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Old 06-05-2012, 07:59 AM   #21
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Originally Posted by jleonard View Post
I'd like to see some close up pictures of the failed parts. I designed and manufactured steering shaft u joints for 25 plus years and failures like that are rare.
Cardan shaft failures are not all that rare in marine applications. Alignment is just as critical as other shafts and careful attention to fasteners is important. It is not a "fit and forget" item.
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Old 06-05-2012, 08:11 AM   #22
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That assembly is a Cardan shaft. It appears that the pin retainers loosened or were never tightened properly when installed and were probably missing for some length of time until one moved out enough to create sufficient vibration to throw both out.

My guess is that the engine end pin left the scene first and the clunk you heard was the prop flinging the shaft around which caused the aft pin to depart. If it happened in the reverse order you might have had an even more exciting adventure.

This is a case study in why "checking" moving parts means to actually look at them and move them to make sure all the bits are in place and fastened properly.


something that is absolutely necessary...but I'll be the first to admit that long list of checks gets shortened with time...
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Old 06-05-2012, 08:21 AM   #23
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when I used to deal with cardan shafts used in Ag equipment the bearing cups were held in place by spring circle clips which fit into a groove in the "yoke". If the bearing cups were not pressed in completely the clip wouldn't seat into the groove and sooner or later the "cross" and shaft would come loose. Could be what happened here
I had never heard of cardan shafts being used in a boat, but it does seem to be an application which would make engine alignment less critical. A good thrust bearing would be required.

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Old 06-05-2012, 08:22 AM   #24
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I didn't know that had setups like that in boats. Mines a shaft with a huge coupling. The motor is positioned at a down angle and has a variety of shims. U joints would be nice. I would imagine you have a cutlas bearing? Might want to check that as well. I second some close up shots. Good post though.
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Old 06-05-2012, 09:31 AM   #25
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Shew! Close one, Mark. It sounds suspicious. I'd have difficulty believing it was a material failure of some kind. Likely, it was something that was missed in the final check. It could have been a real disaster if, like Rick B. noted, it didn't come apart as it did.
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Old 06-05-2012, 10:39 AM   #26
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This is a case study in why "checking" moving parts means to actually look at them and move them to make sure all the bits are in place and fastened properly.
Who would thought the universal joints would come apart? Seems the pins all came out. I am presently tied up at home for the next couple of days while a new heater and air conditioner is installed. Won't get back to the boat 'til the end of week.
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Old 06-05-2012, 11:30 AM   #27
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Who would thought the universal joints would come apart?
If it is made of two or more parts assembled by humans or machines and is subject to movement, vibration, temperature changes, or manipulation - intentional or otherwise - it will come apart sooner or later.
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Old 06-05-2012, 12:53 PM   #28
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That assembly is a Cardan shaft. It appears that the pin retainers loosened or were never tightened properly when installed and were probably missing for some length of time until one moved out enough to create sufficient vibration to throw both out.

.
Rick-- Are these pin retainers something that would normally be safety wired, like the set screws (bolts) on our shaft couplers?
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Old 06-05-2012, 01:58 PM   #29
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It is unlikely to be safety wired since there isn't much control over the weight and a Cardan shaft should be dynamically balanced.

It is probably an automotive or agricultural version the builder adapted to drive their boats. Some higher quality units use a two part yoke that is bolted to hold the cross or pins in place, some (as this one appears -only Mark can tell without posting one of his usual large photos) are budget versions that rely on the bearing retainers to hold it together. As someone else mentioned, a split ring and groove holds each bearing in place. Some use a cap with a single central bolt to retain the bearing and locate the assembly.
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Old 06-05-2012, 06:27 PM   #30
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Thanks. I can now visualize the components that are being talked about here (I think). Seems very odd that at the low rpms we're talking about here that the forces would be great enough to break them or throw them out of their housings.
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Old 06-05-2012, 06:32 PM   #31
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Who would thought the universal joints would come apart? Seems the pins all came out. I am presently tied up at home for the next couple of days while a new heater and air conditioner is installed. Won't get back to the boat 'til the end of week.

I can't visualize what "pins" you are refering to, is it the needle bearings from the cups?
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Old 06-05-2012, 06:35 PM   #32
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If it is made of two or more parts assembled by humans or machines and is subject to movement, vibration, temperature changes, or manipulation - intentional or otherwise - it will come apart sooner or later.
I would have thought "later" to be the operative word. The other year the U-joints in my 1987 BMW 635 were so worn out that they were allowing the drive shaft to move around enough to contact a heat shield mounted just above it. Obviously continuing to drive it this way would resulted in their complete failure. But I ws amazed at how messed up they coud be and still function. Which is why the failure of Mark's driveline is such a surprise. I assume it's still under warranty?
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Old 06-05-2012, 06:35 PM   #33
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Seems very odd that at the low rpms we're talking about here that the forces would be great enough to break them or throw them out of their housings.
My WAG, having only seen the parts in a picture smaller than an avitar, is that it was "infant mortality" and probably related to incorrect or incomplete assembly and has been failing for some time. It should be a warranty issue if there is such a thing on a Chinese boat.

Based on recent experience with another brand new Chinese built 100 foot trawler style boat, I wouldn't touch one with a 100 foot pole unless the importer has a very very good service department and is willing to send techs wherever the boat is at no cost to the owner.

I'll be delighted to tell that story as soon as the lawyers have filed the papers and it becomes public domain.
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Old 06-05-2012, 06:48 PM   #34
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I can't visualize what "pins" you are refering to, is it the needle bearings from the cups?
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Sorry, "pins" was my description of the bearing bearing (doubling intentional) cross piece.

Those units are just like normal universal joints for the most part but some have machined and ground "pins" that fit into the bearing cup that fits tightly in the yoke and holds the bits together.

Others use a bolt through the center of the bearing assembly and fasten to a stubby version of the cross. The outer end of that type of bearing forms a "hat" that seals the bearing and snugs up against the yoke.
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Old 06-05-2012, 07:32 PM   #35
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Sorry, "pins" was my description of the bearing bearing (doubling intentional) cross piece
Sometimes referred to as "spider" by the perfomance car and truck folks.
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Old 06-05-2012, 08:27 PM   #36
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A marine mechanic will visit the Coot Thursday to assess the situation. Builder will provide parts, including a new shaft section, if necessary. One possibility is that the shaft wasn't properly balanced or became unbalanced.
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Old 06-05-2012, 08:29 PM   #37
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Mark, did those joints have grease fittings or we're they the non-greased type? Curious...
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Old 06-05-2012, 09:07 PM   #38
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Ray, by the smudges on my hands, I'd say they're greased.
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Old 06-05-2012, 09:31 PM   #39
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Knowing how the tides can really move their your guardian angel was kind.
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Old 06-05-2012, 09:44 PM   #40
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MARK - - >

KEEP A CHECK-UP SCHEDULE ON EVERYTHING!

I'm very pleased this mechanical mishap worked out relatively OK for you. Here's to wishing you safe sailing days ahead!
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