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Flex shaft spacing problems...

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Old 08-20-2009, 10:38 AM
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Default Flex shaft spacing problems...

I've got a Dumas deep vee 40 with an OS 46 in it and I'm concerned with the spacing of the flex shaft near the engine u-joint. How much space should there be between the u-joint and the brass tube? I'm concerned that there is too much space which is what caused my last flex shaft to kink. As well, is 3/16ths a good gap between the drive dog and the strut? Thanks
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Old 08-20-2009, 10:46 AM
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Default RE: Flex shaft spacing problems...

between the drive dog and strut spacing should be the thickness of your flex cable, so if your cable is 3/16, than yes, 3/16 is good (no less).

as for the U-joint, I don't know, maybe a pic of the problem could help.

Dan.
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Old 08-20-2009, 03:05 PM
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Default RE: Flex shaft spacing problems...

if the last one kinked, i would say it's too much.
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Old 08-20-2009, 05:15 PM
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Default RE: Flex shaft spacing problems...

You should'nt be using a 'U' joint with a flex cable. There is no support for the shaft at the engine. You should use a cable collet at the engine. The gap is then created at the strut and as stated by Dan, should be equal to the shaft diameter.
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Old 08-20-2009, 05:27 PM
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Default RE: Flex shaft spacing problems...

Cool, that's what I thought. Now the gap between the u-joint and the brass tube is about half an inch. I was thinking, I should get a longer nylon tube that goes the length of the shaft so there is no gap between the u-joint and brass tube. I'm not too sure how secure the nylon tube will be, it's just something to keep it all in line. As well, can I un-solder the kinked shaft from the ferrule and re-solder a new cale to it? If so, how is this done, and what's the best solder to use. I figure it's like plumbing soldering. Thanks all
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Old 08-20-2009, 06:12 PM
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Default RE: Flex shaft spacing problems...

Silver solder.

Dan.
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Old 08-20-2009, 08:19 PM
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Default RE: Flex shaft spacing problems...

the higher the silver content the stronger the joint.
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Old 08-20-2009, 09:20 PM
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Default RE: Flex shaft spacing problems...

Repeat! Get rid of the U joint and put a cable collet on the engine. U joints are intended for solid shafts not flex shafts.
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Old 08-20-2009, 09:41 PM
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Default RE: Flex shaft spacing problems...

I modded my whole boat deepv 60 it had a submerged dive. But I just changed it over to surface drive handles much better. Also moved the engine as low as possible so the boat wasn't top heavy..and it barely has a bend in the stuffing box.
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Old 08-20-2009, 09:53 PM
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Default RE: Flex shaft spacing problems...

Great thanks! I think I'm gonna try and unsolder it. The shaft is no use to me anymore so I might as well. Whoever built it decided to switch out the recommended hardware (solid shaft with a sumberged u-joint) with a flex shaft and u-joint at the engine. I'm not sure if the guy used a u-joint because the flex shaft doesn't line directly up with the engine but I'll check. If it does I'll change it out. The only thing I'm wondering is if the flex shaft lines up with the engine and the u-joint spins straight, why would this cause a problem? I understand the first one probably went because I ran it with an unbalanced prop and flipped it and over rev-ed it. Would having the nylon tube butt up with the u-joint provide any more stability?
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Old 08-20-2009, 11:12 PM
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Default RE: Flex shaft spacing problems...


Quote:
ORIGINAL: Square Nozzle

Repeat! Get rid of the U joint and put a cable collet on the engine. U joints are intended for solid shafts not flex shafts.
OK, what he said twice. The OS .46 is threaded for 1/4"-28TPI. It's a common flex collet size available from Octura and Aeromarine. This will be tied to a 3/15" flex cable.
If you have to, redo everything to make it work as it will be worth the time and money.
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Old 08-26-2009, 05:07 PM
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Default RE: Flex shaft spacing problems...

well I have taken your advice and I'm replacing the u-joint with a collet and I've unsoldered the ferrule. I have one last question.. I think I can figure the rest out by myself. Seeing that the prop shaft and flex shaft are one peice, do I cut the old flex shaft as close to the prop shaft as possible and then resolder? Thanks
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Old 08-26-2009, 05:40 PM
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Default RE: Flex shaft spacing problems...

Typically when you buy a new flex shaft it comes with the prop shaft already installed. You cannot cut the old flex shaft from the prop shaft and butt solder a replacement back on. It will not be strong enough to take the prop torque. Just buy the correct diameter flex shaft, cut it to length so you have 1 cable diameter gap between the front side of the prop drive dog and the strut and full engagement into the cable collet on the engine. It is recommended that you fill the engine end of the cable with silver bearing solder like Sta Brite before you cut it to final length so it doesn't crush when you tighten the collet. Wash the cable end in acetone or MEK to get the oil out, Flux the cable end real well and then melt in the silver solder so it fills the gaps between the strands of the cable. Don't just lay the solder on the surface. It has to soak in. You can remove the excess with a file or a hobby knife.
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Old 08-27-2009, 01:46 AM
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Default RE: Flex shaft spacing problems...

so then the whole point of the ferrule is to brace the prop thrust on the flex shaft, not to connect the flex shaft to the prop shaft. Please bear with me, I am new to this whole flex shaft world. I just feel like I got mislead when I bought my new hardware.
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Old 08-27-2009, 02:48 AM
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Default RE: Flex shaft spacing problems...

Dont want to confuse you but they make a ferrule that is soldered to the flex shaft it has 2 allen screws to hold the prop shaft on to the flex. It uses bushing wiith a bearing in front at the ferrule and at the rear for when the prop loads onto the rear of the strut. My rigger is made this way.
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Old 08-27-2009, 07:15 AM
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Default RE: Flex shaft spacing problems...

Can you get a photo of your installation? What Unclecrash is saying is correct if you have an open ended shaft housing that goes from the hull to the strut but ends before the strut. In this case a ferrule is soldered on to the aft end of the flex cable and butts against the front of the strut. The prop shaft then goes through the strut and slides into the ferrule where it is locked in place with set screws. If the shaft housing come out of the bottom of the hull and attaches to the strut, then you have no ferrule. The prop shaft is typically designed with a hole in the forward end to accept the soldered or brazed in flex cable.
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Old 08-28-2009, 05:24 PM
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Default RE: Flex shaft spacing problems...

Hey everybody! Sorry this has been so confusing. I had my information all mixed up. The strut is a Dumas strut with a needle bearings. What my boat was set up with was a universal joint on an OS 46 max and what I was referring to as the "ferrule" was a brass tube soldered to the flex shaft. This was installed behind the needle bearings to prevent the shaft from sliding out. Since I'm gonna be using a collet, no more brass tube. I was wondering, The guys from my LHS set me up with some teflon bearings, flange reducers and some brass tube to reduce it. I was wondering, is there anything wrong with using the needle bearing set up?? The prop shaft is machined far enough so that the needle bearings run on a smooth surface. I can't see why I would go through the trouble converting... Sorry for all the confusion and thanks again guys!
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Old 08-28-2009, 08:33 PM
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Default RE: Flex shaft spacing problems...

I assume the teflon bearings are supposed to go into the strut to replace the needle bearings. If they are to put on the shaft in front of the prop drive dog as thrust bearings then I would suggest that you dont use them. The thrust bearing system works well with a square drive but not with a cable collet. As we have told you, there should be 1 shaft diameter gap between the drive dog and the strut. Without that gap, when the shaft "shrinks" under load it's likely to fail. I have used teflon bearings in the strut and also used needle bearings. Teflon tends to hammer out if the system (prop and shaft) is not well balanced. Needle bearings will eventually wear into the prop shaft if you are not diligent about lubrication. Choose your poison.
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Old 08-28-2009, 10:30 PM
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Default RE: Flex shaft spacing problems...

Thanks a lot for the great info! I have my plan and a much better understanding of the strut/prop shaft assembly.
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