1992 Mercruiser 4.3 vibration under load at 1500 rpm

[dtag2308]

I have a 1992 Mercruiser 4.3 with alpha 1 gen II outdrive and 3 blade stainless prop. It has a vibration on slow acceleration from around 1500 to 1700 rpm's. It only happens when in gear and at slow acceleration. Any suggestions on where to start?? It also stalls when accelerating going in reverse. Any help will be greatly appreciated.

 

[havasuboatman]

Re: 1992 Mercruiser 4.3 vibration under load at 1500 rpm

Stalling going into reverse is most likely shift cable adjustment.
The vibration at low RPM I'd look first to the popeller. If the blades aren't true due to damage, or have been filed unevenly, or are bent. That will cause the vibration.
Also, run the boat on the hose adapter at idle and put the boat in gear. Check the prop nut for wobble and/or lateral (side to side) play.
If the prop is the culprit, replace it or have it professionally repaired.
If the prop shaft is wobbling, It needs to be replaced.

 

[steves937]

Re: 1992 Mercruiser 4.3 vibration under load at 1500 rpm

4.3l with out the balance shaft above the cam, have a balance issues around 1700 rpm

 

[JimmyOOOOO]

Re: 1992 Mercruiser 4.3 vibration under load at 1500 rpm

4.3l with out the balance shaft above the cam, have a balance issues around 1700 rpm

is it harmful to the motor?

 

[dtag2308]

Re: 1992 Mercruiser 4.3 vibration under load at 1500 rpm

Thank you for the replies....I checked the prop shaft with the dial gauge and found everything to be in spec with both straightness and bearing slop and everything was in tolerance. I was wondering if all the Marine 4.3's were balanced and apperantly they were not.....Thanks Steve for that info. What do I look for on the timing cover to tell the diference?

 

[steves937]

Re: 1992 Mercruiser 4.3 vibration under load at 1500 rpm

I think the 1996 4.3 and up have tha balance shaft, the shaft is driven by a series of gears instead of a timing chain, My Mercrusier shop manual is where i read about the vibration issue on the earlier 4.3 with out the balance shaft. I know there are some aviation engines that have warning placards on the panel stating to avoid prolong ops at certain rpms. So i will do the same.
My Starcraft has a 1988 4.3, i believe i can feel a little roughnes 15 to 17 hundred RPM but nothing shaking badly.
Your engine mounts might have sagged and caused some alignment issues which can lead to other drive issues, search aligment post.

 

[bruceb58]

Re: 1992 Mercruiser 4.3 vibration under load at 1500 rpm

If you have the original motor you more than likely don't have the balance shaft. Those engines came out in 92 and marine usually lags since they use up old stock first.