Propeller axle not centered

[Robert Nilsson]

Good Evening!I have a Hunter 34, built in 1983. I am very pleased with all aspects of the boat, but have a question in refrence to a minor tapping sound that occurs when running the engine at certain rpm:s. I have had this sound for years (since we bought the boat eleven years ago), learned to live with it, and also figured out where it comes from. It is moderately annoying when it occurs (typically at low rpms).What happens is: I figured out that the tapping sound comes from the stuffing box, and then the hull makes it echo loud enough to hear it. For the first years I thought it came from the Yanmar Diesel (in perfect care), but then I realized that the propeller shaft is not perfectly centered in the OUTSIDE opening of the stuffing box. Rather than being perfectly centered, it is about an 1/8" closer to port then starboard. At certain speeds the engine shakes sligtly (read lower rpm:s - after all, it is a diesel...), and thus the propeller axle taps against the bronze fitting. Have tried to move the engine slightly to starboard, which worked great - the sound disappeared - but the alignment was of course thrown off, so not a good idea. My shaft/engine is well aligned (no vibrations), and I check the alignment every spring three weeks after launch.Next idea (from a knowledgeable fellow boater that works with engines, etc.): With a file, or emery cloth, slightly grind on either the shaft or the bronze fitting, to allow an extra 1/16" (which would take care of the problem). Now, this would work, although here comes my question: Will this affect anything in a negative aspect? Is the bronze fitting (the stuffing box) made in SOLID bronze or is it hollow? Will filing an 1/16" at the very aft portion of the stuffing box (outside the boat) on the port side of the "hole" cause a leak? I can only assume that sometime in the boat's life prior to that we bought her a lift sling was put so that it may have bent the strut (the shaft is perfectly straight) slightly. I do not want to monky with the strut or anything else that is not necessary: things work well, and I just would like to get rid of the tapping sound. Would appreciate your thoughts...Thank you!Robert

 

[Roger Mummah]

Don't Run at that RPM

Hi Robert. Endless Summer is a 1983 h31 and her wonderful 2GMF bangs and jiggles at certain RPMs. Our solution is to NOT run at those RPMs. We too have done our best to keep the diesel in aligment, but like Capt Ron says "..All Diesels Do That..!" I looked into fixing it and even sent and received emails to/from the well known Nigel Calder about it. If you can't live with not using that RMP you can install a "flexible shaft coupler". That should do the trick, but the good ones are a thousand bucks (I think). I think Vetus makes them. There is also a SLIGHTLY flexible coupling called a "shaft saver" that might help. It is designed to provide a "break-away" coupling that SHOULD break before your shaft, propeller or iron/steel coupling break. It mounts between the two sides of your shaft coupling. I have heard that they can in some cases provide enough shock absorbing action to reduce "shaft knock". Like I said, we just don't run at noisey RPMs. Good luck. Roger and Susie Mummah s/v Endless Summer

 

[Don Alexander]

Correcting the Knock

We had a similar problem after doing some work on the engine mountings and fitting the of a PSS stern gland. Do you also have a PSS because it does not centre the shaft in the same way as a conventional stuffing box so the shaft can come into contace with the metalwork.I seriously recommend you do not grind the shaft as there is insufficient material to overcome this problem and the shaft would be ruined.Either way it is best to tackle this with the boat out of the water. Remove the flex rubber hose at the hull log tube end and look at the centring of the shaft in the log tube. Yours will be well out of alignment. Slacken the 6 bolts on the coupling flange to the gearbox and adjust the engine up or down and side to side to correct the centring. At this stage it need not be perfect.Now disconnect the coupling flanges and re-align the engine flange with feeler gauges as per the book, whilst keeping an eye on the shaft centring. It should be possible to achieve both together.Whilst doing this you may wish to fit one of the donut type of slightly flexible plastic vibration absorbers between the flanges as they are quite inexpensive. Make sure you fit the earthing strap as well to protect the prop.Regards,

 

[Peter Roach]

Mine taps also

Mine taps also. If it is coming from the shaft hitting the bronze fitting what is the problem with leaving it alone - unless it is really bothering you. I can now tell everyone "that is the way a Hunter 34 sounds"

 

[Kevin l. Woody]

I would not grind

Hello Robert,I’m often one that does not like to use force or grinders for fitting. I’m not very comfortable with the removal of material to either component. My guess is that in some degree the current “tapping” is limiting the engine movement. My fear would be that once we remove the 1/16th of an inch material, does that now allow the motor/shaft to move another 1/16th of an inch causing yet another impact? My second thought would be to make very sure that it is a metal to metal impact and not metal to fiberglass impact. If the vessel were ever presented to an environment that would cause us to use the running gear long term at the problem range of Rpm’s, could it actually cause a premature failure to the tube, stuffing box housing or shaft? Have you ever considered using a different type of sealing device? Some are made in such away which allows for additional clearance between the shaft and the bronze stuffing housing. Again though, if the current stuffing box is providing support in any axial rotation I would be careful that if it was removed,could the impact or motor/shaft movement increase creating more of a problem. Sorry to say, I would adjust my engine and strut back to its proper position. Hope this helps. Sincerely, Kevin L. Woody