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Old 12-05-2015, 12:17   #16
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Re: JB weld on ss prop shaft

Someone mentioned corrosion beneath the JB Weld. That stuff is epoxy, so unless you get air bubbles in it, corrosion will probably not be a problem. However, I would worry about crevice corrosion with a Helicoil in the hole. If the Helicoil itself doesn't rust away.

The original hole would have already weakened the shaft a little bit. Drilling the hole out bigger to re-tap it means you've removed more metal from an already weakened shaft. Probably be OK, might not.

Weld it up and redrill seems like the right way to do it. Just because one does not want to do something the right way, doesn't mean that doing it wrong is somehow OK.

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Old 12-05-2015, 12:58   #17
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Re: JB weld on ss prop shaft

FatBear, in my opinion corrosion will not be a problem with a Helicoil if Loctite is used on the coil and the bolt. That will insulate them both from the SS shaft. Also it is normal practice to use a zinc anode on the shaft and / or the prop. After all the prop is usually made of bronze and I don't think you worry about it corroding with a working anode. The amount of metal removed for a Helicoil is very small and in an unstressed part of the shaft. It's not going to fall off. Helicoils were used in aircraft, at least when I used to work on them.

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Old 12-05-2015, 14:28   #18
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Re: JB weld on ss prop shaft

I'm for doing it right. Worth it in the long run. Remove the shaft. Have it taken to a machine shop that has the equipment to do it (not all do) The shaft may have to be heated and then the hole completely filled in with identical metal. MIG under the proper settings may do it. Even then it will not be as strong as the original metal.
Then drill in a different location and drill it correctly with the right thread. Place the prop on the shaft and make sure everything fits perfectly before leaving the shop. Replace shaft and propeller.
There, wasn't that easy?
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Old 12-05-2015, 15:41   #19
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Re: JB weld on ss prop shaft

Here is what we know:
1. Where the original screw was, the threads are stripped.
2. The hole isn't straight.
3. The owner does't want to remove the shaft.
Here is what we don't know:
1. Was the original hole straight?
2. Is the non-concentricity of the hole to the shaft caused by it not being drilled correctly in the first place?
3. Is the non-concentricity of the hole to shaft only at the end of the shaft caused by a harder bolt working the metal?
4. What is the diameter of the shaft relative to that of the bolt?
5. What makes it so difficult to remove the shaft?
Solutions as posted by me and others:
1. Drill and tap hole to next larger size bolt.
2. Drill and tap for a spring type helicoil.
3. Drill and tap for a Time-Sert.
4. Remove shaft, weld and redrill hole.
Obviously, to do the job right, solution number 4 is the best, especially so since the shaft can be put in a lathe and the hole drilled and tapped true.
Solutions 2 and 3 are worse than solution 1 since the helicoil and the Time-Sert still require that a hole be drilled and tapped, then a threaded insert installed to take the original size bolt. Why not just use a larger bolt and skip the Helicoil or Time-Sert? What am I missing? Why are two threaded objects required to secure one bolt?
Furthermore, a helicoil or Time-Sert would be recommended if the threaded area had to meet a specific size, like a spark plug. However, in this case, we don't seem to need that.
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Old 13-05-2015, 21:32   #20
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Re: JB weld on ss prop shaft

I would suggest that the next size lock bolt would require a much larger hole than a helicoil would. Think 6 mm or 1/4" lock bolt. Next size up is 8 mm or 5/16". Helicoils have their own special tap and drill in a kit. The tap for a 6 mm helicoil might be 7 mm though I haven't measured it. Its much less a hole than a 8 mm bolt requires. The lock bolt most likely presses on a special washer which presses on the prop retaining nut so best to keep the bolt the same. I'm just guessing it's a 6 mm or 1/4" bolt. Welding can introduce distortion which is not desirable in a prop shaft. Helicoils are GOOD engineering practice.

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