I have a vibration (knock) after 1200 RPM, can run at 5.5 knots on calm water, no tide current and no wind, but can not rev the engine above 1200 RPM without getting a "knock". I have a Catalina 30, with a atomic 4 engine...and am wondering if it is NOT a bent shaft, then it has to be engine aligment? Is there a method to aliging the engine with the shaft?
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check shaft bearing first
The knocking may be the result of a worn drive shaft bearing - they seem to last only a few years,depending on usage. If that is the problem, you should fix that before re-aligning the drive shaft. The re-alignment procedure is explained in the Universal engine manual. Don't know how easy it is - haven't done it myself before, but this Saturday I have a mechanic coming to my boat do do just that (he told me it takes about an hour)! I suppose it will not be much different with an Atomic engine, although some details may differ.
The knocking may be the result of a worn drive shaft bearing - they seem to last only a few years,depending on usage. If that is the problem, you should fix that before re-aligning the drive shaft. The re-alignment procedure is explained in the Universal engine manual. Don't know how easy it is - haven't done it myself before, but this Saturday I have a mechanic coming to my boat do do just that (he told me it takes about an hour)! I suppose it will not be much different with an Atomic engine, although some details may differ.
Could be loose zinc
The knocking might also be caused by a loose zinc - depending upon whether yours in installed on the end of the prop/shaft, or on the shaft itself, a zinc that is worn can become loose on the shaft and might cause the knocking noise. Good Luck! Tim Brogan April IV C350 #68 Seattle
The knocking might also be caused by a loose zinc - depending upon whether yours in installed on the end of the prop/shaft, or on the shaft itself, a zinc that is worn can become loose on the shaft and might cause the knocking noise. Good Luck! Tim Brogan April IV C350 #68 Seattle
Thanks for the replies...keep more coming.
The Zinc is new and fastened well, as for the bearing..."cutlass"... new too. Not sure if it might be a bent shaft caused by the haul-out or when putting her back into the water??? When I bought the boat it had the "knock". I'll be checking for a bent shaft this winter when I have her hauled, but have the feeling it is engine aligement... thanks for the responses and info on where it describes the process of aliging. After you have your work done, let me know some of the technique that was used, especially if it is not in the manual. Thanks Denny
The Zinc is new and fastened well, as for the bearing..."cutlass"... new too. Not sure if it might be a bent shaft caused by the haul-out or when putting her back into the water??? When I bought the boat it had the "knock". I'll be checking for a bent shaft this winter when I have her hauled, but have the feeling it is engine aligement... thanks for the responses and info on where it describes the process of aliging. After you have your work done, let me know some of the technique that was used, especially if it is not in the manual. Thanks Denny
alignment done
and it took about an hour, but the guy knew what he was doing and I was lending him a hand. It goes exactly as the manual says - I misled you BTW, the description is not in the engine manual but in the Cat30 owners manual. Has an exploded view of the shaft and coupling. I don't have a scan into .pdf facility, otherwise I could upload it. Someone else perhaps? The process involves detaching the coupling. You may wish to check the two bolts,which should be attached to each other by a wire. In my case they were dangerously loose! Then you loosen the engine-mounts (you will probably need to apply a liberal dose of WD40 first) and juggle the thing whilst occasioanlly rotating the shaft so as to achieve a 0.003" gap between the flanges. I am not sure if I would do it without competent help myself next time, but it certainly is not rocket science. The manual advises to check the alignment once a year. That is a simple process, just stick a feeler gauge between the flanges. It should certainly be done after replacing a cutlass bearing. The result of the exercise was a very noticeable reduction in vibrations, especially at higher revs.
and it took about an hour, but the guy knew what he was doing and I was lending him a hand. It goes exactly as the manual says - I misled you BTW, the description is not in the engine manual but in the Cat30 owners manual. Has an exploded view of the shaft and coupling. I don't have a scan into .pdf facility, otherwise I could upload it. Someone else perhaps? The process involves detaching the coupling. You may wish to check the two bolts,which should be attached to each other by a wire. In my case they were dangerously loose! Then you loosen the engine-mounts (you will probably need to apply a liberal dose of WD40 first) and juggle the thing whilst occasioanlly rotating the shaft so as to achieve a 0.003" gap between the flanges. I am not sure if I would do it without competent help myself next time, but it certainly is not rocket science. The manual advises to check the alignment once a year. That is a simple process, just stick a feeler gauge between the flanges. It should certainly be done after replacing a cutlass bearing. The result of the exercise was a very noticeable reduction in vibrations, especially at higher revs.
Not too tough to check the alignment,
there is a little fore & aft movement of the shaft when it is disconnected at the coupling. You move shaft aft till flanges of coupling are separated, then move shaft forward till flanges "kiss". In a perfect world they would mate perfectly, in our world they will touch at one edge and be separated at the other edge. Your goal is to see that this gap does not exceed .003, if it does you must re-align.
there is a little fore & aft movement of the shaft when it is disconnected at the coupling. You move shaft aft till flanges of coupling are separated, then move shaft forward till flanges "kiss". In a perfect world they would mate perfectly, in our world they will touch at one edge and be separated at the other edge. Your goal is to see that this gap does not exceed .003, if it does you must re-align.
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