I would appreciate any help that anyone could give me with an engine vibration/power problem that I have with my 1990 Hunter Vision. My boat has just been put back in the water and I have fired up the Yanmar 3GM30F. It works fine while in neutral and both idles well and runs smoothly up to 3700 rpm. However when I try to get up to cruising speed (6knots), I get black smoke out of the exhaust and I cannot get the engine above about 2700 rpm (Cruisng is at 3200rpm normally) I also get a tremendous vibration. The system seems to work well at slower speeds though. I have dived under the boat to check if there is a rope around the prop, but it is all clear. On going over the engine carefully, I did however find that one of the engine mounting bolts was loose and have tightened that. I still get the vibration. On checking the Hunter manual, I find that they recommend that the Prop shaft alignment be checked "regularily". The coupling, however is rusted solid and it looks like a daunting task to loosen it. Also the shaft looks alright and seems to run freely, although apparently it must be aligned to 3 thou, which you of course could not judge by eye. My question is really whether you all feel that shaft alignment is indeed my problem. Do you think I would be able to effect a major improvement in the vibration if I got to work on the coupling with some rust remover and a feeler gauge? Can anyone give me any advice as to techinque? The Yanmar people have given me another possible reason for the back smoke and inability to reach 3200 rpm. They feel it may be a constriction in the mixing elbow of the exhaust (coking up. Has anyone had a similar problem and found that it was the exhaust issue? Thank you for your input. I look forward to any words of wisdom you can offer. Richard
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I had a vibration problem . . .
I recently bought a 92' H28. It also had a vibration problem above about 1800RPM. While it was on the hard during the winter, I removed the coupling bolts and eye balled the alignment by rotating the shaft and looking for any gap between the coupling parts - look really good to me. Then a friend of mine said that you need to use feeler guages. When I probed with the feelers, it was obvious that the engine needed to be moved. Ended up doing about 5 turns on the front connectors and moved the front to port about 3/4"! You would think that you could see that by eye, but I couldn't. Once I got the engine aligned, I ran smoothly up to full throttle. There will always be "resonance" points where certian RPMs produce some vibration. The sweet spots on my boat are 2500, 3200 and 4000 RPM. I recommend you do an engine alignment if it hasn't been done in several years (or ever).
I recently bought a 92' H28. It also had a vibration problem above about 1800RPM. While it was on the hard during the winter, I removed the coupling bolts and eye balled the alignment by rotating the shaft and looking for any gap between the coupling parts - look really good to me. Then a friend of mine said that you need to use feeler guages. When I probed with the feelers, it was obvious that the engine needed to be moved. Ended up doing about 5 turns on the front connectors and moved the front to port about 3/4"! You would think that you could see that by eye, but I couldn't. Once I got the engine aligned, I ran smoothly up to full throttle. There will always be "resonance" points where certian RPMs produce some vibration. The sweet spots on my boat are 2500, 3200 and 4000 RPM. I recommend you do an engine alignment if it hasn't been done in several years (or ever).
New Zinc
I have the same engine. We got considerable vibration about 2500. This year I tried removing the shaft zinc and the vibration is about gone. Of course I need to replace it but would like to find one more balanced. Jeff
I have the same engine. We got considerable vibration about 2500. This year I tried removing the shaft zinc and the vibration is about gone. Of course I need to replace it but would like to find one more balanced. Jeff
Smoke?
If you have smoke when in gear, and vibration. And cannot get your RPM's up, then it could be the pitch of the prop. Did the prop get banged up during the off season? Goot chance it could be out of line, also. Those are the area the I (IMHO) would look at first.
If you have smoke when in gear, and vibration. And cannot get your RPM's up, then it could be the pitch of the prop. Did the prop get banged up during the off season? Goot chance it could be out of line, also. Those are the area the I (IMHO) would look at first.
Thanks Steve, Paul and Jeff
My prop does not seem to be damaged, I have just put on a new zinc, which is far less pitted and unbalanced than the old one, so I am going to try realigning the engine. I will let you know how that goes. Thanks for your help. Richard
My prop does not seem to be damaged, I have just put on a new zinc, which is far less pitted and unbalanced than the old one, so I am going to try realigning the engine. I will let you know how that goes. Thanks for your help. Richard
Mixing Elbow
Sounds like a fouled mixing elbow to me. I have had it happen to me a couple of times and always have the symptoms you describe. Archives have considerable discussions on this issue if you look under mixing elbow.
Sounds like a fouled mixing elbow to me. I have had it happen to me a couple of times and always have the symptoms you describe. Archives have considerable discussions on this issue if you look under mixing elbow.
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