Getting prop back on

I need some help getting my prop back on. This all seems silly, and unnecessarily tricky.

Long story. We have an 89 Sunsport and boat in a shallow river (4-8’). Granted, this isn’t the best idea, but it’s close to home, the water is flat, there is a marina with a slip on the water, and this means we can get in a couple sets on the way to work. There is a deeper river with a marina ~1 hour away, but that’s too far for the dawn-patrol run before work.

Anyway, as it won’t surprise you, after a couple years there we had a bit of vibration in the back end of the boat. We pulled it out of the water and took it to the shop last September. They said they wouldn’t have time to work on it for 3 weeks, which meant the end of the season. They told me the prop was “garbage.” It looked a little dinged up to me, but he assured me it was trash. So, I took the boat home, called Skidim, asked them to send me a new prop that would make me happy. They sent an OJ 4 blade 13 x 15.5. I put it on and boy did it go like stink. Smooth as silk. Beautiful hole shot and better top end. We happily skied well into November.

Over the winter I found a shop that welds and rebalances props. I pulled the new one off (yes, we dinged it up already) and got the old prop and new prop cleaned up. Thing is, when I went to pull the new prop, I found it was farther up the drive shaft than the old prop sat and that I had to unscrew the little cup from the prop puller to get the prop puller on. It popped off fine though.

I also stumbled across some comments about laping the drive shaft. This sounded like a good idea. I put the new prop on and drew a line on the drive shaft with a sharpy. It’s a bit higher up than the old prop (picture is with the old prop on and you can see a gap between the top of the old prop and the line). I’m not happy about how far up the new prop sits. When I spun it with the blue dye, it looked pretty good. Still, I’m not happy with how far up it sits and I wasn’t keen on laping it and possibly moving it farther up the shaft.

Also, over the winter I bought a new keyway, new nut, and new cotter pin, because that seemed all like a good idea. The new keyway sits nicely in the drive shaft slot. Thing is, the slot in the propeller is tappered on both ends. So if I start with the keyway in the drive shaft, I can’t get it to slip into the propeller. And if I start with it in the propeller, it won’t slip over the teeth on the drive shaft.

It turns out that the old keyway was in two pieces. When I put the new prop on last fall, I only used one of them because the other one was stuck in the old prop and I didn’t notice it. The old keyway doesn’t look like it was ever one piece that split. Just like two pieces. And I can’t get them to fit together back in the slot. They just seem too big. In the end, I can get the old propeller back on with one of the old keyways, but I can’t get the old prop on with the new keyway and I’m not happy with how far up the driveshaft the new prop sits with either set up.

So I put the old prop on with ½ the old keyway, a new nut, and new cotter pin. This doesn’t seem quite right. But it fits all snug.

Thoughts? I must be doing something daft.

What is it that bothers you about where the new prop sits? How close is it to the strut?

If you ran it last year and loved it, I would put it right back on and call it good. You may have to modify (grind) the new key to get things to fit just right. It doesn't need to be the full length of the slot in the shaft, or the full length of the prop. As you've probably read, it's really the lapping and the taper that holds things together. The key is more of a safety mechanism, it's not the primary thing that keeps the prop from spinning under load.

I guess you have it all back together now, but you need to know if the prop sits as far up with the key and without. This is very important, as you don't wan the key to be stopping the prop from seating on the taper. Any time you replace a prop you should use a new piece of key stock, and very carefully clean the keyway on the prop so that the key is free to slide in the keyway on the prop without being loose. The key should be snug on the shaft, ie it takes a light tap of a soft faced hammer to seat it in the shaft. As far as where the prop sits on the shaft, it's much more important to have it properly seated than it is as to where it is as long as there's space to the strut. I lapped mine a bit too much and it sits quite far up the shaft. As for putting the blue on the shaft and turning it, that's not how to check. you are supposed to have the inside of the prop clean, and blue the shaft and then slide the prop on with the key in place, then pull it and see how much blue has been transferred to the prop, or how much has been removed from the shaft.

I suspect the other prop was further down the shaft because it was riding on that double key thing you had in there, which is not good.

I would not worry about where the prop sits, so long as it still has thread to tighten it and it is clear of the strut. Lapping it correctly will have a negligible affect on how far up the shaft it sits, so be sure to lap it properly.

The key does not prevent the prop from spinning on the shaft. The taper fit does that. If the taper is not lapped for an even fit, then the key will only last a matter of minutes before it fails. Again, the key is NOT what holds the prop secure. The taper fit does that.

Just looking at the picture, I think your key is too long. You may have to cut it down to fit the deep groove in the drive shaft. Any length key in there at all will be just fine. The sole purpose of the key is to prevent the prop from spinning on the shaft during installation. with no key, you would attempt to tighten the nut and the shaft would spin inside the prop (remember you are holding the prop to prevent the shaft from spinning), so you would not be able to get the correct torque. Once the nut is torqued, the key serves absolutely no mechanical purpose.

So, don't over-think it. If the new prop runs the best and still has thread to tighten it...torque it down and go have fun!

Thanks all. My concern with the new prop is just that it is hard to get the prop puller on to get it off. That just makes me feel uncomfortable. When I took the old prop off last year, it was stuck tight. I'd hate to have that issue and try to take a tight prop off without the little cup keeping the prop puller on the drive shaft. Otherwise, it clears the strut.

Supra was not exactly precise on the placement of the engine motor mounts day-to-day. Your engine may have been originally mounted a little bit farther forward in the boat. Or possibly the shaft has been changed at some point in time. I presume you have had to modify the prop puller.