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Thrust bearing built into the end of a shaft

52 Ford

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May 20, 2021
You ever seen something like this before?

I was modifying a Minn Kota trolling motor and had to take it all apart. When I was cleaning it up to reassemble, I noticed that the end of the rotor shaft had a ball shape in the middle. Upon further inspection, turns out it's actually a freely spinning bearing ball and it runs on a hardened steel disk at the back of the housing.
 
You ever seen something like this before?

I was modifying a Minn Kota trolling motor and had to take it all apart. When I was cleaning it up to reassemble, I noticed that the end of the rotor shaft had a ball shape in the middle. Upon further inspection, turns out it's actually a freely spinning bearing ball and it runs on a hardened steel disk at the back of the housing.

Do you mean like a direct drive turntable motor :)?

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Like a ball point pen. One single ball in the middle of the shaft. I'm not entirely sure how it's installed.
 
Yes. The clutch rod on a Yamaha Banshee, and presumably the RZ350s is the same way. A shitty design, IMO, as they have the tendency to become 1 with each other.

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Here's a picture of it. Excuse all the schmoo on the shaft. Its thick oil (It's freakin' cold outside.)

Damn well better appreciate it! Did I mention it's freakin' cold outside. :D

Seriously, though. Whatcha think? I tried to pull the ball out with a neodymium magnet, but it wouldn't come out. It IS a separate piece. I marked it with a marker and rolled it around. Definitely 2 pieces. Maybe it was swaged before turning? That or it's just stuck in there with a lot of suction from the oil I used.
2e9d91474ee9883fb63e8f9f51bdeb20.jpg
 
Yeah it's just a cheap, easy to manufacture thrust surface. Fairly reliable but not bulletproof. Sometimes they weld together - generally when they aren't kept well lubricated. Being what amounts to a point contact if it's just sitting on a flat disc as you describe they can generally break free again pretty easily even if they do lock up, but of course they will probably grind away at that point.

And yep, the most common place I can recall seeing the design is in the clutch of dirtbikes and ATVs.
 
Interesting. I got the trolling motor off another guy. It had been dropped or something. Messed up the top cover, broke the prop, and destroyed one of the steering bearings.

Turns out the metal thrust disk thingy that that bearing ball rides on was shattered. I replaced it with mild steel.

I lubed it with 85W140 synthetic oil. Probably not ideal, but it's what was in the oil can nearest to me :D

The oil does has some high pressure additives. That'll be good for the cripplingly high forces those bushings are going to undergo as I unleash all 45 FOOT POUNDS (not inch pounds or foot ounces!!!) of raw power to putt my kayak around in a lake.

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Here's a picture of it. Excuse all the schmoo on the shaft. Its thick oil (It's freakin' cold outside.)

Damn well better appreciate it! Did I mention it's freakin' cold outside. :D

Seriously, though. Whatcha think? I tried to pull the ball out with a neodymium magnet, but it wouldn't come out. It IS a separate piece. I marked it with a marker and rolled it around. Definitely 2 pieces. Maybe it was swaged before turning? That or it's just stuck in there with a lot of suction from the oil I used.
2e9d91474ee9883fb63e8f9f51bdeb20.jpg

Yup looks like a typical turntable thrust bearing :) Just a wee bit larger. Not a good design for high load and high speed. Over time the ball will nest itself into the thrust plate unless they are both extremely hard. In some versions, the ball is harder than the plate in some the reverse is true. I have seen anything from plastics like Thorlon and Nylatron thrust plates with steel balls to ceramic/carbide balls and plates. Wonder why they could not spend the buck or two for a roller or ball thrust bearing.

Typically you can see the wear on the ball if it is getting near the end of life. The worse I have seen had circular gouges, others just have a spot with a less smooth surface. The ball does not roll in the bearing it just rotates on the contact point. Hard to keep it lubricated in any position other than vertical where the lubricant pools in the bearing.
 
Ugh.
Nice looking comm bars....should have taken a skim cut on them when in there.
Works good if lubed....and right next to it is the comm, that does not like lube.....Let's hope you have back up propulsion to get home.
 
Ugh.
Nice looking comm bars....should have taken a skim cut on them when in there.
Works good if lubed....and right next to it is the comm, that does not like lube.....Let's hope you have back up propulsion to get home.


For scale, that shaft is 1/8" diameter.


Joking. It's probably around 3/8". Can't catch my fingernail on any marks on the shaft on the com bars. Looks worse than it is - maybe the lighting? Aughta be fine.

If the motor quits, I'll just scuttle the vessel and swim to shore.
 
Yup looks like a typical turntable thrust bearing :) Just a wee bit larger. Not a good design for high load and high speed. Over time the ball will nest itself into the thrust plate unless they are both extremely hard. In some versions, the ball is harder than the plate in some the reverse is true. I have seen anything from plastics like Thorlon and Nylatron thrust plates with steel balls to ceramic/carbide balls and plates. Wonder why they could not spend the buck or two for a roller or ball thrust bearing.

Typically you can see the wear on the ball if it is getting near the end of life. The worse I have seen had circular gouges, others just have a spot with a less smooth surface. The ball does not roll in the bearing it just rotates on the contact point. Hard to keep it lubricated in any position other than vertical where the lubricant pools in the bearing.

IT is pretty interesting how cheap they went with the bearing arraignment. I was expecting roller bearings throughout. NOPE. Oilite and this weird thrust bearing. Glad I didn't pay for the trolling motor - think this model was about $500 new.
 
For scale, that shaft is 1/8" diameter.


Joking. It's probably around 3/8". Can't catch my fingernail on any marks on the shaft on the com bars. Looks worse than it is - maybe the lighting? Aughta be fine.

If the motor quits, I'll just scuttle the vessel and swim to shore.

It's not really the size of it that I am looking at, rather the percentage of the bar
that is worn/rough.
Rough bars lead to brush bounce, and that increases sparking, leading to erosion of the bars.
 
It's not really the size of it that I am looking at, rather the percentage of the bar
that is worn/rough.
Rough bars lead to brush bounce, and that increases sparking, leading to erosion of the bars.
Since the wear is just radial grooves and not pitting or something like that, I don't see why it'd bounce

I do know what you're talking about. Like the brushes sparking on a corded drill.




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Since the wear is just radial grooves and not pitting or something like that, I don't see why it'd bounce

I do know what you're talking about. Like the brushes sparking on a corded drill.




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No problem, put a dial indicator on it and see what the runout is.
it maybe just fine.
 
No problem, put a dial indicator on it and see what the runout is.
it maybe just fine.
I'll do that.

Assuming it runs fine and I don't need to get out the ol' angle grinder and clean it up, and the rest of the parts go together as planned (mocking up the transom mount tomorrow) AND of course if the rest of the replacement parts get delivered in time, I should be in the water this weekend or next.

I'll update this thread and let ya know how she do.

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Some computer hard drives use that bearing arrangement.
Must be some TINY bearing balls in that situation. I haven't had a mechanical drive open in years. Think it was a 3.5" IDE drive. I can only imagine the spindles in 2.5" drives are even smaller.

By the way - hard drive platters make pretty decent mirrors! Gotta big hole in the middle, as long as you don't need to see your nose, it's pretty nice!

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