Shaft coupling set screws - Shape/wear

[sveinung]

My prop shaft came out on me yesterday after a test run in reverse on a mooring, a mild heart attack after seeing all the water come in I'm out there to put it back together.
Set screws came out fine with some WD40 and convincing and axel is back in. Screw holes align with the dimples on the axel, but before putting it back together i took a closer look at the set screws.
I expected some sort of convex tip, to be the male part into the dimple, but mine is rather the opposite.

Should the screew look like this? Is there a ball bearing ball or something that should be between screen and dimple to fill it?

It's a Yanmar 2GM20F in a Pearson 303 '87, 1" shaft.

[sesmith]

If the prop shaft came out of the coupling, you have a problem. It should be a very tight slip fit (tap fit...shouldn't go together by hand). There's likely too much clearance and you will need to have a new coupling fitted to the prop shaft. You may need a new shaft, as well, if it's been loose for a while. Get someone to check it out for you.

[BillKny]

That is not a proper set screw. That is a sawn off piece of threaded rod.

You are quite correct to be dubious about its ability to engage properly with a shaft "dimple."

[phorvati]

I had some issues with that, but on a bigger boat, its a bigger ordeal. That screw is not a set screw. You should get a real set screw, but its too late. You most likely need new coupling. After mine came out, my PSS shaftseal collar saved it from total disaster. I needed a seatow, haulout, new shaft, new coupling and new PSS and I ended up getting new transmission coupling with seals as well to make sure mating surface is fresh.

I think since it came out, your shaft is probably worn beyond service and so is your coupling and keyway. My keyway was disintegrated. I ended up getting a "split coupling" so that I can tighten and "grip" the shaft really good before adding set screw. There is a rule of length of coupling as to how it pertains to shaft diameter. I think it 4-5 times to 1. I had a 3.5" shaft coupling length on a 1.5" shaft. Not a good ratio. And it wobbled off, meaning progressive worsening of engine alignment made set screw break and in reverse shaft pulled out grinding the key way, and ruining the coupling and shaft in the process. Sure telltale was me braking set screws and having to drill them out twice in span of 4-5 years. As another person said, its an interference fit. It needs to be tapped pretty good to get on the shaft. And it needs to be "square" to the shaft. Its something a machine shop does.

[sveinung]

Very ominous responses, but no worries, the shaft is looking nice and smooth (besides the dimples), and it was a very snug fit taking quite some convincing to put back together.
So i guess there's one answer to "do i need new set screws", and it was yes. I'll order some new ones.

[Gaia]

Another educational thread! Is there room to put in two set screws? One on top of the other to lock the first one in place? I have been doing that on our autoprop but do not know if it is recommended procedure. Just makes sense to me but I stand ready to be corrected.

Jim sv Gaia

[RSB333]

When I had some transmission issues, I took the opportunity to have the shaft and coupling trued at a shop that services commercial fishing boats. They first evaluated to see if mine was beyond repair, then polished and trued the shaft and coupling and re-balanced the prop as well for around $200.
RSB333

[sveinung]

Pretty sure it's the original set screws phorvati & BillKny, sure looks like set screws, got square heads and holes in them for the seize wire.

The question was what the tip was supposed to look like, seems like it's either cup or point tip for the shaft dimples. Was hoping someone knew what was used on the Pearson shafts, but i can reach out to a marine diesel store.

From what I can tell it's a 7/16-14 x 7/8 length.

[Newf1]

When you say,"dimple", are there actual dimples drilled in the shaft for the set screws or are there just marks on the shaft from the set screw pushing on it? If there are drilled dimples, are they smaller in diameter than the diameter of your set screw? If they are, you could just grind a slight taper on the end of the set screw to set down into the dimple. (any photo of end of shaft showing the dimple?)

[Newf1]

Another question. Was that nut a part of the original set screw installation? I have never seen that before, especially with set screws that have holes so you can wire them together.

[sailorboy1]

I don't think that set screw is correct. It should have a pointed tip for the shaft dimple and have a hole in the head so you can lockwire it so it can not turn.

IMO of course

[pcmm]

Originally Posted by sveinung

Pretty sure it's the original set screws phorvati & BillKny, sure looks like set screws, got square heads and holes in them for the seize wire.

The question was what the tip was supposed to look like, seems like it's either cup or point tip for the shaft dimples. Was hoping someone knew what was used on the Pearson shafts, but i can reach out to a marine diesel store.

From what I can tell it's a 7/16-14 x 7/8 length.

That looks like it started out life as a set screw ( the head is correct) but there shouldn't be a nut there and the tip should end in a cupped point. The square head should also have a hole drilled through it for mousing wire.

[sveinung]

Originally Posted by pcmm

That looks like it started out life as a set screw ( the head is correct) but there shouldn't be a nut there and the tip should end in a cupped point. The square head should also have a hole drilled through it for mousing wire.

Yes, it's definitely the set screw, but the point is completely worn down as it worked its way out. That way my initial question basically, "shouldn't these have a protrusion to go into the dimple".

I've seen other forums and articles mention using a nut for seizing the screw in place so i don't think it's that uncommon, there is a hole in the head for mousing wire that was working, the bolt didn't rotate much until i removed the wire and used a generous amount of force and penetrating oil.

The cone point looks the most like the dimple, but you mention cupped pcmm, what's the difference in their application?

This is the only picture I have of the dimples on the shaft, pretty small here.

[steamgoat]

Once you have it back together,put a shaft anode on behind it,it may save the shaft from escaping in future. + it’s a good place to keep a spare.

[Newf1]

Set screws come with all sort of tip shapes,,,,,,cone shape, oval, convex etc etc. It may not have been the correct type installed. The end of your bolt does not appear to be damaged or at least from what I can tell in the photo. If a correct screw was originally installed in the dimple I would think that you would of had to have a whole lot of vibration to wear the tip off and allow the shaft to slide out.