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1987 4.3 L Merc vibration

I have a 1987 Mercruiser 4.3 and it vibrates at around 2400 rpm in gear and at about 2200 rpm in neutral. It shakes the dash board if I hold it to that speed. It clears up at lower and higher rpms. Is this typical of a Merc without the balance shaft?
 
Re: 4.3 Merc vibration

I figured I eliminated the prop and lower gears since it still vibrates in neutral. I guess we'll see how the U-joints are when it comes out for the season in a few weeks. You don't notice the vibration looking or touching the engine, it's just the resonance through the boat that's noticeable.
 
Re: 4.3 Merc vibration

I could be mistaken but I believe that the early v6 gm motors were not counterbalanced.

If someone know for sure please chime in.

I think 1988-1989 was when they came out with the counterbalanced V6



Was this issue present since new or something new???
 
Re: 4.3 Merc vibration

I've only owned the boat since last year so I have no other experience with it. I read about a "balance shaft" that was installed, I thought starting in the 90s.
 
..."I think 1988-1989 was when they came out with the counterbalanced V6"

I believe that is correct. Also, the earlier V-6s were not firing motors. The 4.3 V-6s have the splayed rod journals that make them even firing.

Jeff
 
The early GM 4.3s that don't have the balance shaft aren't as smooth as the later ones that do, or the V8s but shouldn't shake the dashboard. It a slight resonance you can feel if you are sensitive to mechanical things but not at the level you describe. I'd check the ignition system first to make sure its really firing on all 6 cyls.
I have a 1988 and the resonance is something no one but me would notice.
 
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