I recently bought a hunter 30 and had the engine serviced. The boat shakes rattles and rolls at certain rpms when in gear. Mechanic says it is common to the hunter 30 and not the cutless bearing. It just doesn't sound right. Any advise?
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Check your rpm.
many of these 2-3 cylinder engines act like they want to shake themselves to death at too low of an rpm. Check the specs for your engine. Mine 3GM30F needs to be about 900 rpm to keep it from doing this. Good Luck Dwain 98 H340
many of these 2-3 cylinder engines act like they want to shake themselves to death at too low of an rpm. Check the specs for your engine. Mine 3GM30F needs to be about 900 rpm to keep it from doing this. Good Luck Dwain 98 H340
kind of normal....on some boats
most diesels have certain rpms that they shake more at than others...as well as harmonics of the rpms however, you could have something wrong that may exsasperate the problem, such as: a bad motor mount, a bent prop shaft, a bad cutlass bearing, a bent or out of balance prop, It could simply be barnacles on the prop. One cylinder engines are the shakiest of all. Also check engine alignment and the tightness of the motor mounts. Good luck.
most diesels have certain rpms that they shake more at than others...as well as harmonics of the rpms however, you could have something wrong that may exsasperate the problem, such as: a bad motor mount, a bent prop shaft, a bad cutlass bearing, a bent or out of balance prop, It could simply be barnacles on the prop. One cylinder engines are the shakiest of all. Also check engine alignment and the tightness of the motor mounts. Good luck.
You can...
do a quick check of the cutless bearing yourself by trying to move the shaft, where it goes through, up/down...side to side. It should have very little play in it, either direction, 1/16-1/8" max. A better guess would be motor mounts if they are originals and/or more than 10 years old. As Dwain said, all diesels have a 2-3 rpm levels they "don't like", but you should be able to find broad ranges where thing are pretty smooth. Has the engine been aligned in the past 5 years?
do a quick check of the cutless bearing yourself by trying to move the shaft, where it goes through, up/down...side to side. It should have very little play in it, either direction, 1/16-1/8" max. A better guess would be motor mounts if they are originals and/or more than 10 years old. As Dwain said, all diesels have a 2-3 rpm levels they "don't like", but you should be able to find broad ranges where thing are pretty smooth. Has the engine been aligned in the past 5 years?
Thanks guys
Diver scrapped the bottom last week and two new motor mounts put in last year. This 2 cyl engine runs rough at low idle speed and then again at a higher rpm (very smooth running in between). I intend to have the bottom redone and I will check the cutless bearing at that time. I'm not sure how many blades are on the prop, will that make a difference three vs two? My mechanic is pretty good at what he does and he believes it is the water turbulence created from the prop against the hull that is making the rough sounds.
Diver scrapped the bottom last week and two new motor mounts put in last year. This 2 cyl engine runs rough at low idle speed and then again at a higher rpm (very smooth running in between). I intend to have the bottom redone and I will check the cutless bearing at that time. I'm not sure how many blades are on the prop, will that make a difference three vs two? My mechanic is pretty good at what he does and he believes it is the water turbulence created from the prop against the hull that is making the rough sounds.
Rudder Post
On my 1983 27', the top of the rudder post is worn. At certain rpms turbulence vibrates the rudder. The post banging the top guide sounds like you're about to come apart. Put your foot on it and it stops. Bill
On my 1983 27', the top of the rudder post is worn. At certain rpms turbulence vibrates the rudder. The post banging the top guide sounds like you're about to come apart. Put your foot on it and it stops. Bill
Natural Frequency and Resonance
"Natural Frequency Frequency at which a mechanical system will vibrate freely. A pendulum, for example, always oscillates at the same frequency when set in motion. More complicated systems, such as bridges, also vibrate with a fixed natural frequency. If a varying force with a frequency equal to the natural frequency is applied to such an object the vibrations can become violent, a phenomenon known as resonance. " I believe all boats will experience this. You run the motor at just the right frequency, it will vibrate rather violently. Decrease or increase the rpm a notch, the vibration will disappear. For some boats, this natural frequency will be far below or far above the normal rpm range of their motor. I wouldn't worry about it except to avoid running the motor at this rpm.
"Natural Frequency Frequency at which a mechanical system will vibrate freely. A pendulum, for example, always oscillates at the same frequency when set in motion. More complicated systems, such as bridges, also vibrate with a fixed natural frequency. If a varying force with a frequency equal to the natural frequency is applied to such an object the vibrations can become violent, a phenomenon known as resonance. " I believe all boats will experience this. You run the motor at just the right frequency, it will vibrate rather violently. Decrease or increase the rpm a notch, the vibration will disappear. For some boats, this natural frequency will be far below or far above the normal rpm range of their motor. I wouldn't worry about it except to avoid running the motor at this rpm.
Get it fixed now
If the motor mounts haven't been changed in the last five years or so, do it now. I recently went through the fun of having to replace my transmission and numerous other parts on my 1983 H30 because the motor mounts were shot. They allowed the motor to vibrate excessively which caused the rear seal of the transmission to go out. It made a strange knocking sound before it went out. We happened to be out aways (5+miles) from shore and ended up limping home, but when I got there, I was there for the rest of the season. $3000 later, all is well. The mounts for the 2GM are about $120-130 each. replace all four and have the engine aligned. check the dripseal/dripless seal and stern tube when you are in there. Also make sure the cutlass bearing is good and the rear seal on the transmission. When they had mine apart, I had them replace everything but the prop and the prop shaft. This summer will be much better for sailing, knowing that the drivetrain is in like new condition. Hope this helps.
If the motor mounts haven't been changed in the last five years or so, do it now. I recently went through the fun of having to replace my transmission and numerous other parts on my 1983 H30 because the motor mounts were shot. They allowed the motor to vibrate excessively which caused the rear seal of the transmission to go out. It made a strange knocking sound before it went out. We happened to be out aways (5+miles) from shore and ended up limping home, but when I got there, I was there for the rest of the season. $3000 later, all is well. The mounts for the 2GM are about $120-130 each. replace all four and have the engine aligned. check the dripseal/dripless seal and stern tube when you are in there. Also make sure the cutlass bearing is good and the rear seal on the transmission. When they had mine apart, I had them replace everything but the prop and the prop shaft. This summer will be much better for sailing, knowing that the drivetrain is in like new condition. Hope this helps.
Check your Prop
Afouled prop will cause the same affects. My will thump when RPMs get up to about 1200
Afouled prop will cause the same affects. My will thump when RPMs get up to about 1200
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