What do I torque my prop nut to?

[chris young]

docdrs, you may be right, I may be crazy, but Keith Fenner, (the guy in the video) suggested it and he certainly seems very knowledgeable and practical. Since I lost my last one, I just didn't want it to happen again. I'm not the type that keeps changing props, so, until I hit something or break a shaft (which I die penatrant checked before I put it back in the boat) I won't be pulling the prop.

[SquamInboards]

Lapping is less about keeping it on and more about getting a perfect fit for smooth operation at speed and less stress on the keyway. As far as keeping it on, what docdrs said: nylock + cotter pin. Or a castle nut with a cotter pin right through it (same idea).

[chris young]

I lost my prop because it wasn't properly fitted, and I didn't notice the cotter pin was missing. So when I shelled out for a new 541, I wanted to keep it, and that's how I learned about lap fitting. I also took the opportunity to pull the shaft and die check it, so I was able to do the lap fitting with a rig to spin the shaft with a drill. I started doing it by hand, but it was taking forever, so I rigged something up so I could put the prop on the floor and spin it with a drill. It worked so well I actually went too far, but no harm done. If I was going to do it on the boat, I'd either rig something up to spin the shaft or the prop.

There are a couple of really good reasons to properly fit a prop, not loosing it is one, but the other one that is more important, is that your prop should not rely on the key to drive the prop. If the prop is just a little loose, it'll bang on the key, and this can lead to the shaft breaking. Apparently most shaft breakage occurs at the keyway for this reason. What many people don't know (I didn't) is that it's the fit that drives the prop, not the key. The key is there for safety in case the prop gets loose.
I don't want to spread any paranoia but that's also why it's generally recommended to replace the shaft coupler with a new one any time you remove it from the shaft. Cheap insurance against failure at that end as well.


It may be overkill to do the heating thing, but I'd rather be swearing and banging and heating when I finally need to get the prop off, then swearing and sweating and paddling to get my boat back to the dock with my prized 541 on the bottom of the lake. My boat stays in all season, and my dock is my railway, so if I have to pull it out for any reason, it's a real pain.

[docdrs]

Hey after watching that video I'm thinking about doing that to my prop. Does anyone know if the oem props are lapped on a new boat? I'm all about doing things properly , just trying to figure out how I can do this on my boat lift without losing a finger or hand

[CJD]

We dinged the old prop yesterday and bought a new one, so i got a chance to deal with this issue. The dealer recommended torquing to 50 ft/lbs.

I was expecting the lapping to take a while, but it turned out the prop fit perfectly after just a minute spinning it on the shaft. I was ready to lock the shaft with vice grips, but there was enough resistance to just spin the prop and the shaft stayed stationary. I got a perfect fit along the entire contact surface. After reading several posts of loosing props, I was concerned that my prop may not have been fit properly. I was glad to see that it was installed correctly at skier's choice.

To be clear about taper joints...the taper holds the prop in place. If the taper is lapped properly, the key is extraneous and does nothing for us. If the prop ever gets loose, from improper fit or hitting something under power, then the key will not last very long, but it should get you home to fix it. The cotter key is also extraneous, but it should hold all the parts on the shaft, again, long enough to get you home.

[SquamInboards]

I lost my prop because it wasn't properly fitted, and I didn't notice the cotter pin was missing. So when I shelled out for a new 541, I wanted to keep it, and that's how I learned about lap fitting. I also took the opportunity to pull the shaft and die check it, so I was able to do the lap fitting with a rig to spin the shaft with a drill. I started doing it by hand, but it was taking forever, so I rigged something up so I could put the prop on the floor and spin it with a drill. It worked so well I actually went too far, but no harm done. If I was going to do it on the boat, I'd either rig something up to spin the shaft or the prop.

There are a couple of really good reasons to properly fit a prop, not loosing it is one, but the other one that is more important, is that your prop should not rely on the key to drive the prop. If the prop is just a little loose, it'll bang on the key, and this can lead to the shaft breaking. Apparently most shaft breakage occurs at the keyway for this reason. What many people don't know (I didn't) is that it's the fit that drives the prop, not the key. The key is there for safety in case the prop gets loose.
I don't want to spread any paranoia but that's also why it's generally recommended to replace the shaft coupler with a new one any time you remove it from the shaft. Cheap insurance against failure at that end as well.


It may be overkill to do the heating thing, but I'd rather be swearing and banging and heating when I finally need to get the prop off, then swearing and sweating and paddling to get my boat back to the dock with my prized 541 on the bottom of the lake. My boat stays in all season, and my dock is my railway, so if I have to pull it out for any reason, it's a real pain.

^^ Well said.