I have a vibration that seeming comes from the prop shaft at over 1200-1500 RPM. Also, I have noticed that when I am motoring against the current, it is worse than when motoring with it. Has anyone else had this problem? I realize the boat is 17 years old and is likely to suffer from some fatigue, but I had a new prop shaft put in and the vibration continues. Strangely, it is not consistent. I motored all the way from Oriental, NC to Wilmington, NC (about 100 miles) with very little vibration, however some days it was very noticeable. Any help would be appreciated. Thanks.
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Engine Caused?
If the vibration is so intermittent and variable then I'd suspect something connected with the engine. Air in the fuel line will cause a roughness in the engine which can cause vibration. The next time you're out runing along at cruise try cracking the nuts on the injectors (just slightly) for a second or two. If there is any air in the line it will bleed out and the engine will immediately run smoother. Conversely, if there isn't any air in the line then there'd be no change in roughness. Air in the line can come from a myriad of sources.
If the vibration is so intermittent and variable then I'd suspect something connected with the engine. Air in the fuel line will cause a roughness in the engine which can cause vibration. The next time you're out runing along at cruise try cracking the nuts on the injectors (just slightly) for a second or two. If there is any air in the line it will bleed out and the engine will immediately run smoother. Conversely, if there isn't any air in the line then there'd be no change in roughness. Air in the line can come from a myriad of sources.
vibe could be caused by....
A worn cutlass bearing. Or it could be caused by poor alignment of the prop shaft. And check to see of the strut that houses the cutlass bearing has not worked itself loose due to vibration. The nuts/bolts for the strut are located in the small floor storage bin behind the aft berth engine access. Lastly is could be that your prop is out of balance. On the prop/engine alignment....the single most common mistake that is made when replacing or just aligning the prop shaft is to do the alignment while the boat is out of the water. All fiberglass boats change shape when they are out of the water supported by stands or cradles. The shaft alignment should be 'roughed in' while on land, and then fine tuned in the water. Your shaft is aligned when (with flange bolts only snugged)there is no more than a .003" difference in the gap between the flange of the shaft and the flange of the xmission. Aligning the prop shaft to the motor is not hard, just takes time and patience. The motor mount is designed so that you can move the motor up/down or side-to-side as needed to get the motor angle just right for the prop shaft. The only way to check the alignment is to unbolt the flanges and move the shaft back and see if the separation of the flanges allows the motor to shift position. If the motor moves even slightly when the flanges are separated then the shaft is misaligned. If you do separate the flanges for this test, mark both flanges so you can rebolt them in the same position as before. Based on your comments about how the vibe is worse when against the current, my guess is that the cutlass bearing is the prime suspect. Also if the cutlass bearing is the culprit, you will have to remove the prop to get at it. At that time have the prop re-balanced (can't hurt). Also it's worth noting that a worn bearing can ruin your new prop shaft, so don't let it go. Checking the bearing while in the water would be very difficult. The check is to tug on the shaft and see if there is any play - meaning can the shaft move side-to-side in the bearing. It should move only very slightly (I would say no more than 1/64th of an inch) in a good bearing and will move noticably, perhaps as much as 1/16th, in a worn bearing. These are my subjective guesses and I don't claim to be an expert. The above is based on my own experiences replacing the prop shaft, the prop flange, and the cutlass bearing on my own 28. Happy hunting..... Mike
A worn cutlass bearing. Or it could be caused by poor alignment of the prop shaft. And check to see of the strut that houses the cutlass bearing has not worked itself loose due to vibration. The nuts/bolts for the strut are located in the small floor storage bin behind the aft berth engine access. Lastly is could be that your prop is out of balance. On the prop/engine alignment....the single most common mistake that is made when replacing or just aligning the prop shaft is to do the alignment while the boat is out of the water. All fiberglass boats change shape when they are out of the water supported by stands or cradles. The shaft alignment should be 'roughed in' while on land, and then fine tuned in the water. Your shaft is aligned when (with flange bolts only snugged)there is no more than a .003" difference in the gap between the flange of the shaft and the flange of the xmission. Aligning the prop shaft to the motor is not hard, just takes time and patience. The motor mount is designed so that you can move the motor up/down or side-to-side as needed to get the motor angle just right for the prop shaft. The only way to check the alignment is to unbolt the flanges and move the shaft back and see if the separation of the flanges allows the motor to shift position. If the motor moves even slightly when the flanges are separated then the shaft is misaligned. If you do separate the flanges for this test, mark both flanges so you can rebolt them in the same position as before. Based on your comments about how the vibe is worse when against the current, my guess is that the cutlass bearing is the prime suspect. Also if the cutlass bearing is the culprit, you will have to remove the prop to get at it. At that time have the prop re-balanced (can't hurt). Also it's worth noting that a worn bearing can ruin your new prop shaft, so don't let it go. Checking the bearing while in the water would be very difficult. The check is to tug on the shaft and see if there is any play - meaning can the shaft move side-to-side in the bearing. It should move only very slightly (I would say no more than 1/64th of an inch) in a good bearing and will move noticably, perhaps as much as 1/16th, in a worn bearing. These are my subjective guesses and I don't claim to be an expert. The above is based on my own experiences replacing the prop shaft, the prop flange, and the cutlass bearing on my own 28. Happy hunting..... Mike
Been down lately??
Have you gone over the side witha mask and given it a look see or a feel? Could be some fouling on your propshaft, or a barnacle or two making for offbalnce in the prop. The cutlass bearing is another point. when did you last change it?? When mine corroded and the rubber slipped out of the housing, it was "clunking" as it knocked around in the housing. Jim McCue
Have you gone over the side witha mask and given it a look see or a feel? Could be some fouling on your propshaft, or a barnacle or two making for offbalnce in the prop. The cutlass bearing is another point. when did you last change it?? When mine corroded and the rubber slipped out of the housing, it was "clunking" as it knocked around in the housing. Jim McCue
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