1971 Grand Banks 42 Shaft Replacements or Repair

[DaveMedd]

My yard, which I will say is trustworthy, has reported that my port shaft is .020 out (20 thousandths) at the coupling end and starboard is .008 (8 thousandths) at the taper. There is also pitting on both.

They said about 2x to replace with Grade 19 shafts over repair. And they don’t think they could repair the 20 thousandths.

My sense is to replace. But am I being too perfectionist?

 

[Comodave]

Welcome aboard. Sorry I am not sure so I won’t give an opinion.

 

[SteveK]

I don't doubt the costs quoted to you. I would like to know that your shafts are aligned. Can you turn over by hand using the prop?
Did the shafts wear and that is why replacement is on the table?
Take a read on the following links.

Part I
https://stevedmarineconsulting.com/the-ins-and-outs-of-engine-and-shaft-alignment/
Part II
https://stevedmarineconsulting.com/the-ins-and-outs-of-shaft-alignment-part-ii/

 

[DaveMedd]

Steve

I’ve read many of your articles previously - thanks for posting those - always amazing help.

The shafts turned but not freely. I’ve replaced all six cutless and have replaced the couplings with split type. On port shaft, Prior owner had used masking tape to increase shaft diameter at the coupling. My guess is the bow in the shaft probably wore the down the circumference of the shaft at the coupling. And he was just trying to get it to work. She’s a woody boat so the vibrations weren’t actually that bad.

The cutless in the logs were trashed. The two in the struts were ok but replaced them anyways.

I’m thinking that with the pitting at the taper, some wear at the shaft log cutless, the .020 and .008 out on the shafts “true” that these probably need to be replaced. Else I’ll risk never really getting them aligned to a <.004 tolerance.

What do you think?

 

[jgwinks]

You are probably right about the misalignment wearing out the coupling-shaft interface. Mine did that too but it was pretty far out. The pitting is a concern too, it's crevice corrosion starting to occur. Yes, I'd go ahead and replace them both. Aquamet 22 is better than A19, especially for salt water. If the old ones are A19, it's probably why they're pitted. And engine alignment is just as critical as the shafts being straight, so make sure that's done correctly as well. With a woody it needs to be at least checked about a week after relaunch, the hull may take a slightly different shape while on the blocks then slowly revert to original in the water. It's enough to change the alignment. Happens with glass too, it's just worse with wood.

 

[SteveK]

SteveK here, the articles are SteveD

Going to ask again if the alignment is true, the shaft is not bent.
Is the boat out of water, the shaft disconnected from the tranny and still stiff to turn by hand. with things dry I would expect some stiffness. No surprise there is shaft wear on a 51 year old. Mine is also 51 yr old and I can freely turn when wet, a bit stiff when dry on hard.
Masking tape used as a shim, I don't think so, that is a new one.

The cutless in the logs were trashed. The two in the struts were ok but replaced them anyways.

That is what is suggesting out of alignment to me.

 

[Lepke]

How long will you keep the boat? Forever, get new shafts. A couple years, change the bearings, align best you can and enjoy your boat. Shafts with a less than perfect alignment can go years without much change. Deal with it when you sell or scrap.
Wood boats out of the water and improperly blocked can go out of align and you always recheck in the water.
Shaft repairs are best done by a shop that specialized in shaft repair. The average boat yard probably can't do as good of job. If you're at a yard that mostly does commercial boats or large yachts, you have a better chance.
Worn shafts are repaired by welding and then turning or hard chroming the wear back to spec. Shafts that already have crevice corrosion are probably not worth the cost of repair.
If you decide on new shafts and a proper job, better verify the 3 bearings on each shaft are still in align. I have an 83' wood boat with 3 bearings per shaft and 3 section shafts. If one bearing is slightly out of align, it's impossible to get a good alignment, and it causes wear. Bearing after shaft seal should have a water supply.