Stuffing tubing size for 3/16" flexshaft

[Old School]

As part of an upgrade I need to change the 4 mm flexshaft on my HK Libero to a 3/16" shaft. I hope to use the Speedmaster 21 strut with rotating bushing as part of the upgrade. The Speedmaster strut requires a K&S # 131 1/4" brass stuffing tube. I am thinking that I may fit a stuffing tube with no teflon liner.

Here in lies the issue, what size stuffing tube should I use with no liner, please? I have read that 7/32" tubing is suitable. 1/4" would be convenient as I could run it right through the strut for the rotating cross drilled bushing, however, the 7/32" would make it simpler to convert the existing stuffing tube for easier installation of the stuffing tubing through the hull apperture. Would I use a combination of 7/32" tubing from the hull to the strut and then the 1/4" within the strut barrel? If a combination then how far should the 1/4" tubing overlap the 7/32" tubing?

[fweasel]

1/4" brass tube for a 3/16" (.187) cable with no liner. 7/32" brass tube is for a .150 cable with no liner.

[Old School]

Many thanks. I can see now where a mix up has occurred. I took my information from a table on the web however, it is soon obvious that the table is incorrect as the table states 7/32" for both 0.150" and 0.187" (obviously wrong).

Quote table listed on the web -

Suggested stuffing tube sizes when used "WITH NO" Teflon tubing:
5/32" brass for Octura .098 Flex Cable.
3/16" brass for Octura .130 Flex Cable.
7/32" brass for Octura .150 Flex Cable.
7/32" brass for Octura .187 Flex Cable.

As may be seen a mistake is made for the 0.187" flex as it should be 1/4" tubing (not 7/32"). Thus I would run the 1/4" brass stuffing tube from the hull opening right through the Speedmaster strut, making allowance for the aft tip of the rotating cross drilled bushing.

[rol243]

i use the 7/32 inch I.D. tube for my 3/16 inch shafts , nice fit no drag and no side slop.

[Old School]

i use the 7/32 inch I.D. tube for my 3/16 inch shafts , nice fit no drag and no side slop.

You make reference to "I.D.". Most likely this equates to a 1/4" "O.D." tube. I do see a lot of play with a 3/16" shaft in a 1/4" O.D. tube. I measured the I.D. of K&S 1/4" brass tube and it is a nominal 0.215". 7/32" I.D. equates to 0.21875". My shaft measured at a nominal 0.187".

By coincidence the stock stuffing tube has an I.D. of 0.213". Given that it is so close to the I.D. of the recommended K&S 1/4" tubing (0.215"), do I really need to remove the stock factory fitted tubing? I know that I need to run 1/4" tubing through the Speedmaster strut.

[CraigP]

No, he means 7/32” OD tube... It telescopes into a 1/4” tube. It has a much tighter fit. I use short segments of that tube to create a bearing journal at the end of the 1/4” tube, going into the strut and at the coupling, which makes alignment much better and helps to reduce water intrusion into the boat.. I would not run it as a complete length stuffing tube, seems the grease load would be compromised, but that’s just me...

[martin]

Check out the relevant sizing tables for K&S tubing & flex sizes in the OSE store under flex cable parts, these charts are correct.

[rol243]

i don,t use any grease with the shafts as i have found its not just messy it also builds up over time inside the stuffing box tube which in turn causes some drag. chainsaw bar lube oil is very good as it seems to hold on with high rpms and is not messy. not saying don,t go out and buy grease its up to the individual in selection.

[Old School]

Many thanks gentlemen, I will source some 7/32" tubing to use as short length journals either end of the stuffing tube.

[Beaux]

Just curious, why don't you want to run a liner?

[rol243]

liners can be a big let down when things get worn and warm.

[Old School]

It is not simply a matter of not wishing to use a liner or not. There are several threads on this forum and others relating to the pros and cons of liners. I have seen a few reports of stuffing tube wear relating to not using liners however, one needs to understand the history of those few occurrences. Did the operator carry out a regular maintenance procedure or not? There are numerous reports of both competition and sport operators who do not suffer damage leading to replacement of stuffing tubes. Some have run for years with the same stuffing tube without a liner.

It seems a matter of personal choice. Personally I would prefer a liner, however, others see the liner as just something more to go wrong opting for simplicity. Even with a liner installed regular maintenance is essential. I recall a recent posting on a forum where the operator reported a flexshaft breakage. When asked about his maintenance procedures his response was in several years use he had never removed and maintained the flexshaft.

As most, if not all, RTR boats are supplied with a liner then perhaps one develops a sense that a liner is essential. Reports from years ago, prior the release of 2.4ghz radio control, talk of radio interference from two metals rubbing on each other so supporting the need for a liner. However, one only needs to listen to the results obtained from competition use that not using a liner is going to cause harm to your boat. Some competition operators use liners and some do not, so really the choice is down to the individual.

As I stated previously I prefer a liner however, a recent mishap with a 4 mm flexshaft breakage lead to damage to a liner and difficulty in retrieving the liner from the stuffing tube. By coincidence I can upgrade the drive to a 3/16" flexshaft and yet still retain the same stuffing tube, minus a liner. As the boat will recieve minimal usage I can assure myself that long term wear will not be an issue as long as the shaft is regularly maintained after each outing.

The choice is up to the individual. If I was installing a new stuffing tube then for "peace of mind" I would install a liner however, that is just me being overly cautious. A liner has its pitfalls as I have experienced and can be just as detrimental to good running as its benefits. The choice is yours alone, guided by advice from others in both camps.

[MadProps]

running outboards, I learned to hate liners so I removed the liners from my stuffing tubes right away

[CraigP]

Not a fan of the liner... Never had a problem with one, but I don’t like the idea that the liner could catch on the shaft and spin in the stuffing tube. I think wear from metal-to-metal rubbing comes in from axial misalignments or too tight a bend on the stuffing tube. Also, there’s the much talked about required space between the prop dog and the end of the strut. If you’re marginal, you’ll pull the flex shaft tight and it will start to saw on the stuffing tube. But one things for sure, when it comes to a liner, there’s no absolute way to do it.

I run a sealed drive line. I have a seal at each end, stops water from breaking down the lubricants and also stops lubricant loss out the back of the strut while running. I run 15-20 times before maintenance, and the grease shows no signs of breaking down. I don’t know of anyone else doing it this way, I guess folks like to get up close and personal to the dirty flex shaft! This guy can do without that chore, I’d rather be running it.

[rol243]

yes that was the first must do performance mod for all K&B Outboards, toss the liner and fit a brass tube.

[Beaux]

Thank you.