Do i make a flat spot on my flex shaft for the drive dog?

[justski]

Hi Everyone
DO I MAKE A FLAT SPOT ON MY FLEX SHAFT FOR THE DRIVE DOG or loctite?............and do i put the drive dog tight to the strut or do i leave a gap?
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[Chilli]

The best way is to determine where to put the flat spot should go is to put the drive dog on the prop shaft with the biggest prop you think you'll be able to run and the prop nut screwed in so you have 1/4 inch of threads showing on the aft end. Slide the prop and drive dog back toward the nut and with a Sharpie, mark the shaft where the worm screw on the drive dog is located. On most of my FE's the flat spot is about 1-1/4" back from the end of the shaft.

Always leave a gap between the drive dog and strut to allow for flex compression. Conventional wisdon is the gap should be the same as the diameter as the flex cable you are using.

[justski]

cool thanks for the info ....but after i made a flat spot i tighten my prop and the drive dog still moves back i think i am going to try to take a small drill and make a cup for the set screw to sit in

[martin]

When you file the flat dont start the flat further foward than where the grub screw is otherwise when you fit the prop & nut & tighten the nut it will just push the dog foward to much . The grub screw needs to be against the foward vertical edge of the flat to stop the dog being pushed foward.

[Chilli]

I use a Dremel with grinding stone. It makes a dip in the shaft rather than a flat spot. Than I put some lock tight in the area before installing the drive dog, wiping the excess after the worm screw is tighened. After the locktite is dried I grind down the worm screw flush with the dog. Havent had a dog come loose yet.

Be careful trying to drill that small shaft. I wouldnt try it without drill press. The drill bit can easily move to one side and break. Wear eye protection and watch the fingers.

[longballlumber]

Here is some nice step by step info on setting up a new flex shaft... It starts on post #17

http://forums.offshoreelectrics.com/...n-my-Crew-Hull

Later,
Mike

[HTVboats]

The best way is to determine where to put the flat spot should go is to put the drive dog on the prop shaft with the biggest prop you think you'll be able to run and the prop nut screwed in so you have 1/4 inch of threads showing on the aft end. Slide the prop and drive dog back toward the nut and with a Sharpie, mark the shaft where the worm screw on the drive dog is located. On most of my FE's the flat spot is about 1-1/4" back from the end of the shaft.

Always leave a gap between the drive dog and strut to allow for flex compression. Conventional wisdon is the gap should be the same as the diameter as the flex cable you are using.

Just wondering how much gap you really need for wind up compression on a shorter FE shaft. My P-mono shaft is barely 3-4 inches of flex vs my gas mono with maybe 9-10 inches of flex. How much will a short shaft reall wind up? I still leave the safe diameter rule which may just put all the pressure on the motor bearing. FE motors also don't compress and fire a power stroke 1 time every revolution which could hammer and compress more. I don't know the answer here so opinions welcome. Would the rpm difference show up on a data logger or is it insugnificant?
Mic

[morewattsnow]

Somebody on this forum mounted a flex shaft in a vise and twisted it a quarter turn with some vise grips. Couldn't measure any length difference twisted vs untwisted. So how much shorter does the cable really get under load? How much does it actually twist? To much space at the strut and the motor gets the load, to little and the strut gets it. I use 1/16 to 1/8 inch and haven't worn out any strut bushings or motor bearings. Just sayin...

[martin]

I find the easiest way to mark where the flat needs to be is to put the dog where it needs to be & then tighten the grub screw, undo & remove the dog & youll see the mark that the screw has left on the shaft. Then simply file the flat.