Prop shaft slipping axially in coupler?

[korey]

Here's a new one to me... Last night I decided to dig into investigating a weird vibration that has been getting worse over the last few weekends. As with most stories that start with that phrase, I opened can of worms...



I had hastily installed my good prop a few weeks ago after a repair and didn't lap it to the shaft. At that time I also noticed some wear in the key, but didnt have a replacment. So i went to pull it off last night and check itout, properly lap the prop to shaft, and replace the key, nut and pin with new parts.

Except the prop's hub was closer to the strut than it ever was before, and I couldn't get the fingers of my puller in between the two... I've measured for replacement prop shafts before and the advice that I was given was that there should be about 1/2 to 1 times the diameter of the shaft between the prop hub and the strut - so on these 1" shaft boats, 1/2 to 1". I always thought it suspect that this saltare never had more than 1/8", and then when I checked it out this week, and pretty much ZERO. Once I did get it apart, it showed signs of having rubbed:


Anyone have any input on how much gap is between your prop hub and strut on a saltare? Ever had your coupler removed from the trans and have any input on the amount that the shaft goes into the coupler?


So, as usual, I dug deeper. I found that the entire shaft had pushed further into the boat, and slipped in the coupler at the end of the transmission. Angularly it's fine - the keyway in the coupler is perfect - but it slipped axially, deeper into the coupler. This affects drive geometry, clearance with both the hull and between the prop hub and strut, and my PSS shaft seal - that explains the water that's been showing up in my bilge. I have the slide hammer thingy (technical term) that attaches to the prop nut threads used for separating these assemblies, so I pulled on it and it moved rather easily. I mean, it took a pretty good blow from the slide hammer, but not like I'd expect. There is no slop in the coupler or anything. My other boats have either been shrink fit steel to steel, or taper fit steel to aluminum - this supra is a press fit (I guess) steel to brass with a key. It also has set screws, so I made an adjustment to make the end of the prop shaft even with the flange end of the coupler and cranked down the set screws.

Has anyone else run into this? Obviously the axial thrust from the shaft needs to be transmitted to the transmission and the hull of the boat to move, but I'm thinking that the end of the shaft should stay flush with the inside surface of the coupler, and not extending to touch the input shaft of the transmission like I found it. My set screws were loose (and one missing). I guess that could be the culprit, or is my assembly just too worn?

What it really needs is a new shaft/coupler assembly, and a full alignment - strut included. I've done it before, and I'm not afraid to do it again, but there isn't the time for that before a houseboat trip starting tomorrow... I just hope I can get through this weekend. These $500 here and there problems would make a really nice payment on something that didn't have these problems... The worst part is that the boat performed very well this past weekend. We put about 6 hours on it, mostly heavily weighted for surfing, and aside from the vibration under heavy load that I was looking to investigate, she did spectacularly!

[wotan2525]

I never had that problem but it sounds like your set screws are the issue. I believe on the coupler that there should be two set screws in the same bore. The top one locks in the bottom one. At least this was my setup from the factory.

The "new style" couplers prevent any slippage by adding a nylock nut to the end. It does require upgrading your shaft at the same time. Probably not worth it unless you need to replace the prop shaft.

[chris young]

Sounds to me that the coupler was removed once before and re installed. This is supposedly a no no with these types of couplers. Once removed they should be discarded. I replaced mine when I pulled the shaft with the buck algonquin split type which tightens by squeezing the shaft.

[korey]

mmmhhhhhmm... The boat does have an aftermarket dripless shaft seal. i bet the shaft was pulled to install that.

[Salty87]

Anyone have any input on how much gap is between your prop hub and strut on a saltare? Ever had your coupler removed from the trans and have any input on the amount that the shaft goes into the coupler?

Shaft has been replaced a time or 2 and this is what it currently looks like. Coupler was replaced each time as well. Been a while since I messed with it but from what I recall there isn't any room for the shaft to seat further into the coupler. Could be possible someone installed a shaft on yours that was on the short side.

[michael hunter]

Contact TitanTN Rob had his shaft pull out of his Saltre a few years back . I don't know how he fixed it.

[TitanTn]

Contact TitanTN Rob had his shaft pull out of his Saltre a few years back . I don't know how he fixed it.

Yep. I had it pull out several times. The original coupler is a pressed fit and is possible to use many times as long as the tolerances remain for the press fit. There isn't a nut on the inside of the coupler on these older, press fit types, but I had my shaft tapped and the coupler had a recess cut into it to accommodate a washer and an Allen bolt to secure the coupler to the shaft. It's very tight now and works great. Without the press fit, the set screws are not enough to hold the shaft.

I agree with Salty, I wonder if your shaft might be shorter than stock. My Saltare looks like his picture too and the shaft could only possibly slide 3/4 inch towards the engine before my modification.