1/4 flex cable / stuffing tube issue

[TREVOR JENSEN]

Hi,
Just finished and ran for first time on weekend my U-3 1/8th scale hydroplane and after inspection of 1/4 inch flex cable, there is a burn mark about 2-3 inches on cable at coupler end. This mark lines up with support brace in hull which you can see the epoxy has got hot and started running. The boat requires a "s" bend stuffing tube due to not being able to fit the cowling on with the dummy engine in the right place. The stuffing tube is 11/32 OD with a teflon liner. The teflon line about 2 inches from couple end is softer then the rest as well due to heat.

The question is would i get away with running a 1/4 cable in 11/32 tubing without a liner, i know 5/16th is the correct size but the last thing i want to do is remove and make a new 5/16th stuffing tube for it. Below are 3 pics showing the stuffing tube and the brace near the coupling.
Hope you can assist me in what to do.
Trev

 

[Don Ferrette]

Get rid of that teflon liner and add an oiler, oil up every run. You may find it a bit difficult to get that teflon out if it got hot enough to discolor the brass but it's gotta go. Cut the 11/32" right after it leaves the hull and use the remaining piece as a sleeve to push the 5/16" brass thru. Go easy with some lube on the 5/16" brass and it will pass thru. I always use 11/32" sleeve when passing thru the hull, it makes tube replacement easier without damaging the hull itself.

 

[RaceMechaniX]

The "S" bend stuffing tube is a legacy FE design that unfortunately should have been moth balled years ago. It worked fine with .150 cable and low power levels, but it will add significant drag in a modern FE setup especially a 1/4" cable. It is on the order of several hundred watts of loss.

I know you probably don't want to hear this, but I would redo your driveline and motor mount so you have a single gentle bend with the motor at an angle. As Don mentioned, ditch the Teflon and run the cable in 5/16" brass tubing.

 

[ricwally]

 

[TREVOR JENSEN]

Get rid of that teflon liner and add an oiler, oil up every run. You may find it a bit difficult to get that teflon out if it got hot enough to discolor the brass but it's gotta go. Cut the 11/32" right after it leaves the hull and use the remaining piece as a sleeve to push the 5/16" brass thru. Go easy with some lube on the 5/16" brass and it will pass thru. I always use 11/32" sleeve when passing thru the hull, it makes tube replacement easier without damaging the hull itself.

Don,
I understand what you mean and are saying but do you think 1/4 flex in the existing 11/32 stuffing tube (the stuffing tube is not discolored, it is fine, and i have removed the teflon liner successfully) will work and save me a lot of work.

 

[TREVOR JENSEN]

The "S" bend stuffing tube is a legacy FE design that unfortunately should have been moth balled years ago. It worked fine with .150 cable and low power levels, but it will add significant drag in a modern FE setup especially a 1/4" cable. It is on the order of several hundred watts of loss.

I know you probably don't want to hear this, but I would redo your driveline and motor mount so you have a single gentle bend with the motor at an angle. As Don mentioned, ditch the Teflon and run the cable in 5/16" brass tubing.

Tyler,
Unfortunately the motor can;t be tilted up even a bit ( i already have had to file flats on the water cooler) for the cowling to fit.
Is 11/32 stuffing tube to big for 1/4 Flex Cable without a liner?

 

[RaceMechaniX]

Then best to remove the teflon liner and press in a 5/16" brass tube in its place. 11/32" is too sloppy for 1/4" cable.
Hopefully you have a very soft 1/4" cable.

 

[Don Ferrette]

Don,
I understand what you mean and are saying but do you think 1/4 flex in the existing 11/32 stuffing tube (the stuffing tube is not discolored, it is fine, and i have removed the teflon liner successfully) will work and save me a lot of work.

No you'll need the 5/16", there will be way too much cable whip running a 1/4" shaft in an 11/32" tube. Cut the 11/32" tube right after it leaves the bottom and about 1/8" past the tube support at the motor. The 5/16" will go thru the 11/32" tube will some lubrication. Here's an example from one of my twin builds.....

 

[TREVOR JENSEN]

Thanks Don and Tyler for your replies, Appreciate it greatly.
Looks like a 5/16th stuffing tube is going in.

 

[Kristy Wallace]

Trevor everyone has there own opinions but myself and others has run 11/32" brass logs in our 67,90 and gas hulls with no problems at all and have less friction .just sleeve the beginning 1.5" - 2" of the brass log with next size down brass at colllet end and at strut end.
Your choice.

 

[Mike Hughes]

Belly pan that motor. Then you can lower the shaft centerline. This will help with getting rid of some of the S bend.
Mike