View Full Version : Graupner Flex Coupler Overheating - ideas needed
07-25-2003, 08:12 PM
I've been using a 5mm to 4mm Graupner flex coupler on my Super Hawaii, and while in theory this should be a relatively maintenance-free system, mine has proved fairly disastrous.
I started out and the first coupler I bought was not drilled straight, so it created a lot of vibration and I couldn't keep the set screws in even with Loctite.
My second coupler worked fine for about ten runs, and then the shaft somehow unbonded itself from inside the coupler itself. I tried various remedies, including:
1. I used 30 minute waterproof epoxy to glue the shaft into the coupler. This worked for all of a minute on the water before it came apart.
2. I used solder and soldered it in place, (the solder being inside the coupler cavity, not gobbed onto the end. This worked for maybe two minutes before it started slipping.
I gave up on that coupler and went ahead and ordered another one, hoping that maybe the second one coming apart was simply a flaw from the factory and it wouldn't happen again. First outing tonight with the new one, it comes unbonded after three minutes.
I have a theory regarding what is happening. I noticed (for the first time tonight) that the entire flex shaft, and couplers, are quite warm (hot?) after just the three minutes. The solder on the second coupler seemed to work okay, and I couldn't break the bond by twisting by hand before I installed it in the boat, which tells me that the solder bonded suitably for my application. My theory is that the flex shaft becomes warm enough to melt the solder after a few minutes of driving. Perhaps this is the same thing that happens to the epoxy as well, with a similar heat related issue.
I keep the shaft oily and greasy and there is probably a 20 degree bend over the length of the coupler, so I don't think there's too much.
What am I doing wrong, and what's a good fix? Is there some bonding agent that will be strong enough (given that there is really almost no surface area inside the coupler to bond with) and that will be able to take the heat? I can't afford to be buying couplers for every 3 minutes of run/
07-25-2003, 08:26 PM
The problem is that the only thing holding the flex in the hole is glue. To remove the glue we use heat, so your theory is problably correct. But on our flex shafts we also use set screws.
07-25-2003, 08:52 PM
Do you mean the set screws that attach the coupler to the output shaft and motor shaft, or are there other set screws on yours that hold the shaft to the coupler?
Do you think that I could tap my own holes into the shafts I have and put my own set screws in? My father suggested doing this but I was leery because I didn't know what would happen to the wires that comprise the flex shaft if they had a set screw jabbing into them.
If yours have the second set of set screws, I may be placing an order. But I'd really like to find a way to salvage these couplers...
07-25-2003, 09:05 PM
If you have the ability tap two holes on each end that go into the flex. That should solve the problems.
07-25-2003, 10:11 PM
[QUOTE]Do you mean the set screws that attach the coupler to the output shaft and motor shaft, or are there other set screws on yours that hold the shaft to the coupler?[QUOTE]
What Steve was saying is that where the flex cable goes in, it is glued and also retained by separate grub screws, these are in addition to the grub screws that tighten against the drive shaft and the motor shaft
[QUOTE]Do you think that I could tap my own holes into the shafts I have and put my own set screws in? [QUOTE]
Curtis this would be fine, heat up the end that is still glued, and just cross drill and tap for 2 extra grub screws per end.
[QUOTE]My father suggested doing this but I was leery because I didn't know what would happen to the wires that comprise the flex shaft if they had a set screw jabbing into them.[QUOTE]
It may be an idea to clean all the glue off and solder the ends a little to toughen them up, just like you would the end of a flex shaft.
[QUOTE]If yours have the second set of set screws, I may be placing an order. But I'd really like to find a way to salvage these couplers... [QUOTE]
Steve's connectors are beauties but I am sure yours can be saved. Curtiss but I think we are missing a key point here, I don't think it is normal for these connectors to get that hot??? are you sure they aren't rubbing up against something?? I use the same connector in my Taifun and I have had no problems at all for over a year... just curious... hope it helps
07-25-2003, 11:40 PM
I thought it was odd that they are as hot as they are too!!!
Nothing is rubbing, theres not really any binding in the system. Thinking about it right now though, there's something I remember. Ever since I first installed the whole system (per Jeff Wohlt) I noticed that the springiness of the flex coupler sorta pulls up on the end of the output shaft. When we were bench testing we noticed that the output shaft was getting really hot, but because it is in the water, it stays cool. Could the fact that the flex coupler not have any water on it be making it hot?
What can I do to remedy this and get temperatures down?!!
07-26-2003, 07:45 AM
Over the last year I have seen seen six of the Graupner couplers let go. they were all on Taifun Hydro's when they spun. Some were almost new and some had some runs on them. I have seen two of them made so crooked that they were unuseable. In all these cases heat was not a factor at all. The Taifuns do not put hardly any bend on them at all and still they went. In no case did the flex part break. Always the glue joint. A close look at the ones that let go shows almost no glue at all in the hole and on the flex ends. They don't use enough and what they do use isn't good eneough. I have rebuilt one using a bit of Octura flex and Loctite sleeve retainer. I haven't yet tested it .I have more on the bench to rebuild . Whatever happens they will be better than they were from the factory. I will let you guys know how they turn out.
The one's Steve has for sale are as good as it gets. Glued and screwed on the flex and using .150 dia flex too. Very strong. They have been holding up well in the Cen Auqua Jets and that puts a big curve on the flex too. n.h.schmidt
07-26-2003, 08:57 AM
Ned I have looked at Steve's connectors and as I said they look scweet, almost as nice as yours..;) LOL, anyway they are definately bullet proof looking, but any idea why the connector heats up?? is it just the torque placed on it?? I have a few of the graupners and haven't suffered any problems but I will say these are all older production, just curious, the nice thing about the connectors you are producing is that you could get a custom size! very nice! cheers eddie
07-26-2003, 09:13 AM
The problem is they are designed for low speeds and not meant for high speed and when the go for high speeds, it changes their alignment and should change the whole system to comply with the situation of the higher rpms! Ned's couplers are a CLASS ACT cause i have some and are very good!! Also Octuras couplers of which are hex-flex are good too! The universal joints are a lot of the problems boaters endure and waste a LOT of power!
07-26-2003, 09:17 AM
Mr. Curtis Chase; do have a GOOD picture u could share of the coupler area and the whole drive system from motor on thru prop?? Thanks!
07-26-2003, 09:28 AM
We have used Neds Connector up to 16cells, SS1 & 445 with no problems so far.
07-26-2003, 11:20 AM
Originally posted by n.h.schmidt
H In no case did the flex part break. Always the glue joint.
I had one break both ways. Sent the first one in for replacement, i got one back and it was crimped onto the shaft. After a few runs the shaft itself broke, but that happened when I was abusing it over 1 1/2 ft waves. I think my motor was moving a tad and it finally moved to much.
07-26-2003, 03:38 PM
Note I only bought one ... just before I found it was completely unusable due to its roll-out ... I'll never force a good motor to run this nightmare !
(Graupner quality deeply varies upon their products ... And this seems to be one of the worse possible ...)
07-26-2003, 09:32 PM
Well if I get the time I'll try to tap the couplers. I think I'll just get one from you Steve though.
07-28-2003, 10:37 AM
Hey Curtis, Sorry to hear you are having problems with your Graupner Flex. Mine still has not broken. I know this does not help your problem...basically those connectors are junk from the start. I would go ahead and yank the ends out and drill set screws...drill all the eway through so you have 2 on each stub end.
One thing I do is put the brass bushing in front of the connector at the drive...use an existing one after putting bearings in all of it...which I think you have done. The shaft has no play in mine at all.
This was a quick way to put a 700 in the hull without any mods as far as CG, etc.
Even though mine has not broken, I am replacing it with all new hardware and flex cable...or wire drive... but getting rid of the strudder and factory hardware which mkaes it handle poorly anyway.
07-28-2003, 10:46 AM
Thanks for the reply Jeff.
You make it sound like I don't like your system. I think it's probably the most simple and effective method of any of those I have seen. I love it, I just wish those flex couplers weren't total junk.
I'll add in the bushing. If I had the time to get everything set I would be getting a different outdrive and completely re-doing the set up, but I'm leaving for vacation in two weeks and after I mail ordered everything I wouldn't have any time to get the boat set up.
07-28-2003, 03:02 PM
Curtis, I have some stock ordered for strut brackets, etc. Maybe we can build them at the same time.
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