Help Please Flex shaft replacement.

[boatmanpete]

So sorry, I have thought of one more question. I have decided to use epoxy and I have jumped to the conclusion that you dip the end into the epoxy, wipe off the obvious excess and then leave it to cure before fitting. (rotating it slowly to retain an even cover. Then, I have guessed when it is rock solid you sand (wet and dry) off any spots which prevent an intimeate fit.

BUT BUT BUT Maybe you meant the fit to be done while the epoxy is still tacky.

Please advise. I am most grateful for all the advice you have provided thus far.

Best wishes

Peter

[Bug777]

Once you get it repaired & in the boat install a collet onto the flex shaft between the motor & stuffing tube. This will stop the shaft from falling out in the future. I learnt this after losing 2 flexshafts with alloy props in 4m of water.

[JIM MARCUM]

If going the epoxy route, I'd clean up the last 4" or so of the flex drive, collet end, with acetone & hang it collet end up till it's dry. Mix a small cup of good quality epoxy and, wearing gloves, work it into and rotate the last 3/4" of the shaft. Afer 24 hours the epoxy should be cured enough to remove any excess epoxy with a sanding block. Grease the drive up. Done. JIM

[JIM MARCUM]

Not so, yes you have the smaller inner core going down into the stub hole but you also have the outer wind brazed to the inner core + the braze extends along the outer wind of the flex at the butt of the stub & flex for around 1/4" - 5/16". These flexes hold up fine to gas motors turning 70mm 3 bladed props. Just about every 1/4" flex & stub is made this way.

Martin, I have twisted one out of the prop shaft last year running a Leopard 5692 1090kv motor & 68mm prop. It may have been my fault for not leaving enough room for shaft shrinkage.

That said, I'll stick to a 100% 1/4" flex drive & machined prop shaft. JIM

[martin]

Jim as with any flex they do break from time to time & all of the 1/4" gas flexes ive seen break has been at the front of the brazed joint, this is 1/4" - 5/16" in front of the butt between the outer wind & the stub. where they have broken their was no step down in the flex but full diameter that had broken, obviously a shear point going from a flex to a ridged part of the flex but it wasnt the step down that caused the break on the flex.

[JIM MARCUM]

Jim as with any flex they do break from time to time & all of the 1/4" gas flexes ive seen break has been at the front of the brazed joint, this is 1/4" - 5/16" in front of the butt between the outer wind & the stub. where they have broken their was no step down in the flex but full diameter that had broken, obviously a shear point going from a flex to a ridged part of the flex but it wasnt the step down that caused the break on the flex.

IMO, the brazing process weakens & de-tempers both the full 1/4" flex shaft & the cut down section. I've seen 1/4" brazed cut-down shafts fail on gassers too. I suppose you could re-temper a cut-down flex drive by heating the prop shaft/flex with a toarch & quenching in motor oil. But, there's no getting around the fact that a 1/4" flex shaft cut down to 3/16" is only as strong as the remaining 3/16" section. In fact it's weaker than standard 3/16" shaft.

Why? To build a step down flex shaft, the outer - first layer - of counter clockwise wire strands are removed, the second layer of clockwise strands is the new "outer" layer. After brazing the cut down flex into the prop shaft, the the torque generated in turning a 65-70mm LH prop will un-ravel/twist the outer flex strands and weaken the remaining inner strands. The pictures below are of my sheared FE 1/4" step down drive. NOTE: it failed in the 3/16" cut down section, and the Braized 1/4" section remains in tact.

On the other hand, I've never seen a full 1/4" diameter flex drive break/shear at the prop shaft connection, have you? JIM

[martin]

Jim i agree with you re full diam flex going into the stub being a much better way, but unless someone can have a custom shaft made in the way you discribe then their stuck with the way nearly all these flexes are made. Martin.

[Jeff Wohlt]

Nah...I braze them at 1100 degrees and so does Ed Hughey. No problems I know of. You also let them cool by air...no quenching them in cold water.

[Jeff Wohlt]

Some of mine have broken early on when beginning but learned they must be tinned all the way thru first then assembled. This puts the load on all wire. Not easy and Ed still makes one of the best I know of. Brazing these things really suck....I won't even do 1/4". Ed can do those! I use 55% silver...not cheap.

[JIM MARCUM]

Jeff, to braze or not to braze, and I still don't get it. But you showed me where I went wrong when I tried brazing - DON'T quench it! I did & it failed.

When I do solder, I use 60/40 (silver/lead rosin core silver solder. But it dosen't stick (NADA!) to my SS prop shafts. If you have a way to do that, I'd love to know how.

I know you guys know how to build great drives, you're pros.

Your cut down 1/4" drives are easier to remove, don't require a specially machined SS prop shaft, have slightly less drag, and are readily available. But, when it comes to absolute strength, my full 1/4" diameter drives will beat a cut down 1/4" drive every time. JIM

[Jeff Wohlt]

You need to use flux anyway.

[martin]

Flexes are made from spring steel wire & you deff dont quench, it makes the steel brittle & will snap like a carrot.

[tryinotocrash]

Hello , not sure if you got this all worked out but they sell replacements that fit right in with no mods. http://www.rchobbyexplosion.com/Elec...arts_s/585.htm that is just one place others on E-Bay.

[martin]

These are stock Venom flexes that arnt very good Quality, thats why most upgrade to better after market flexes with any rtr boats.

[tryinotocrash]

Yes I understand this however the OP seemed to have issues with modification of the aftermarket shafts so I thought maybe he would be better off with some that fit without mods.