ptuxbury

Hello folks,

I spent quite a bit of time searching for help on this on a couple of different message boards, but didn't come up with anything. I have a Magnum 91 4-stroke engine that I want to fit a 1" Tru-turn prop hub on for a Corsair I'm putting together. When I used the Tru-turn prop adapter online tool, it said I needed a TT-0522-A prop adapter. I was supposed to use my normal prop nut, and use this adapter as a replacement for the jam nut on my engine. The problem is that when I cinch the jam nut down all the way, the prop hub bottoms out on the top of the jam nut before it bottoms out on the prop washer, creating a gap between my prop hub and the prop washer (see image "PROP GAP".

I called up Tru-turn, and they asked me what engine I was using. I said "Magnum 91 4-stroke" and they said that this was the problem. The TT-0522-A prop adapter isn't meant for the Magnum 91 4-stroke. This bothered me a little because the online prop adapter selection tool led me to that part number. They recommended TT-0523-A (prop jam nut adapter), but said that it needed to be used with TT-0523-AB (prop washer and nut). The TT-0523-AB is meant to replace the prop washer and nut that came with the engine.

I received these parts yesterday, and I can't figure out what I'm supposed to do. The TT-0523-A jam nut adapter is a little bit shorter than the original TT-0522-A I had purchased, so I can see how that will allow the prop hub to bottom against the prop washer, but the crankshaft thread is so long that the jam nut adapter does not bottom against the prop nut. The only way I can get this to work is if I remove about 3 threads off the crankshaft thread with a dremel (are there any issues with me doing this?).

I also cannot see how the TT-0523-AB (prop washer & nut) is of any value to me. It is basically the same thing as my prop washer and nut, except the diameter of the washer is much smaller (smaller than the prop hub even), which seems bad to me.

I'm not quite sure what to do, but I think I'm going to send the TT-0522-A prop jam nut adapter back, along with the TT-0523-AB prop washer and nut, and then cut some of the threads off the end of the crankshaft. I just don't want to send something back, and then realize I needed it, incurring more shipping fees than I've already paid.

I've also attached a picture of the engine as it came with stock prop washer, nut, and jam nut, and the three prop adapters, TT-0522-A (longer), TT-0523-A (shorter), and TT-0523-AB (possibly useless prop washer and nut).

I have two more quick questions. Can anyone tell me what the aluminum spacers that came with the adapters are for, and can anyone tell me what the black washer that came with the prop hub is for?

Any help would be greatly appreciated.

Thanks,
Tux

alan0899

G'day Tux,
The prop adaptors you have there are for spinners, not prop nuts.
If I were doing this I would use the washer, then main nut, then jamn nut & then the prop hub, It's only for looks anyway, & the prop won't come loose.

silver.kiwi

TUX:
From your photo showing the "gap", it appears that the original jam nut has been replaced with the scale prop hub leaving the slight gap? Allan's advice (above) will work but might leave more clutter showing than you would want. You might try just cinching down the original prop "nut" extra tight and living with the slight gap you show. I would. If you have the prop "hub" down good and tight also, I doubt the prop is going to do anything. Should it break free during a backfire, it will be stopped by the hub and only spin free on the shaft. All of this is based on my assumption that the rear of the TT prop hub is drilled out so that it covers the prop nut when it is screwed down on the shaft. I could not tell from the photos. Allan from down under is correct about the small shims/spacers and adapters. They are for spinners with differing diameter shaft holes and lengths. Send the rest back or save for another project.

Flyboy Dave

My Feedback: (21)

Those prop adapters are to be use when the prop shaft is too short, not too long. There are
three different sizes you have, depending on the "reach" you need. The big black washer is
used in the normal fashion between the nuts and the prop. The end with the small threaded
hole can be used to secure a spinner. The prop would have to be drilled to a much larger hole
in the center to use those adapters. Hang on to those nuts, you may need them some day,
and they can be hard to find.

The small washers are adapters to be used if the hole in the spinner or prop is too big for
the shaft on the engine you are using. They are different thicknesses, so you can select the one
that adapts the prop or spinner to the shaft. Hang on to those too.

All you need is another washer between the new nut you have, and the prop. Generally a
washer is used between the prop nut and prop, but it is not absolutely mandatory. It depends
on how many threads you have to work with. Do not cut the threads off the engine, use a washer.
You may need all those threads in another application if you want to use a spinner.

If you need further clarification, just ask.

FBD.

ChrisAttebery

My Feedback: (15)

Take a look at the image below. Your setup is in the top left corner. I could be wrong here, but to me it looks like you need to ditch the stock prop washer.

Install in this order:
1. The large washer that came with the hub.
2. The heavy black washer 523-AB.
3. The prop nut 523-AB.
4. The jam nut 523- A.
5. The hub itself.

You may need to use one of the small sleeves to center the hub adapter's washer 523-AB. Give that a shot and let us know what happens.

If it doesn't work that way call Tru-Turn and ask for technical support.


Chris

carrellh

I think you're going to have to cut the end of the crank. Put a nut on it first to cleanup the threads when you remove it after cutting.

Magnum .91 four strokes are strange beasts. I got one for my 4*60 and the crank was so short that the jam nut wouldn't go on if the spinner backplate was installed. I wanted to use a spinner and had not seen this issue before. My brother had three of them new in box after the last big sale so we pulled them out to check the shaft length. One of his had a short shaft, like mine, and the other two were "much" longer. He doesn't like spinners on most planes so we swapped engines.

I suspect you simply got one with an extra long shaft.

I have to guess they have multiple suppliers for cranks and you get whatever they're using on a given day.

w8ye

My Feedback: (16)

Yes on the cranks. I've seen some strange dimensions on some ASP/Magnum parts, especially when you buy replacement parts.

ptuxbury

Thanks for all of the suggestions. Here's what I did:

After my initial posting, I realized that the prop nut that came with TT-0523-AB not only fit the small black washer it came with, but also the large black washer that fits in the counterbore of the 1" prop hub. This larger washer was the same diameter as the original prop washer that came with the engine, so it was a good replacement for it.

So, I put the washer that came with the prop hub and cinched it down with the prop nut that came with TT-0523-AB. Then I put the jam nut that came with TT-0523-A on, but it bottomed on the threads of the crankshaft before it bottomed on the prop nut. At that point I measured all the parts up and realized that I needed to remove approximately 0.150" off the end of the crankshaft for everything to fit. I did this with a dremmel, and the prop hub seated beautifully on the prop washer.

I've included a couple of pictures to illustrate. Sorry they look so bad, but I'm at work, and all I had was my cell phone to take the pictures with.

Again, thanks for all the advice.

-Tux

carrellh

Looks perfect! Good deal!