vessel without a load on it. Preventing the coupler from not sustaining a load might cause your vessel to act in such a way.<br /><br />

 

[Capt. T]

Re: 4.3L Puzzle

No new or additional mechanical noises the second time around. Just missing, running very rough and loss of power.<br /><br />I like the spun coupler idea.

 

[DJ]

Re: 4.3L Puzzle

Cap't,<br /><br />The coupler could have been your noise. But, a couple won't make the engine miss.

 

[DJP]

Re: 4.3L Puzzle

True a coupler will not make an engine miss, clarification please... Do you experience a loss of power whereby the engine misses, like in not firing on all 6 cylinders, or just slipping like you're experiencing cavitation.

 

[johnkc]

Re: 4.3L Puzzle

your loud metalic bang sounds like the clutch dog in the lower unit jumped .when they jump under that type of load you swear you may have hit something.and once a clutch has jumped once it will never hold ,it will continually get worse/more frequent.with coupler splines failure you will have metal shavings at the drive shaft where it enters the coupler and the boat will not move.if the rubber let loose to the splined core or outer hsg you will have possibly smelled burnt rubber and you should be able to see bits of rubber on the drive shaft as it enters the coupler and the boat may only be able to idle around in gear.

 

[DJP]

Re: 4.3L Puzzle

I agree, unless the entire rubber boot separated from the spline housing, thus creating a "freewheeling" spline and boot, which under normal conditions would adhere to one another because of the inertia exerted upon same. Up to the point at which the inertia is circumvent to the opposing force of the propeller motion pushing against it, causing the boot to again seperate and cause a "cavitation" effect within said vessel. Giving the apperance that in fact the engine had lost power when in fact the drive train lost torque caused by lack of friction within the spline boot assembly.

 

[Capt. T]

Re: 4.3L Puzzle

Definitely a loss of power from the engine. However, excessive torque load etc. could be causing the engine to misfire etc.

 

[flashback]

Re: 4.3L Puzzle

 

[DJP]

Re: 4.3L Puzzle

No duh, it was just an analogy, but I'll change it for continuity sake. Thanks.