Initial 50 hour shaft alignment “adjustment” Yanmar 45

[hvac&r tech]

Getting near 50 hours on my new Yanmar 45 and I see the Yanmar book recommends not just to “check” prop shaft alignment, it says flat out to do an “adjustment” after initial 50 hours.

I hear a bit of high pitched whine between about 1100 and 1600 revs , anyone have a take on what the whine may be? Some people I’ve asked have said it’s almost certainly prop generated harmonic vibration. They have me convinced. Now my new professional mechanic tells me about the multi item 50 hour service that’s coming up and I just out of curiosity look up what’s involved to know what to expect

. Noticed the shaft alignment adjustment recommendation. Now I’m glad I looked at the maint schedule, one possible easy way to see if the high pitch sound I hear is from a prop imbalance/ harmonic vibration like I thought, or the shaft needing adjustment- is to get the service including the adjustment and see if it quits I suppose.

anyone get a professional to do a Yanmar “initial 50” hour maintenance like the manualrecommends? Did the yard you used give you any details about the “propeller shaft adjustment”?

 

[Davidasailor26]

We had the 50 hour service done by a tech. I don’t remember whether any adjustment to the alignment was actually needed in our case, but it makes sense to at least check at that point, once the hull has settled in the water and gone through any shape changes from that. I wouldn’t read too much into the difference between “check” and “adjust”. The first step of adjusting to to check the alignment, then to trim the mounts as needed. So if the initial check showed everything still aligned the job would be done.

Since the noise seems to be happening at specific RPM ranges, and not just building with increased RPMs, the harmonic theory makes sense to me. But a check definitely makes sense at this point anyway.

 

[RoyS]

Try turning the shaft by hand while listening and feeling for interference between the shaft and the stern tube. The shaft should rotate freely and quietly. You could dive in and check that the shaft is centered in the stern tube. If everything looks and feels OK then I would just check that all the motor mount and shaft coupling hardware is tight. Fasteners inadvertently left loose during assembly tend to back off from vibration after a few hours of operation. Look for those.

 

[Ralph Johnstone]

IMO all boats need to be checked and aligned (one satisfies the other) at least at 50 hrs. after they have settled in as per @Davidasailor26 . I did mine and the couplings were about 0.008" out when they should have been 0.004" max. for that size coupling. I can't see how a shaft can be aligned if the boat has never been in the water since coming off the production line when the new owner receives it.

I imagine that is why you see so many cutlass bearings being replaced. I have maintained a shaft alignment of 0.002" since six months after receiving the boat new in 1998 and now have about 2800 engine hours. The cutlass bearing has no radial movement.

 

[hvac&r tech]

IMO all boats need to be checked and aligned (one satisfies the other) at least at 50 hrs. after they have settled in as per @Davidasailor26 . I did mine and the couplings were about 0.008" out when they should have been 0.004" max. for that size”

Is it pretty easy to get down to and acess where you measured the engine output shaft to propeller shaft misalignment on your boat? What method and tools do you use to check alignment? Straight edge tight to the coupling hubs and feeler gages to measure the gaps or something else? Did you use an alignment check method that left the coupling bolted together during your check or did you disconnect the prop shaft from the motor and spin the prop shaft independently while doing the alignment check? Do you use rule of thumb tolerances derived from diameter of shaft and rpm or are they printed in Yanmar / Beneteau manual? When you’ve found misalignment, was it easy to determine what needed to be loosened and subsequently retightened to adjust the propeller shafts center of rotation and did you use any pictorial or video reference the first time?

Wasnt thinking I was going to learn this all the way and maybe do this myself, but since I’m not hearing anyone saying they had this or that easy to understand explanations from a 50 hour service provider whether adjustments are almost always necessary, or that the kind of hum I describe others may have also noticed and was or wasn’t resolved with a 50 hour alignment adjustment- maybe I dig in myself. Thanks!

 

[Ralph Johnstone]

Your reply came printed in an unusual format so my answers are in red.

Is it pretty easy to get down to and acess where you measured the engine output shaft to propeller shaft misalignment on your boat? It's never easy .

Do you use rule of thumb tolerances derived from diameter of shaft and rpm or are they printed in Yanmar / Beneteau manual? Ball park is 0.001 per inch of flange diameter. I shoot for 1/2 of that which is not difficult if you are careful.

Did you use an alignment check method that left the coupling bolted together during your check or did you disconnect the prop shaft from the motor and spin the prop shaft independently while doing the alignment check? Alignment can only be done if the flanges are apart.

Check out this alignment attachment which I picked up years ago.