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Old 03-21-2015, 10:14 PM
jfw432 jfw432 is offline
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Driveshaft replacement?

The coupler on my driveshaft has some wiggle to it and has for some time. It's one of those things that has scared me a little but it has been working for years. Basically it looks like the interference fit between the driveshaft and coupler has worn and the set screws are more or less holding everything together. It's not totally the set screws because I can't twist the coupler on the driveshaft much by hand but I would imagine the torque of the engine would spin it if the set screws weren't there.

The driveshaft is straight and true. The middle of my driveshaft measures between 0.999 and 1.000. The shaft under the coupler measures anywhere from 0.997 to 1.000.

Do I need a whole new shaft and coupler or will just a new coupler do the trick?
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Old 03-21-2015, 10:21 PM
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mikeg205 mikeg205 is offline
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pictures would help.
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Old 03-21-2015, 11:24 PM
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Doesn't it have a key Way? I'd be amazed if a couple of set screws would keep it from twisting. Sound like it's .003" loose and shaft is worn. You could have it knurled and returned to size or sprayed to reduce the clearance but it's probably supposed to be .0005-.001 loose anyway so it can go on without any interference fit. Need to measure the ID of the coupling as it could be oversized as well.
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Old 03-22-2015, 12:13 AM
jfw432 jfw432 is offline
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Yes it does have a keyway as well and the key isn't shearing or anything but isn't that more of alignment that load bearing? I've never heard of a slip fit (loose) driveshaft and coupler combo as standard. The coupler is tapered very slightly. The aft side of the coupler is around 0.986 and the front side (flange side) is 1.006. My guess is the front has worn pretty heavily from being poorly aligned at some point in it's life.

Picture 1 shows the shaft and coupler separate.
Pictures 2 and 3 show how far the coupler goes on the shaft without heat and some persuasion.
Pictures 4 and 5 show how much wiggle there is when the screws and key aren't installed.
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Old 03-22-2015, 12:15 AM
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His boat is "other" so it may be a shaft system we are not familiar with. I know the MC boats I am familiar with use a taper and key or they use splines in the later models. I have no idea what the early boats used.
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Old 03-22-2015, 12:17 AM
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Quote:
Originally Posted by jfw432 View Post
Yes it does have a keyway as well and the key isn't shearing or anything but isn't that more of alignment that load bearing? I've never heard of a slip fit (loose) driveshaft and coupler combo as standard. The coupler is tapered very slightly. The aft side of the coupler is around 0.986 and the front side (flange side) is 1.006. My guess is the front has worn pretty heavily from being poorly aligned at some point in it's life.

Picture 1 shows the shaft and coupler separate.
Pictures 2 and 3 show how far the coupler goes on the shaft without heat and some persuasion.
Pictures 4 and 5 show how much wiggle there is when the screws and key aren't installed.
How much wiggle is there when the key is installed? That is all that matters.
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Old 03-22-2015, 12:28 AM
jfw432 jfw432 is offline
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Just enough to see that it is twisting but you can't really see the keyway edges getting mismatched.

Sorry, this shaft and coupler is more closely related to nautiques. I'd ask over on those forums but a lot of those guys recommend buying a new $400-$500 double taper driveshaft to replace a perfectly good old style shaft when replacing a prop so I figured I'd just be wasting my time asking them.
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Old 03-22-2015, 12:52 AM
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As long as your set screws keep it from coming apart, you should be fine. The key takes all the torque and passes it along to your prop.
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Old 03-22-2015, 09:56 AM
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Probably right and shaft caused some wear due to misalignment. Might want to measure runout on face of flange when coupling is on and sets crews are tightened to ensure it isn't worn irregular. If so, a macine shop would slightly reborn the coupling and restore the diameter on the short end so ~.0005 loose and it would be good as new. If flange checks out OK I'd just put some red locktite in the bore and reassemble to run it as is.
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Old 03-22-2015, 10:29 AM
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You need to get a new couple minimum-The coupler is supposed to be very snug on the drive shaft - If you can slide your current coupler onto your shaft and easily remove it.. it is worn.

this is a good watch.. there's another good video on this union.

https://www.youtube.com/watch?v=2ra-CapAQeg
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