I have the Tunder Tiger 91Four stroke engine and need to install a spinner but will have to
use the one nut that comes with the spinner instead of the two nuts that come stock with the
TT.91. Do these nuts that use tention against each other have to be used or will the one
spinner - longer nut work just as well. The Shaft on the TT91 with a MA 14x6 is not long enough to hold
the two stock nuts and the spinner nut as well.

Basil,

I believe the standard nut and lock-nut must be used, to prevent the prop from ever being thrown, in an event of a back-fire. Most four-strokes will have a long enough shaft thread, to also allow the spinner nut.

After tightening the standard prop nuts securely, the spinner nut does not have to be tightened very strongly, since it is merely used as a go-between, for the spinner cone bolt to thread into.

But don't just loosely fit it. Tighten, but do not "gorilla" it, on the shaft's remaining threads.

So yes, you may have three nuts on the shaft.

The question is not entirely clear, so I'll go over 3 scenarios:

1. Plastic spinner
Just use the standard lock nut arrangement. If the spinner is large enough, the spinner cone should just snap/screw on as usual.

2. Aluminium Spinner
You must get the correct spinner adapter for your engine. A 4 stroke spinner adapter will include a lock nut arrangement. The spinner cone screw will screw into the face of the lock nut. Frequently, the spinner cone bolt will need to be cut down depending on the size of the spinner and thus the distance between the lock nut and the tip of the spinner cone.

3. Prop nut.
I have used a Harry Higley prop nut on my OS FS70 4 stroke. HH also makes a 'lite lock'. This is just a nut of the same diameter as the actual prop nut. Screw the lite lock on first and then the prop nut.

Don't use plastic spinners with a four stroke. I've tried using the Higley light lock and Dubro spinner nut combo, but I found it was not safe especially if an electric starter is used (it loosens the spinner nut). A double jam nut is needed and after tightening the first nut, I tighten the jam nut against the first nut using separate wrench on each nut. You could get the Vortech spinners and jam nut kit from Dave Brown, which is cheaper than Tru-Turn.

Here's an interesting way to modify the spinner nut for 4C engines, although I have not tried it myself :

http://members.cox.net/bdfelice/Spinner/spinner.htm

I was able to get a case hardened 5/16th nut that will fit first before the Aluminum spinners nut. That way there will be a two nut setup
is this enough to do the job. One goes on tight and the other one over it. Ithink this is simular to the Harry Higly setup.

I have thrown props with the Higley and spinner nut setup. The double jam nut is safer. Ask me how I know.........

From looking at the stock 2-nut setup that came with the engine, the second nut, as it tightens inside of the conical hole in the first nut gets squeezed on the shaft, giving it more of a locking effect than just the side by side locking nut setup. But how about using Locktite on the Harry Higly type setup will that make the difference?

Basil, I don't use Loctite as I put my prop on at the field, due to space constraint in my car. But you could evaluate it. I've seen some people use nail varnish from the wife as it dries faster.

Gluing a disc of medium sandpaper to the front of the prop drive washer sometimes helps a lot.

Bill.

standard nut + spinnet nut + proper tightening = adequate protection against throw prop. The triple nut setup works, of course, but really not necessary.

If the backfire is strong enough to loosen a pair of nuts tightened against each other, it will surely loosen any of the two nuts in the triple setup. Think about it, you can have 20 jam nut in series, how does the last two nuts know they are butting up against another nut or the prop washer?

If you've taken Static Mechanics I and know how to draw a free body diragram, you can figure that out in a jiffy.

Not true with my Saito 100, especially with an electric starter. I am using a Tru-Turn setup now with good results

great planes makes spinner adapter kits, i found them at my lhs. it replaces the stock set with a locking set that has the spinner adapter. http://www.greatplanes.com/accys/gpmq4550.html
look at the adapters under the spinners.

part# GPMQ4588 Adapter Kit-O.S. FS70-120; 140RX is 5/16 -24

Hi!
You certainly don't need a lock-nut on any engine....!
But always use a good quality alu spinner like Tru-Turn .... I always put a thin round, 0,4mm plywood spacer behind the rearplate on the spinner to prevent the plate from slipping when tightening the spinner nut.
I've Never had a spinner or prop come loose.
Regards!
Jan K

I have the same problem with the TT91FS, I need a shaft extentsion otherwise there is not enough threads for the 2 lock nuts +spinner nut.
Its to bad TT has to cut corners that way. I can use the spinner nut by itself but feel better with 2 locking nuts.
David

here is a picture of the great planes locknut with spinner adapter built in.

Well, lots of time on the Lite Lock and spinner nut. Lots of Backfires, never a loose nut. Saito .91 and .72. But that's just me.

Never lost a nut either... however, I have lost a plastic spinner or two.

Here is the Tru-Turn part # for the TT .91 adapter, it replaces the stock outer jam nut and costs $8.39. TT-0523-A