Flex Size issues

[modified21]

I thought I had this figured out but I am still confused. I have what I thought was a .187 flex and worked out on here that it was a .150 flex. Well I ordered a new coupler and it is of course the wrong size and there is a significant size variation so I am back to figuring this out. The problem is I DO have a .187 flex (its actually about .006 smaller) and it fits a 7/32 stuffing tube with out the liner. The fit is good its not tight but does run with very little clearance with 1/4 tube there seems to be a lot of excess clearance. Everything I read contradicts this but from what I see it seems to be ok. Do I need to go up a size or am I good with the fit? Thanks for all the help guys still new to this.


Flex Measured.jpgFlex Fit.jpgCollet Sizes.jpg

[longballlumber]

the actual OD of the flex itself will be slightly under .187 and yes you want to run a 1/4 brass stuffing tube (no liner) for a .187 shaft...

Later,
Mike

[modified21]

The second picture shows the fit difference between 7/32 and 1/4. Is the 1/4 fit correct? Just looks odd to me.

[Fluid]

You have been given the correct answer, no need to ask the same question twice.

The tubing will compress slightly when bent, causing a bind. You need clearance, and 1/4" OD tubing is perfect.



.

[LarrysDrifter]

1/4" stuffing tube is correct for .187 flex with no teflon.

[modified21]

LOL... Thanks just wanted to be sure just going to stick this thing in the boat and just wanted to be sure. Thanks for the answer guys. Time to put my insanity to rest.

[JIM MARCUM]

But I prefer using seamless Stainless Steel w/o teflon liners for my stuffing tubes. They're thicker walled & will probably last longer than your boat. As always, relube the flex drive after each days running. JIM

[modified21]

Are you using a tubing bender for brake lines as I have seen SS tube but it looks crazy hard to bend

[JIM MARCUM]

No, I buy 20' lengths of SS tubing from a local tubing supplier & cut it in three pieces to fit in my Kia Soul. Brake line tubing is too thin walled for me. Once you cut a piece for your stuffing tube it's not all that hard to SLOWLY start the bend about 2" from one end by holding the tube with both hands & GENTLY pushing down with both thumbs until you get a SLIGHT bend. Move up an inch or two and bend SLIGHTLY again. Check how the tube aligns between the prop shaft and motor shaft after EACH bend. It usually takes me 3-4 small bends before it's at the right angle.

DON'T overbend it! It's a bitch to "unbend a SS tube without getting a flat spot in the curve. While it's a little harder to bend a tube for a 1/4" flex shaft vice a 3/16", it's not really that hard to do with a little pratice. I have tried 3 different styles of tubing bender, and none worked - usually over bending the tube or getting flat spots is the curve. JIM

[longballlumber]

I have seen Nitro boats that were 10+ years old with A LOT of run time... Not once have I seen or heard anyone that need to replace a brass stuffing tube because it "wore out"... Just my 2 pennies...

Later,
Mike

[JIM MARCUM]

Mike, a few questions.
1. Did those stuffing tubes have a teflon liner?
2. How many nitro boats have 8 horsepower and turn 40,000 RPM?
3. Can you name a nitro or gasser engine that has the bottom end torque capible of twisting a flex shaft in half?

Why Stainless Steel VS brass stuffing tubes?
1. SS requires no teflon liner.
2. No teflon line = less resistance.
3. Even if you run your boat up on a rocky beach, it's unlikely you will dent or even bend SS.
4. SS will never get discolored or loose it's silvery shine.
5. SS can be easily shined/polished to look like chrome, and will stay that way.
6. Price wise, SS is equal to or cheaper than buying brass tubing from your hobby store.
7. SS will never corrode an aluminum strut due to dissimilar metal electrolytic corrosion. (I've had brass groumets corrode thru a 1/8" thich 2" dia aluminum tube on a full sized sailboat)
8. SS can't be beat for the COOL factor.

In the last couple of years since I got into FE boats I've had 3 brass stuffing tube failures. All were at the strut connection.

So that's the way I see it. JIM

[drwayne]

Jim, 1/4 internal.. idea on wall thickness + grade ?
W

[JIM MARCUM]

DAMN IT!!! Please see below. JIM

[JIM MARCUM]

Wayne, here's the specs on the side of the tubing:
Salem Tube Inc. 0.375" OD 0.049" (thick) AW TP 304/TP304L SMLS ASME-SA213/SA213M ASTM-A213M-09a/A269-9 NDE COLD DRAWN - MADE IN THE USA

So, thats an ID of .277". Plenty - but not too much - of clearance for .250" flex shafts. You can probably find similar stuff from a local tubing supplier. If not, I can cut some of mine to length & mail it to you for <$10 in the US. Don't know what shipping would cost me to Australia. Send me a PM if interested. JIM

[drwayne]

1.5mm wall , 304 grade
Standard 'shelf' stuff, a not so standard application here. !
Thanks for the spec
Wayne