2000 Mercruiser 4.3 Alpha In Gear = Bumping from behind engine
 

Hi! My first post has to be a sad one... Just bought an 18 ft shabah (2000) and I LOVE it! BUT


2000 Shabah 18

Mercruiser V6 4.3 Alpha drive

Thunderbolt V (2 barrel carb)



When in Gear: I hear a loud bumping at every revolution of the crank/ drive shaft?

• The sound is beind the engine
• Sound is not as loud behind boat (compared to inside of engine compartment)
• The sound DOES NOT occur when in neutral (revving to any RPM)
• The sound gets faster when in gear & throttle is increased(although it is harder to tell because engine drowns it & it gets too fast to tell)

HERE IS VIDEO/AUDIO OF THE SOUND (Engine in gear @ ~ 2000 RPM?)
http://www.youtube.com/watch?v=whqcE6xMZS8

Re: 2000 Mercruiser 4.3 Alpha In Gear = Bumping from behind engine
 

It should be noted that there was an issue with the prop when I bought the boat: 4 blade 21P had a large chip on one of the blades... Should have known

Re: 2000 Mercruiser 4.3 Alpha In Gear = Bumping from behind engine
 

It sounds like you have a bent prop shaft likely from a prop impact. Take it into a Mercruiser repair facility & have them check it out before you do some serious damage.

Just curious though, didn't you put the boat in the water & take it for a test run before buying it?

Re: 2000 Mercruiser 4.3 Alpha In Gear = Bumping from behind engine
 

Yes. I heard a slight knocking, but it actually runs very well. The sound seems to have gotten worse. The prop shaft is in the lower unit. Sound seems to stem from directly behind the engine.

Re: 2000 Mercruiser 4.3 Alpha In Gear = Bumping from behind engine
 

Prop shaft, drive shaft or coupler. Take your pick. Either way it needs to be repaired asap.

Re: 2000 Mercruiser 4.3 Alpha In Gear = Bumping from behind engine
 

Prop shaft is solid. U joints solid.

Used a wooden dowel to listen for source of issue. Lower unit...

Turns out I left the rubber grommet in the old prop when i put on the new one. Prop was shaking all over the place :shakehead:

I am a new to boating. I was hoping I wouldn't make these mistakes, but I figure they are inevitable. Glad I got down to it asap

Thanks for advice

Re: 2000 Mercruiser 4.3 Alpha In Gear = Bumping from behind engine
 

You didn't mention that you had already replaced the damaged prop that came with the boat. No worries about making 'mistakes' cuz we all do it. Glad to hear it was a simple problem and easily remedied.