Brass or Teflon liner?

[jaxracer]

Brass, teflon or other, has anyone done A/B testing to see which lower unit liner insert creates the least amount of drag on the flex cable? I figure the electric guys might have some good feedback as they can look at the battery draw between the options. Not concerned with durability here.

Thanks!

 

[K F Wheeler]

Good point!
ken

 

[topfuel443]

I can tell you with 100% certainty the K&B made cables in a 7.5 are far easier to turn than a lawless strong arm cable, from an amperage draw setup, everything else being the same. They are MUCH more flexible.

 

[topfuel443]

I personally run brass.

 

[David Ashcroft]

...

 

[SayMikey]

Brass for me

 

[Kris Flynn]

I wonder if the brass is mainly better for the extra support it provides...teflon has a far better friction co-efficiency, but I know shafts last longer in brass tubes in some lower units (k&b for example). Lawless and OS units have good shaft life with teflon...

 

[jaxracer]

I wonder if the brass is mainly better for the extra support it provides...teflon has a far better friction co-efficiency, but I know shafts last longer in brass tubes in some lower units (k&b for example). Lawless and OS units have good shaft life with teflon...

See that’s what I was thinking Kris. Teflon has a much lower co-efficient of friction than brass but based on width of tube, etc, I was wondering how much of a difference it actually made in real world data. Interesting note there Gabe, never thought of the difference just between the different brands of flex cables. I wonder where OS ranks in there as I’m pretty sure they have a relatively soft cable too.

Still think we have to figure out how to create a wire drive or a friction-free solid shaft setup for outboard use. Based on the leaps and bounds they have made in hydros, I wonder how far it would allow us to push tunnels to go.

 

[HTV Boats]

The downside of teflon is when a shaft breaks it balls up and can ruin a drivetrain. Outboards lowers generally are split halves so an easy fix vs an inboard shaft. In my mind once a flex shaft is spinning soft or hard makes little difference.
To me the real power robber is the prop shaft that wears out of round. The OS far superior to the K&B or Hyperformance which the bearings wear too fast. I know John Albritton made some good prop shafts with better materials but not cost effective to mass produce. I believe Gabe has also worked on some. Getting proper clearance is critical.

 

[DougSick]

I run my flex so that it goes into a bit of tension when running. This keeps the cable from twisting up. The teflon liner definitely helps keep the friction down in this case. Jim Wilson convinced me on the merits of keeping the gap small between the strut and the drive dog thus allowing the flex to pull a bit of tension into the cable so that it doe not flop around and bind in the drive tube. I run a delrin washer ahead of the drive dog to reduce friction when it pushes against the strut.

 

[Tom Foley]

I run my flex so that it goes into a bit of tension when running. This keeps the cable from twisting up. The teflon liner definitely helps keep the friction down in this case. Jim Wilson convinced me on the merits of keeping the gap small between the strut and the drive dog thus allowing the flex to pull a bit of tension into the cable so that it doe not flop around and bind in the drive tube. I run a delrin washer ahead of the drive dog to reduce friction when it pushes against the strut.

So with the engine moving back and forth on the mount under load you try to limit the shafts movement by pushing against the strut thereby effectively stretching the shaft , causing it to pull on its grip in the collet ?

 

[Daniel's Racing]

I run my flex so that it goes into a bit of tension when running. This keeps the cable from twisting up. The teflon liner definitely helps keep the friction down in this case. Jim Wilson convinced me on the merits of keeping the gap small between the strut and the drive dog thus allowing the flex to pull a bit of tension into the cable so that it doe not flop around and bind in the drive tube. I run a delrin washer ahead of the drive dog to reduce friction when it pushes against the strut.

What kind of a engine/collet/cable/stubshaft setup are you using the tensioned up cable setup on/with ?

Most or us run welded stub cables. You don't want the drive dog getting anywhere near the strut with those. Any tension at all on a welded stub cable and it will fail in short order. Never mind the joint but the entire cable is going to heat up the brass stuffing tube(or melt a teflon) if forced to run hard against it.

Most other drive setups are square at one end so no way to set up tension in the cable.

Never heard of this tensioning the cable idea before but seen what happens when a round collet setup has the cable too short. Tears everything up if it doesn't yank it out of the collet completely. Plenty of expirience with this and it is a very bad thing for so many reasons.

The cable does not need to be in tension to keep from doing anything.

We run these free floating cables on 61CC 15 horsepower at 20,000 rpm. The drivelines often outlast the boats when done correctly. That includes water cooling the stuffing tube but serious power running close to 80 mph pushing big heavy Superboats.

My Speedfreek Apache boat build and cable setup won this years Superboat shootout again this year with Jorge Ruiz owner/driver with Orange Madness Team. We won it in 2020 too.

Square drives are a floating cable. Round collet welded stub are a free floating setup with drive dog never touching when pushing forward. Only pushing on cable into the engine.

Boats handle different when the thrust is pushing on the engines collet versus at the strut( arguably they do, lol ??). I do not think you would want it to be transitioning from one way to the other constantly.

 

[DougSick]

I am running brazed cables I build myself. For a .21 hydro, I leave about 1/16 gap and on larger boats, about 3/32. Never had a problem with the cable pulling apart. The cable goes into a bit of tension but not much. The rubber mounted engine engine will move a bit if it gets into too much tension but I think that's better than a 1/4 gap pushing totally on the motor and causing the cable to spiral inside the drive tube. All that pushing on the cable and it has to go somewhere and that's in a spiral. If you look at a cable that's run inside of brass, notice how it's shiny in some spots and not in others. That's the cable going into a spiral inside the tube. If it was shiny all the way or at least in the bend portion, then it's not spiraling and chewing up energy. If the drive tube has to be water cooled, then I'd say there's a lot of spiral going on and a lot of internal friction. I do see some wires breaking occasionally but I suspect that's due to the heat applied to the braze area and taking the temper out of the cable. Easy fix to install a new cable in my shop. I'm speaking from my experience and not saying that anybody is doing it wrong. I just do another way and I just happen to agree with a guy that had some very fast boats. If you feel that large gaps work for you, I can't tell you different and I'm just happy with the way I do it.
I've been around the whole evolution of drives from straight shafts to U Joints to square drives and now brazed cables.
I saw a u joint set up once that totally fascinated me as the prop was turning in the breeze while the engine was out. Virtually frictionless. Can't say that a cable would do the same.

 

[DougSick]

So with the engine moving back and forth on the mount under load you try to limit the shafts movement by pushing against the strut thereby effectively stretching the shaft , causing it to pull on its grip in the collet ?

Yes. But it's a fine balance. Too little gap and the tension can be too much. Just want it to lightly push on the strut. I can tell how much push I get by how the delrin washer wears. No wear, and I'm pushing all the time on the motor, a little bit of an indent from the strut and that's about right. Heavy grooving/distortion means too much tension. I don't want too much tension either but the rubber mounts easily take up the movement and I've never had a cable come out of the collet.

 

[Tom Foley]

Glad it works for you but from my experience these engines and shafts move around up to 3/8" . I let them do what they want to do or they will move the strut with .91 engines .

 

[Grimracer]

I am with Tom!

to qualify.. 1/4 gap pushing on a LARGE roller bearing.. I like that.. I will take that!

Cable spiral also eliminates cable whip! You want to load the cable in more then once place along its length.. thats why S bends work just fine!

Grim