30s/40s Franklin restoration, prop stuck on

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Anthony Samuel

Filing Flight Plan
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SamsExplosives
77DF4FA0-CCF9-49B1-88CC-1FB02EE67EFD.jpeg 7A12E7DA-31C8-40CE-BB62-6D9EE233020C.jpeg D452CC49-2128-4FB2-87CA-D097596525D6.jpeg I just inherited this Franklin 4ac-176b2 and look forward to restoring it, however, one primary issue hindering this task is the prop is stuck on it. I’m assuming the rust has ‘welded’ the wood to the metal on the bolts because it’s not even budging.
I’m wondering if there is any way to safety remove the prop without causing damage? Any tips/tricks?
 

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What is on the back of the prop? Is it a metal flange that stays with the prop? It would really be a shame to destroy that peop.
 
That is a difficult one. If the studs have threads that extend deeper than the exposed bit and the wood has shifted/expanded (via moisture)/etc the wood could have thread-shaped grooves molded into it that would make removal quite difficult without a lot of force. Applying enough heat to the bolts to char the wood would work, but that could damage the bolts as well as the prop. Shrinking the wood is perhaps an option, and could be accomplished be either building a tent around the engine and using a dehumidifier and heater inside the tent to really dry out the wood. That could cause some localized checking of the wooden propeller as well, however and could be prevented by protecting the prop with waterproof/vaporproof coverings other than the hub area and sanding the coating off the hub area to allow it to selectively dry faster. Whether that is actually a good idea for a wooden prop, I don't know, but I work with wood for a living, just not in prop form.

PB Blaster is always an option.....
 
Are they bolts or studs? If bolts, you should be able to either tap the bolts with a soft hammer, or turn them to break them loose. But the big issue is likely the tight fit of the prop on the center. Sometimes it takes a lot of working back and forth to get it off.
 
If they're bolts, and there's some room between their heads and the crankcase, I would "tap" them, like Dana says, but I would use a rivet gun with a piece of brass between a countersunk rivet snap (flat head) and the end of the stud. Sometimes rapid tapping will move stuff that doesn't want to move. I have dislodged numerous frozen bolts like that.

But one hates to introduce much shock into a crankshaft. It's a last-ditch effort.

If they are studs that are threaded into the hub, I would double-nut the outer end, jam the nuts tight together, and try to turn the stud out.

If it's frozen onto the hub pilot, you might have to sacrifice the prop by chipping it off.
 
Dry ice, or CO2 fire extinguisher or, even better, liquid nitrogen, will shrink metal a lot more than wood.
Is the hub of the prop bigger than the hub on the crankshaft? Can you make a plate to go behind the prop and fabracobble a "puller"?
I would definitely consider Mr. Thomas' suggestions.
 
They’re studs, not bolts, apologies for confusion. Essentially it’s to the point the prop SHOULD slide right off, it just won’t which is why I think it rust welded (is that a term?) the studs to the wood.
I appreciate all the help though! Y’all have given a lot of ideas. I’ll just have to convince a buddy via a pack of beer to accompany me next when I go retrieve it and spend a few hours screwin with it to prevent anger-induced damage haha. I doused it in WD-40 before I left, hopefully that did something. Next I’ll go the next step with that rigged puller idea.

or maybe I’ll just start it and launch the prop into orbit.
 
Anthony Samuel said:
They’re studs, not bolts, apologies for confusion. Essentially it’s to the point the prop SHOULD slide right off, it just won’t which is why I think it rust welded (is that a term?) the studs to the wood.
I appreciate all the help though! Y’all have given a lot of ideas. I’ll just have to convince a buddy via a pack of beer to accompany me next when I go retrieve it and spend a few hours screwin with it to prevent anger-induced damage haha. I doused it in WD-40 before I left, hopefully that did something. Next I’ll go the next step with that rigged puller idea.

or maybe I’ll just start it and launch the prop into orbit.
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Kano kroil works better than WD
 
Restore to display or fly?

At one time bearings were unobtainium.
 
dtuuri said:
If I'm looking at it right it'll push the engine not fly off the studs. Did it come off a swamp boat? Gano propeller, who they?
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Was originally a STOL engine then on an airboat. Any form of a log book is long gone unfortunately
 
Magman said:
Restore to display or fly?

At one time bearings were unobtainium.
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Display for the time being, I have a decent collection of antique things and this would be great for it. Maybe someday I’d toss it in a single person STOL but that might as well be light years down the road
 
Ok, the guy I know who has worked on engines like this basically said what others have said here, he recommended PB blaster, I'd give that a few days of repeat treatment. He also said to drill the studs out and use an extractor (screw it out), I've asked to clarify if he knew if the studs were screwed into the backing plate or pressed. Either way though, if it comes to that, drilling is probably the best bet IMO to minimize damage. If they are pressed in, what I would do is drill through, if they are pressed in, and increase the drill to a diameter where studs will pull out.

Edit, I'd give Franklin engines a call and see what they say.
 
If that hub pilot is seized in the prop bore, drilling out the studs will do nothing.

Putting liquid of any sort on the wood will swell it and make it hold even tighter.

The steel rusts inside the wood. When I restored my Jodel I found plenty of that after only 20 years. Whatever plating is on the bolts and crank flange is sacrificed to protect the steel, and once it's gone the steel corrodes and the corrosion byproducts accumulate and increase the diameter of the stud or bolt or whatever, and make it tighter. It also accelerates the decay of the wood, so that prop is likely unserviceable anyway. In any case, it looks old enough that the glues in it are likely shot and you wouldn't want to fly it.

If it was me I'd be cutting some steel and welding up a special one-time prop puller for it. Even then I'd be watching for crank flange distortion.
 
One last ditch possibility is something that I did to remove a stuck part (though not a prop!) I took a high-quality hole saw (annular cutter, actually) and removed the "set" on the inside, so that it would slide over the bolt. Then I 'peck drilled' with the cutter sliding on the bolt until it got deep enough. I did this with an aluminum part with a steel bolt, and just put a sleeve in the hole. But at least you'd have a display prop that looked good!
 
Dan Thomas said:
The steel rusts inside the wood. When I restored my Jodel I found plenty of that after only 20 years. Whatever plating is on the bolts and crank flange is sacrificed to protect the steel, and once it's gone the steel corrodes and the corrosion byproducts accumulate and increase the diameter of the stud or bolt or whatever, and make it tighter.
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The forward turtledeck of my all-wood Fly Baby is held in place with bolts through wood. Here's what one looked like after ~20 years of contact with the wood.
corrosion bolt.jpg
It, and the other 11 doing the same job, were a wee bit tough to remove. The builder of my airplane seems to have done a pretty good job, so I suspect he had varnished in the inside of the bolt holes.

Ron Wanttaja
 
I would start off with the least damage methods and work my way up. One thing I would try pretty early on is a torch, heat all the steel up, figure a way to protect the prop if you are trying to save it. Hopefully the last time it was put on it was prepped, maybe with grease? Anyway, whatever there will have hardened over the years, heating it might soften it and make it easier to get off.
 
Dan Thomas said:
Putting liquid of any sort on the wood will swell it and make it hold even tighter.
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Yeah, but wood shrinks when dried out so won't that make the holes smaller? If you can rehumidify the wood without adding to the corrosion it might make the entire prop bigger with bigger holes, no?
 
dtuuri said:
Yeah, but wood shrinks when dried out so won't that make the holes smaller? If you can rehumidify the wood without adding to the corrosion it might make the entire prop bigger with bigger holes, no?
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Nope. The wood will not enlarge overall as metal would do when it's heated. The wood will swell in whatever directions it can, including inward on the holes.

That way I see it: if the OP wants to save the engine without doing damage to it, he might have to sacrifice that prop, which is a pusher prop anyway and not likely to do any airplane it might fit any good at all.

I wish I knew how those studs were attached to the crank flange. If they're threaded in I'd be trying the double-nut idea to try to back them out. Failing that, I'd weld a steel bar to one and work it back and forth to loosen it and back it out. Same thing for the rest, one at a time. The heat will loosen the crust in the bolt bores as well, maybe charring the prop, but the prop, as I see it, is little more than a decoration at this point.
 
Dan Thomas said:
Nope. The wood will not enlarge overall as metal would do when it's heated. The wood will swell in whatever directions it can, including inward on the holes.
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Well, you might want to take a look at this report, see Figure #6. It looks like the bolt holes will shrink in diameter perpendicular to the blades and stay the same in the direction of the tips. Plus, the center of the resulting ellipse moves toward the center of the hub.


I'd bag the blades in wet blankets for a few days and try pulling again.
 
A core drill might do it. I don't know if you can buy one that size, but you could improvise. Take a piece of steel tubing that just slips over the studs, and grind or file some teeth in one end. Then chuck it up in a drill, slip it over the stud, and cut. You'll have to back out frequently to clear the sawdust out. It might mess up the stud threads a bit, and of course it'll oversize the holes in the prop, but it'll save it as a display piece.

Then it still may be stuck on the crankshaft, but that might be easier to work off.
 
Dana said:
Then it still may be stuck on the crankshaft, but that might be easier to work off.
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My Jodel's wooden prop is a tight fit on the hub pilot. Even with all six bolts out it's a fight to get it off. And it's not shrunken with age or affected by corrosion.
 
One more thought which works great for metal to metal (far, far better than PB Blaster, btw) and I used this trick twice just last night on my rear trailing arm... Heat up the bolts with a hot air gun for a couple minutes and touch a wax candle to the thread joint, then heat a bit longer. The wax flows right in as if it were invited and the parts come apart with ease. On metal, no idea about wood. I'd try it though, after I wrapped the blades in plastic and a wet blanket for a few days. :)
 
How about a bottle jack? Wrap a web strap around each blade, put the bottle jack on the end of the crankshaft and pump away.
 
dtuuri said:
One more thought which works great for metal to metal (far, far better than PB Blaster, btw) and I used this trick twice just last night on my rear trailing arm... Heat up the bolts with a hot air gun for a couple minutes and touch a wax candle to the thread joint, then heat a bit longer. The wax flows right in as if it were invited and the parts come apart with ease. On metal, no idea about wood. I'd try it though, after I wrapped the blades in plastic and a wet blanket for a few days. :)
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I’m going to try that! If ya think about it is taking the principle we learned about when learning to sweat a pipe for it to draw in the solder….

I’ve tried the concept with pbblaster but it burns off too easy- I will definitely try the candle idea!
 
PB Blaster..several applications over a period of several days if necessary. If all else fails, a hole saw just larger than the bolts and stop before getting close to flange.
 
Doug Reid said:
PB Blaster..several applications over a period of several days...
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I'm tellin' ya, skip the PB and go straight to the candle and heat gun. You won't get in your eyes, either. Here's a guy using a torch which makes no sense to me since you only need to melt wax:

 
I like the idea of fabricating a puller, spraying some cold on the bolts and some thumps with a dead blow hammer. That canned air for blowing off keyboards and such is a pretty effective cold shot. If that won't get it, alternate hot and cold. There is a a product for freezing IC's and electronic components on the board that works well too.
 
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