Teflon stuffing box/shaft tube liners -- good or bad?

[1945dave]

Being of the old school, make that very old school, I have seen flex shafts and teflon lined tubing for over 40 years. I am somewhat surprised at the popularity of teflon liners still used today. What would be really interesting to me is to know how many record setting boats have set records while using these liners??? Do you use these liners or do you not?

[Jeff Wohlt]

Nope...you also have to remember the bigger the cable the more wear on a liner...to the point of it melting. We also never had the power or rpm back then as we do today. It still works but brass works well. Cap the motor end with a vac nipple and put a hole in it to stop any water coming up the tube. A cable is like a pump.

[b20btec]

Nope...you also have to remember the bigger the cable the more wear on a liner...to the point of it melting. We also never had the power or rpm back then as we do today. It still works but brass works well. Cap the motor end with a vac nipple and put a hole in it to stop any water coming up the tube. A cable is like a pump.

That's very Interesting I'm going to have to try that on a single motor setup. I get the cvac plug but the drilling a hole. If I'm following your statement, you're saying put a hole into the brass stuffing tube. This will create the low pressure for water to escape instead of running up into the motor and collet. Can this be drilled in a catamaran in the section right where the tube exit the hull? Thank you for the wonderful post and ingenuity.

[MarkF]

I still use Teflon in my saw boats and so do half of the others that come out. I don't use it in my gas size sport hydro but everything else I do. They also use it a lot over in Europe, even on all of the big cats.

Mark

[iamandrew]

well apparantly the teflon has a pretty high melting point, so to be honest if you melt your teflon liner, its probably somthing in the drive setup thats caused it

https://www.google.com.au/search?q=teflon+melting+point&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

I havent really had any trouble with teflon liners, but i do "glue" them in using spray on glue. seems to be enough to fix it in and stop it from rotating, but easy enough to remove it

[h2o 1]

That's very Interesting I'm going to have to try that on a single motor setup. I get the cvac plug but the drilling a hole. If I'm following your statement, you're saying put a hole into the brass stuffing tube. This will create the low pressure for water to escape instead of running up into the motor and collet. Can this be drilled in a catamaran in the section right where the tube exit the hull? Thank you for the wonderful post and ingenuity.

What Jeff is saying is,put a hole in the vac nipple,not the stuffing tube.

[ManuelW]

important things when using teflon liner:
-only one bend, no "S" curve
-smooth bend, not sharp edgy
-have still a round shape, not an oval one
-good alignment to the drive and the motor/coupler

These are the few rules from my experience. I also use Teflon liner in all of my boats, also the high rpm SAW boats with 1/4" flex cable and 60mm props - works excellent and almost without friction.

regards,
Manuel

[BHChieftain]

important things when using teflon liner:
-only one bend, no "S" curve
-smooth bend, not sharp edgy
-have still a round shape, not an oval one
-good alignment to the drive and the motor/coupler

These are the few rules from my experience. I also use Teflon liner in all of my boats, also the high rpm SAW boats with 1/4" flex cable and 60mm props - works excellent and almost without friction.

regards,
Manuel

Hi,
Why not an S-bend?

Chief

[b20btec]

What Jeff is saying is,put a hole in the vac nipple,not the stuffing tube.

Thanks for clearing that up, I had the drill ready to go.

[ManuelW]

@ Chief:
I'd say less friction and it runs smoother. Here in Europe in FE its absolute standard to use flex shafts without any "S"-bend. The only ones here who use an "S"-bend are guys with gas engines and turbines as its often impossible to place it without one.

regards,
Manuel

[BHChieftain]

Some say an S-bend results in less friction and whipping effect vs. a U bend. I have 2 similar boats, one with S-bend, one is straight, they both run silky smooth. I wish I had one with a U-bend so I could compare 'em...

Here's an interesting demonstration:

http://www.youtube.com/watch?v=pwq-3x0nLl8

Chief

[siberianhusky]

Some that do some that don't, I don't run a liner, been at it since the 80's and never have. I firmly believe in KISS or if a part isn't on the boat it can't fail. Since I've never had a problem with plain brass, for me I see no reason to introduce another part for a solution to a problem I've never had.
The finger dyno says both my Motley Crew and SV27 have less shaft friction with a plain brass stuffing tube vs the stock setup with teflon. No idea if it made any difference, made the changes before I ran either of the RTR boats I own.
I honestly think it comes down to what you have experience with and are comfortable running. I've only seen a few pictures of exploded stuffing tubes due to teflon failure. Pretty rare either way if the driveline is set up properly and well maintained.

[1945dave]

Interesting view point. I have been running flex shafts since the early 70's. Regarding "S" bends, testing verified that "S"bends reduce whip and vibration. Not necessarily less friction. On the other hand many guys running outrigger hydros took out a solid shaft and slipped a flex cable straight in with no curves of any kind and had good results. The next phase was to take standard outriggers and hang a strut bracket on the back and have the ability to make small adjustments with respect to prop depth and prop thrust angle. Impossible to do with a solid shaft but the main point was there was no gentile curve or "S" bend just a dead straight tube with a long 22 inch flex cable. We would remove the spacers and the 5 bearings and shove the flex shaft inside the pre-existing brass shaftstuffing box/tube. No problems great results. Oh. no teflon sleeves either.

Dave

[Brushless55]

Some that do some that don't, I don't run a liner, been at it since the 80's and never have. I firmly believe in KISS or if a part isn't on the boat it can't fail. Since I've never had a problem with plain brass, for me I see no reason to introduce another part for a solution to a problem I've never had.
The finger dyno says both my Motley Crew and SV27 have less shaft friction with a plain brass stuffing tube vs the stock setup with teflon. No idea if it made any difference, made the changes before I ran either of the RTR boats I own.
I honestly think it comes down to what you have experience with and are comfortable running. I've only seen a few pictures of exploded stuffing tubes due to teflon failure. Pretty rare either way if the driveline is set up properly and well maintained.

is there a rule of thumb for how much bigger the stuffing tube needs to be vs the size of the flex shaft?
I jacked my teflon lined stuffing tube today and took out the flex shaft with it in my PMono, now I need to rebuild it...
thanks

[1945dave]

Yes there is a rule of thumb. But it is not etched in stone. You want the diameter of the inside of the tube to be a loose sloppy fit larger than the outside diameter of the flex shaft itself. Years ago when the norm was to use very thin flex cable (some were even wire shafts not stranded cable) it was thought that you should make the shaft log or tube as tight as possible without binding the rotation of the cable under load. This theory believed the tube gave strength to the flex cable by not allowing for knotting or kinking. In truth there is some evidence that this was true. However with the quest for speed it also said if you make the fit sloppy loose then the resistance was minimal and you went faster. So if you are looking for numbers as the answer I like the 1/3rd rule. Make the ID (inside diameter) of the sahft log 1/3rd bigger that the OD of the flex shaft. Most tubing is sold by the OD size. But all tubing suppliers can give you the nominal ID diamension as well. Typical thin wall K&S hobby grade tubing has a wall thickness of around .014. So K&S tubing make sliding fit step sizes available so that the ID of one size is close to the OD of the next smaller size. For example 1/8th flex cable (.125) you would like to use 5/32 inside diameter tubing or maybe 3/16th OD. 3/16th flex cable (.187) we like 7/32 tubing or 15/64th tubing. !/4 inch we like 9/32 ID or 5/16th OD tubing.

Now just for my opinion, I do not blieve a teflon sleeve brings much to my party.

Dave