Flex Shaft Broken?

[pulliamt]

Hi...I have a Miss Bud 1/12 and have been having some flex shaft problems I was hoping to get some help on...

The boat runs great for 5 or 10 minutes and then all of the sudden it revs like the prop is cavitating. I bring it in and can spin the prop and shaft without spinning over the motor. However, I cant tell where it is slipping because the prop and shaft (as much as I can see going into the bottom of the boat) spin, but the portion of the shaft attaching to the collet doesn't spin. In other words, it is like the shaft is broken in the middle somewhere in the stuffing tube.

When I pull the shaft out it appears to be fine. No visual evidence of being broken.

Is this normal when a shaft breaks? It has happened to three new shafts now and this is getting to be a pain! I called Horizon and they keep replacing the shafts but they don't have an explanation as to what the problem is or what may be causing it.

I recently replaced the prop with a metal octura y535. Could this be one of the problems? Is the stock shaft not strong enough to support this prop? Or...Could I coincidentally be hitting something and now that the prop is metal and doesnt break, it breaks the shaft because it is the weakest link?

Any help whould be appreciated! Thanks in advance!!

[Burkey1000]

When you say when you take the shaft out it looks ok, does it have a flex shaft or a solid shaft, try and take a pic of the shaft out the boat, a picture can say a thousand words. :)

[pulliamt]

It is definitely a flex shaft. What I mean by it looking ok is that it is in one piece and the windings dont look broken or loose at the solder points.

[dhutch]

I know nothing about boats, but its a flex shaft, see title!

[blizard05]

shaft sliping in collet? drive dog sliping on shaft?

[Burkey1000]

as above, they have been known to slip on the collet and the grub screw can seem real tight. remove the gub screw from the collet clean and replace tight with threadlock and do the same with dog drive, should sort ya probs out. :)

[pulliamt]

Its not slipping in the collet or the drive dog....I can see the shaft spinning as it goes into the bottom of the boat (which to me means that it is not slipping at the drive dog), but the shaft is not spinning at the collet (indication that it is not slipping in the collet). It is just like the shaft is broken somewhere in the middle, but visually it's not. If you can imagine, it is like the wrapping is slipping on the inner shaft part. The wrapping is held tight at the collet, but the prop spins the inner shaft.

[mjmsprt40]

Now you've got my curiousity. At each end, it's the outer covering that does all the gripping. The collet grips the outer wrapping, and at the prop end, the stub shaft is usually silver-soldered or brazed onto the outer wrap. The inner core could be broken at the middle of the shaft (which means the shaft must inevitably break completely) but as long as the outer wrap maintains its integrity and as long as the engine collet grips it securely, the stub shaft must turn at engine speed. I don't think anything is welded or brazed in a direct way to the inner core.

[blizard05]

REMOVE shaft from boat,clamp motor end in vise,DO NOT over tighten. just enough to hold shaft. using gloves or a rag,try to turn prop. (what happened?) did prop turn? did prop and shaft turn?

[Burkey1000]

The shaft is not broke, its not slipping in the dog drive, its not slipping in the collet, but its not working. Doesnt make sense, take the whole thing apart and check, if its not broke and not slipping anywhere its gotta turn. :rolleyes:
not spinning at the collet (indication that it is not slipping in the collet). JustDoesnt make sense what ya saying. :confused: Is the prop tight and not just spinning on the shaft.

[mjmsprt40]

Maybe he has a phantom prop shaft???

I wonder if it's possible the collet IS slipping at full power, but maybe not so much that you would notice with the boat on the stand and the engine off.

Otherwise, what we're being told here is outright impossible. We're told that the propeller and stub shaft turn by hand, showing the drive dog is secure (want to bet???). The cable is NOT turning at the engine collet while turning the propeller. However, when you remove the cable from the housing, there is no break. Naahhh, something else is going on here, and we're not being told what it is yet.

[blizard05]

Yes, some info is missing here.

[pulliamt]

Im not sure what other info to give here....It seems very strange to me too. I will try and mark up a picture oand post it to explain what I mean. If you can imagine, it is like the solid piece that the windings wrap around is slipping inside the windings.

Hopefully this will help explain it...I just got two more shafts from Horizon, so hopefully I can run it this weekend....

One thing though, back to my original question....Could the stock shaft be too weak for the metal prop? Should I go back to the plastic stock prop to insure more "play" time?

Thanks for everyone's help!

[blizard05]

OK,you have a 2 pc drive shaft.Flexcable,ferrule, and stub shaft.Does ferrule come soloderd to flex shaft?does stub shaft spin in ferrule,does ferrul spin on shaft?

[mjmsprt40]

Something seems mighty familiar about that setup. I look at that ferrule and I see a setscrew. Now, I can't be absolutely certain because I'm not the one running this shaft, but I'm reasonably sure the setscrew may be backing out at least slightly while running. Add a metal propeller--- you DID remember to balance that prop, didn't you???--- and you can have just such problems as you have mentioned. The setscrew backs out slightly, the stub shaft spins in the ferrule, and no amount of engine power will turn the prop once that happens.

Way back in the bad old days before we had to muffle our engines, I had a SK-Daddle 40. It ran a solid shaft, so breakage of the shaft couldn't be a factor. I would do good to get ten minutes of running before I would at least loosen, and usually throw, a setscrew somewhere in the drive. Back then, I didn't know diddly about balancing propellers so I ran them as they came out of the package. The result was that not even Red Threadlock could hold a screw for long, and--- the engine would scream and the boat would go nowhere fast.

Balance and sharpen your props. Use threadlocking compound on every setscrew in the drive. It can't hurt, probably will help.

[blizard05]

What about the rest of shaft,4 more pcs ,Stub shaft,drive dog ,prop,and prop nut? PICS?

[Burkey1000]

Ok if you think its slipping from the inner core, get your flex shaft, and silver solder the end of the flex shaft that goes into the engine collet.Make sure you solder all the end of it then smooth out the solder with a dremel etc to fit back snugly inside the collet, then if you want re solder the ferrel. You should always siver solder the felx at the collet end to stop the flex unwinding, do this then there is no way it can slip at all. Should solve the problem, if it doesnt then its gotta be your grubsrews. Is you collet insert the correct way around, get it tight but dont overtighten, you will know if its slipping in the collet because it will be worn and shiny. :)

[blizard05]

IS IT FIXED YET ???? what was wrong??

[Burkey1000]

we are waiting to see if its sorted yet no reply, hmmmm. :)