Is New Shaft Needed?

[Frank Vernet]

As many of you know, I am doing a lot of needed engine work this winter.

I recently posted a series of pictures on the shaft log seal and this post is related. It is a close-up of the section of the shaft that goes through the cutlass bearing.

As you can see, the shaft is scored and it was suggested that I replace it. I initially thought "why not just smooth it a bit much like is done for brake rotors" but then realized that it would be loose in the cutlass bearing. I then thought "Just run the other (i.e., smooth) end through the bearing!", but as I was gently reminded "One end of the shaft is tapered for the prop, The other end is cut and keyed for the coupling. The shaft cannot be end-for-ended."

So my question is - as this is not a safety issue would you replace the shaft? The grooves may cause the cutlass bearing to wear faster/unevenly but how big a problem is this realistically?

Thanks as always.

[JWSutcliffe]

A replacement shaft is relatively low cost. If you have the old one out already, I would replace it. I replaced mine last season and installed a dripless seal, which completey eliminated any leakage. It was worth every penny.

[Maine_Buzzard]

$350 - 400 for a new shaft, it will be ready in three weeks. (Just got mine from Hamilton). You have some crevice corrosion going on too, so that's not going to help.

I killed a cutless in 50 hours with an old bronze shaft much worse than that. Replacing it is cheap insurance.

[Klem]

Chances are that you need a new shaft but there are a few simple checks that you can make if you really want to save it.

The shaft must be the correct diameter to maintain the appropriate clearance with the cutlass bearing. You can check the diameter at several different points along the shaft and at different clocking and if they all check out okay, then you this aspect is okay.

The other issue is the scoring on the shaft. The shaft needs to be smooth to get proper water film so you would need to turn off a tiny bit of material to take these out. You can measure the depth of the deepest scoring and if taking off that much would still leave you within the original diameter spec, you could do that. The fact that you can see this in the pictures suggests that they are significantly too deep to do this but the only way to tell is to measure it.

Also, as suggested, you have some pitting so you might consider replacing it for that reason.

[Frank Vernet]

Thanks you gents. As always the CD community offers sounds advice.

For the reasons stated above, I will replace the shaft.

[Tom Keevil]

I agree, that were I in your position, I would get a new shaft. Nevertheless, I wonder how large a risk would it be to use a scored and pitted shaft. What is the failure mode for this? Has anyone ever heard of a shaft failing, and if so, what were the circumstances? Are you taking a real risk if you don't replace it, or are these just points for John Vigor's black box?

[JWSutcliffe]

Try

http://www.deepblueyachtsupply.com/shaftguide.aspx

My replacement was under $200., the service was fast, and the shaft quality was excellent.

[Ron M.]

I can second Skip's recommendation for supplier.........DBYS was fast and reasonable.
While I'd prefer to do business locally a 40% savings was significant.

[Oswego John]

I totally agree with what Skip and others said. Taking all things into consideration, availability, cost, service, and time, I think that going new is the way I would also go.

Now, having said that, let me mention another way to handle the shaft problem. Maybe this other method will probably sound rather unorthodox to most, but for those able to, and have access to tools and equipment necessary, it is most doable.

My late brother and pal had a twin screw workboat. One of the prop shafts got gnarled up so he put the boat on cribbing and proceded to pull the bad shaft.

My brother wasn't just a tacker or a weldor. He was a professional weldor with certification in many disciplines. In the metal trade there is a term that may make some people cringe a bit. Mostly, we worked as a two man team. One is the weldor, the second person is the weldor's pimp. Hey, I'm sorry but that's the way it is. My brother was our weldor. I was the engineer in charge of preparation prior to his doing his thing.

I digress. Getting back to the shaft, after the shaft having been cleaned up, my brother went back and forth, weaving, beading and filling the valleys with wire rod that supposedly had a tensile strength harder than the shaft being worked on.

After filling the voids, the shaft was miked and placed in an engine lathe. All of the high spots were turned down to within .001" or .002" of the shaft's diameter. Then the shaft was polished first with emery cloth and finally with crocus cloth. That reworked shaft was smoother than a baby's six. It was impossible to see where any damage was beforehand

Now, to reiterate my earlier statement, go buy a new shaft.

O J