My TF Mustang has a Homelite 45 cc converted chainsaw motor. It has the typical tru turn type parabolic spinner with bolt on the front attaching it to the shaft. I am having trouble with the prop moving no matter how much I tighten it down. Could there be play in the prop hub? I know it it tight on the motor, but instead of a bolt to hold the prop on, I use a piece of steel all thread. I place the spinner base on the prop hub, then the wood prop, then the washer, then the tru turn adapter. I tighten this adapter to the steel thread, put on the parabolic spinner and then tighten the allen bolt to the tru turn adapter. After running the engine, the wood prop has indentations from the parabolic spinner. I've thought of drilling out the washer and prop hub and adding split pins. Any thoughts?

No, don't add split pins. That is unsafe. If the prop loosens up, the pins can damage the prop, and then it can disintegrate while running.

If I am understanding what you're doing, it may be the all thread. All thread is not very strong, and could easily be stretching and losing it's tension. You need to use at least a Grade 5 bolt. Tighten the prop, and then re-tighten it after sitting overnight. Another thing that could be happening is that your spinner adapter nut might be bottoming out and not allowing you to actually get the prop tight. If the spinner has damaged the prop, you need to replace the prop!

I don't like to use bolts for my props as you are wearing the aluminum threads each time you change the prop. I use long Grade 5 bolts to make my own "all thread". I clamp the head in a vise and tap the whole length of the bolt. Then I cut the bolt at the desired length. This gives a nice strong stud that I then install into the prop hub with Loctite. You can even drill the end of the stud for your spinner bolt if desired, but that should be done on a lathe.

(Note that to do this, you need to use a Grade 5 bolt that doesn't have a shank that is too large. If the shank is too large, you will need to turn it down to the proper size on a lathe before tapping the shank part.)

AV8TOR

av8tor is correct in every part of his post.
Is it definitely the prop that is coming loose on the hub or is it the spinner cone coming loose?

You state it is a "tru turn type" spinner. I have seen many of the lesser brands of those where the spinner back plate is "not worth a toss" and the spinner itself is the cause of exactly the problems you are seeing.

Try taking the spinner off altogether (Including the backplate), Replace the prop and use a felt tip pen to mark a line across the hub of the engne and the prop hub. Fly the plane then when it has landed - see if the line is still lined up.

if it is still lined up - pick up the spinner, Place it on a sound surface (not your dining table - you will get in trouble) then smash it to pieces with a large hammer - then place said pieces in the bin and go get a better spinner

Both great answers! It is a Dave Brown Spinner. I also thought the spinner itself may be sliding because I use a dynatron starter. Perhaps there is a large spinner that won't require the bolt in the center. If so, I can just use the bolt that came with the prop hub. I also should have thought about making a reference line to see what is moving. I'll make a few marks, run the motor and see if I can figure out what is going on.

I was having trouble with a prop not staying put on the back plate.....big engine/big prop. It was actually chewing at the wood. My knurling is finer than I would like. Normally the engine should tighten the prop nut. With a starter you are working against that. I put rosin, like for violin bows and baseball players, on the hub. No more slipping.

I am not sure this will be of help.

BTW rosin is what gunsmiths use on rifle barrels to keep them from slipping during removal and installation. With fitted maple blocks and a hydrolic press you can put big weight on a long cheater bar and not have it slip. It does not mess up the blueing either.

I have used the sandpaper washer trick a couple times.

I cut a washer that fits the face of the prop hub out of sand paper and put it beind the prop or spinner (wherever it is slipping), once I used sticky back sandpaper and glued it to the face of the prop hub.

Nowdays I have a mill and lathe, so I tend to machine or knurl marks in the prop hubs to prevent slippage.

When tightening the prop, tighten the first nut and then hold it with a wrench (to prevent it turning) while tightening the second. red

Ditto Av8or:- Allthread is very soft and you can't tighten it properly. 8.8 or 10.9 grade (metric) you can torque down properly.

On the waterpump fixing bolts for my TR4A I used an exhaust manifold stud to replace one bolt that was almost impossible to get in. I then used a nut to secure the pump instead of the bolt. Why not use a stud like this (metric studs are available) for fixing the prop instead of modifying a bolt?

Sincerely, Richard