Fitting a Prop

[model 10]

Originally Posted by a64pilot

I'm not arguing, but if there is no need, why is it there? I've seen keys that were a little too tall and or not seated properly cause problems as the prevent the bore from properly seating on the taper, so it would seem that if it's not needed, the proper thing would be to not install it.

You can't blame the taper for an ill fitting key. Personally, I would never trust just a taper for the long haul but I do believe the science. I also believe **** happens.

[Ziggy]

Originally Posted by a64pilot

Permatex Anti-Seize Lubricant is a highly refined blend of aluminum, copper and graphite lubricants, for use during assembly to prevent galling, corrosion and seizing, and to assure easier disassembly. Featuring salt, corrosion and moisture resistance, this lubricant is ideal for marine use.

I would recommend against any compound containing graphite. Graphite in salt water has been found to cause galvanic corrosion of stainless steel. I found a thin coat of Tef-gel (PTFE suspension) works well.

[bobconnie]

Very seldom do I agree with Fastbottoms on anything! LOL But he has it right on this one!! Any taper fit with or without a key never needs any Lube of any type !! When you want taper to fit right you have a Good machinist do the fitting, and you sure don't want any interference from lube on this fit !! Do it dry and be sure it's clean before installing it !! Just my 2 cents

[fstbttms]

Originally Posted by bobconnie

Very seldom do I agree with Fastbottoms on anything! LOL But he has it right on this one!! Any taper fit with or without a key never needs any Lube of any type !! When you want taper to fit right you have a Good machinist do the fitting, and you sure don't want any interference from lube on this fit !! Do it dry and be sure it's clean before installing it !! Just my 2 cents

[a64pilot]

I believe I'll either go the Tef-Gel route, or possibly blue Loc-tite. It's not a lube I'm after, it's corrosion prevention and or making it easier to remove the prop after a few years. Maybe it's rare, but I've seen a rosebud acetylene torch used at times to remove props they were stuck on so well

[fstbttms]

Originally Posted by a64pilot

I believe I'll either go the Tef-Gel route, or possibly blue Loc-tite. It's not a lube I'm after, it's corrosion prevention and or making it easier to remove the prop after a few years. Maybe it's rare, but I've seen a rosebud acetylene torch used at times to remove props they were stuck on so well

You are making a mistake. Props are not supposed to be easy to remove. That's why we have special tools to do it. I suspect I've pulled more props than most here, and in twenty years, I've never had one that I couldn't remove.

[Terra Nova]

Originally Posted by fstbttms

You are making a mistake...

This.

[Cheechako]

Originally Posted by Guy

Any machinist who knows about tapers will tell you, with the interference fit on a taper you don't need a nut or a key, unless the prop starts to come loose while you're backing up.

As for an anti-seize compound, it's more important if you have 2 steel parts together, like a stainless prop and a stainless shaft.

Boy... they sure go to a lot of work to put a key slot in shafts for no reason them!

[NoTies]

Originally Posted by Cheechako

Boy... they sure go to a lot of work to put a key slot in shafts for no reason them!

The key on a tapered shaft is generally there to prevent turning of the hub on the shaft during initial tightening, thus preventing possible galling. The are many taper applications that don't use a key and even with a key it is never designed to impart any driving force. Cummins B series engines have keyless tapers driving their injector pumps to allow for timing adjustment.
I love when people wadeinto the argument with comments about aircraft prop shaft tapers.
For a start, they are operating in a different medium and secondly, arcraft prop hubs are by necessity a lot more lightly built and have different requirements.
Use anti seize or lubricant on a marine prop shaft taper at your peril.
Personally, I'll stick to what we've been doing successfully for years and check lapping surfaces, check for key binding, then clean with acetone prior to assembly. Never lost a prop yet on any client's boat.

[four winds]

Why no anti-sieze? Because with a taper fit one wants it to sieze(not gall hence the key). That's how it works. And why it's hard to remove.

If the key was intended to resist the torque, why wouldn't it just be a cylinder fit like the other end of the shaft?

Engines with common crankpin connecting rods are taper fit, often with no key at all.

[four winds]

Here's a well written proceedure, in my opinion.

1- Check key and keyway

Check that the key fits the keyway. Ensure the key slides through the new prop’s keyway without jamming at any point or with no apparent slop. It will be helpful to mark the direction of the key in the keyway.

2- Propeller fit

Dry fit the propeller to the shaft, without the key in place first. Check that the propeller does not rock on the taper. Mark the shaft at the forward end of the propeller hub. This is most is important - to first fit the new prop onto the shaft without the key in place and to mark the shaft at the forward edge of the prop hub. Remove the prop and place the key into the shaft keyway. Slide the prop back onto the shaft and check that the forward edge of the hub comes to your shaft mark. If not then it is likely that the key is too large, and the propeller is not seated to the shaft taper correctly. Remove the prop and file the top of the key down until the prop will slide on to the shaft and reach the mark. This will ensure that the prop is now correctly seated on the shaft taper.

3-Fit propeller to shaft

It is good practice to "lap" the propeller to the shaft. It only takes a few minutes and will improve the fit. Purchase some coarse valve grinding compound from an automotive supply store. Liberally coat the tapered end of the shaft and the bore of the propeller with the grinding paste. Slide the propeller onto the shaft. Apply gentle pressure and rotate the propeller on the shaft 90° to the right , then 90° to the left and repeat this several times. Occasionally remove the propeller from the shaft and wipe out the valve grinding compound and visually inspect the bore. Continue this until a minimum fit of 75% is achieved. Most valve grinding compounds are water soluble and wash off easily with soap and water.

4- Check propeller position

Carefully clean the propeller and the shaft and check the "dry fit" once more. You will probably notice that the propeller goes to a different position on the shaft than before. Mark this new position.

5- Install propeller

Install the propeller with the key fitted to the shaft. Some people prefer to use a lubricant on the shaft, we do not recommend this. Check that the propeller goes up to the mark on the propeller shaft. If it doesn’t, the propeller is sitting on the key and you must reduce the height of the key to overcome this problem. Draw the propeller up the taper using the propeller locking nut, then lock this nut with the second nut. Don't forget to fit a new cotter pin.

[four winds]

And just for the sake of debate. Here's a step from another write-up.

Next, lightly coat the shaft taper and key with low- viscosity oil, such as automatic transmission fluid. Never use grease on a propeller bore or shaft taper. A light lubricant is meant to ensure that the propeller fully engages the taper and key without binding. The lubricant is not meant to aid disassembly. In fact, many prop shops frown upon the idea of using any lubricant on a taper, no matter how light or little. Applying grease to a taper or bore may, in fact, prevent full engagement of the prop. Because it is highly viscous, and a liquid of sorts, it’s possible that the grease may hydrolock the propeller, preventing it from fully engaging the shaft taper. The bottom line is that you want the propeller to become well and truly stuck on the shaft taper. You, or someone else, can worry about removing it later.

[Exile]

Recently I had an experienced diver remove my prop for re-pitching. After reading this thread, I think I'm finally understanding why he declined to reinstall the prop with the boat in the water. Although I had this done once, it doesn't sound like the greatest idea. Maybe fastbttms or another one of the pros can comment.

[a64pilot]

My intent was to try to ensure it didn't seize, so that I could get it off in the water if I had too.
If you look at the size of the shaft and the length of the prop that engages the shaft, especially if it's lapped, well that area is huge when compared to the engine HP and prop RPM, can't see how anti-seize could cause a spun prop with that large an area, unless the prop wasn't properly torqued.
I'll try a novel approach, I'll ask the prop manufacturer.

[a64pilot]

BTW, what is the correct torque for a prop? I know it varies according to shaft size, but so far I haven't found anything at all, just German torque it.