Flex shaft problems

[dwilfong]

I am having problems with the 1/4" flex shafts in the new boat I am running.

Never had a problem till this set up.

The tube and shaft go strait to the strut no bends at all. It is a strait shot.

I have balled up two shafts right where thy go in to the tube.

Has riped the tube right off the end and shredded the cable. the last cable broke at full song and spit what was left of the shaft out the back.

This last time was right after greasing the cable. Check the line up of the cable and tube after every run.

There is less than a 1" between the tube and the eng.

Have tried two different lubes lubraplate 105 and good red stringy grease. Both do the same.

This has me really perplexed.

Should also state I have broken 2 props in testing also.

The mono is over 15lbs. and running a big prop hard at high RPM.

Never had this problem be for need some input.

David.

 

[Philmunsterman]

David, I'm curious. Do you Silver Solder the end of the Shaft that fits into the Coupler ? Phil

 

[dwilfong]

No have never don that to my shafts.

 

[Tim Kish]

Inch space seems like alot to me David , may not be the problem but I keep that as short as possible.

Tim

 

[Steven Bryant]

Have you got any pictures of the setup

 

[bermudadude]

stiffen the motor mount bushings.when the motor torques (im gonna guess its a big block power plant) the motor twisting throws the flex out of alignment and since theres ALMOST no bend (i imagine theres somethin) its alotta flex to wobble. also like previously stated make sure its less than 1/2 inch showing outside the tube,make it barely enough space to take the tightening end of the collet off.also if ur not using a T-bar type setup use wood to support the tube real close to the end ,like 1/4"

 

[dwilfong]

Already got it gutted out of the boat.

Not much to look at just a T bar and a tube going strait back to the strut NO bends at all.

Set it up with a 1/4" steel rod to line it all up.

The only thing I can come up with is with a strait shot there is no bend in the tube to let the flex cable arch in the tube?

The cable might be to neutral and whipping around uncontrolled?

 

[Tom Foley]

Engine is moving around too much and dead straight is no good .

 

[Buckshot]

Engine is moving around too much and dead straight is no good .

Like trying to push a rope.

 

[dwilfong]

Ya thats my thought pushing a rope.

No bend it dose what it wants.

Now to fix it?

The eng is down in the bottom and it loves it there. Dose things a gasser will never do.

The CG is real low.

Have to raise the strut to run on the tips of the big props to get the speed.

Now what GO SLOWER with small props or F up the CG?

Is there not a T bar with a bearing in it for the shaft? Who makes one?

Or a square drive strut setup.

 

[dwilfong]

So put a belly in the tube to stabilize the cable this will take the whip out?

 

[Tom Foley]

Yep otherwise the shaft become a " jumprope "

 

[David Santistevan]

I have seen similar problems caused by harmonic vibration. This would be a function of the length of the shaft and the rpms of the engine. Under certain circumstances if the shaft is just the right length to resignate with the vibration of the motor it will begin to whip (actually I think it's trying to create a sine wave). The bend might help to solve that because you would be changing the free floating length of the shaft. You could also try a piece of silcon tubing on the shaft between the stiuffing tube and the collet. This would act as a vibration damper.

Just a thought.

D

 

[stan simpson iv]

Dave you got a pm...

 

[moparbarn]

if it's dead nuts straight, why not run a hard shaft?

 

[dwilfong]

Thought about it but trying to make it simple. This boat is for a buddy.

Need to make it easy for him to run and maintain.

 

[dwilfong]

Thanks Stan!!!!!

GOT IT

 

[stan simpson iv]

David,will send you a pic of one I made.

 

[dwilfong]

Great would like to see the pattern.

 

[barry petrowski]

May want to try a thrush washer set up at the strut, may keep from the pushing rope effect