Drmeff

What is the proper prop nut for at 3/16" shaft?

10-24 or 4-40?

I am trying to get a few of them off of funrcboats because my local hardware store had nothing that fit (go figure) but their site does not specify which one is for which shaft. I am using the driveshaft that they sell (the 18" 3/16 shaft with welded stub).

jetpack

My Feedback: (1)

All 3/16" propshafts are threaded 10-32's. Unified National Fine class. A store bought safety nut will be large past the diameter of the prop hub across its corners. The prop nuts are threaded 10-32 but are a flange style nut, which brings the hex head size down from a standard 3/8" hex. A standard nut will work, it just won't look as slick as a flange nut, where the outside of the flange itself measures 3/8" and the hex sits inside it.

toyotatruckin

use a regular nut and put a piece of fuel tubing between the prop and nut itself does two things ...1 serves as a cushin 2 the nut wont back off i havent had any problems doing it this way

jetpack

My Feedback: (1)

When working your props, get rid of the raised prop number thats casted on the back, and pencil engrave it on the hub length if you need to keep track of the number of it.

I had prop hubs wear out, because the shoulder diameter on the stub shaft only covers half the prop hub length, and the thread diameter is way smaller than .187".

Soon as I noticed my props getting wobbly as I slid them onto the shoulder up to the drive dog, I quit using the fuel line cushion and running the prop straight up tight and solid to the drive dog with the locknut. The nut stays tight because it beds completely flat and snug to the back of the prop without them raised numbers to wear down and loosen it. That is why K/B uses those cushions, so people don't get all upset when them numbers wear off and the prop always comes back loose. That rubber cusion only induces prop shake and wear to everything involved in my opinion. Good for K/B's pocket, but not mine.

If anything, that fuel tubing belongs behind the prop lock nut to keep that from falling off, but I really doubt that has ever happened. The prop will slip off the drive dog before the nut reaches the end of the threads.

Just my two cents, but if you ask me that fuel tubing should never be used back there. Props need to be tight, especially when only half the propshaft shoulder riding inside it. In full scale hydro racing, any kind of prop shake is disaster. Remember, these are surface drive setups, and we usually use two-blade props. A certain recipe for prop shake or bad rotation harmonics. I think many people need to re-think this because I see it everywhere, and will never buy a used prop that uses that setup.

The optimum prop set-up would be to mount the prop tight and solid on the propshaft so it all acts as one piece. Then balance the entire assembly, but can't do it with the stub shaft arrangement.

misshydro

Your not kidding me this this?hardware doesnt have that size? That God mine has and I get the self locking ones too.[8D]

jetpack

My Feedback: (1)

But are they the tastey stainless steel self-locking or the cheapo rusty black alloy ones[sm=wink_smile.gif] or are you fooled by pretty zinc plating??[sm=50_50.gif][sm=tongue_smile.gif]

jetpack

My Feedback: (1)

I just thought I would add that 1/8" propshafts use an uncommon thread size, which is a 5-40.

5-40 threads are designed to fit into a common 1/8" drilled hole with no clearance.

This uncommon thread size combined with the flange-style nut is what helps make Prather prop nuts the only ones that we can find.

Ron Olson

My Feedback: (1)

You're looking in the wrong section of the hobby shop. Team Losi has the 5-40 nylon insert nuts. No flange but they are the right thread.
I use the fuel line trick also. It has more than one purpose. You can use it in case you lose a prop nut and don't have a spare, it also works to keep the prop nut on as it works like a lock nut, especially if you're using a streamlined prop nut and last, it will wqrk as a shock absorber in case the prop hits some debris in the water.
I don't know if they still do or not but K&B outboards used to come with a piece of large fuel line for that purpose already in place.

jetpack

My Feedback: (1)

Thanks Ron,

I'll check into the Losi's. I've searched high and low online with fastener suppliers and I've found it impossible to find a box of the Prather type. There must be a secret factory hidden in NASA somewhere that makes them.

My K/B SS 3.5 came with a stock piece of tubing on the propshaft, and I used it for one season, then left it off because the prop hub length hung over half the thread length, and was not a snug fit on the stub diameter. I started to notice it getting to be a looser fit due to wobble, so I started going without it.

There are benifits to using the tubing like you mentioned, and I would use it if the props fit better. I am thinking of filling/sizing my hubs with putting a stainless stub that is more on size inside the bore, and filling with solder...then balance.

The pilot diameter on the K/B stub shaft seems too short for the prop hub lengths I'm running, and its been causing problems.