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Author Topic: Motor bearing replacement - when to change?  (Read 979 times)

Offline Dennis Toth

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Motor bearing replacement - when to change?
« on: October 31, 2021, 06:31:10 AM »
With electric not having any lubrications being feed to the bearings I am curious how long have people run them and had to change bearings? Are there different grades of bearing we could use (like ceramic) that would last longer and be worth changing to when the original bearings need to be replaces?

Best,    DennisT 

Online Ken Culbertson

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Re: Motor bearing replacement - when to change?
« Reply #1 on: October 31, 2021, 07:24:33 AM »
With electric not having any lubrications being feed to the bearings I am curious how long have people run them and had to change bearings? Are there different grades of bearing we could use (like ceramic) that would last longer and be worth changing to when the original bearings need to be replaces?

Best,    DennisT
If it is not out of line I would like to add the question of "When do you know you need to change them?"

Ken
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Offline Mark wood

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Re: Motor bearing replacement - when to change?
« Reply #2 on: October 31, 2021, 07:38:45 AM »
I usually replace mine whenever the impact causes distortion of the shield or roughness of the bearing.  <=

Otherwise if there is unusual noise present.

Periodic greasing could be done with a needle to force a bit of bearing grease under the shield. Or carefully removing the shield and adding a small bit. Doing that would make the life of the bearing very high.
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Why do we fly? We are practicing, you might say, what it means to be alive...  -Richard Bach
“Physics is like sex: sure, it may give some practical results, but that’s not why we do it.” – Richard P. Feynman

Online Dan McEntee

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Re: Motor bearing replacement - when to change?
« Reply #3 on: October 31, 2021, 10:34:31 AM »
   All bearings come from the factory with some sort of lubricating grease in them in a supposedly predetermined correct amount. If you have a bearing that small going bad, you will know it when it happens! Any excess clearance  that gets created will get magnified (it seems) and there are fewer balls to support the inner race and when it starts to go complete failure isn't very far behind. If something doesn't sound right, doesn't feel right or smells funny, stop using the motor and replace them. On certain types of bearing and applications, you can over grease a bearing, and cause extra drag and resistance. These small bearings need the correct grease, don't use what ever you got hanging around in the garage. keeping the clean is about as important as keeping them lubricated. You have cooling air flowing over the motor to keep it cool and there is enough junk in the air to get to small bearings over time. If new bearings are not that expensive for you, and you got a whole seasons worth of flying out of them with no trouble, and I mean hundreds of flights or more, just change them over the winter as a preventive maintenance measure. Getting the seals or shields off to clean and re-grease them is a tricky job to do it and not damage them where they can be reused again. If they are cheap enough, I wouldn't bother with cleaning and greasing, just replace them. remember, they are much smaller than anything most people have dealt with and they will wear faster. That prop is a lot of load on them as you go through the pattern.
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Offline Dennis Toth

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Re: Motor bearing replacement - when to change?
« Reply #4 on: October 31, 2021, 11:01:14 AM »
To replace them do you think it is worth buying an Arbor Press? Harbor Freight has a small 1/2 ton on sale for $62. Beside the press what other tool should you have to correctly change the bearing and the main shaft?

Best,    DennisT

Online Ken Culbertson

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Re: Motor bearing replacement - when to change?
« Reply #5 on: October 31, 2021, 11:42:03 AM »
To replace them do you think it is worth buying an Arbor Press? Harbor Freight has a small 1/2 ton on sale for $62. Beside the press what other tool should you have to correctly change the bearing and the main shaft?

Best,    DennisT
You have to weigh the cost of bearings and a press to the low cost of a new motor.  My experience is that the bearings outlast the motor but that will change as I check off all the stupid things you can do to ruin motors.  I have changed one set without a press....get the press!

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Offline Mark wood

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Re: Motor bearing replacement - when to change?
« Reply #6 on: October 31, 2021, 12:45:02 PM »
To replace them do you think it is worth buying an Arbor Press? Harbor Freight has a small 1/2 ton on sale for $62. Beside the press what other tool should you have to correctly change the bearing and the main shaft?

Best,    DennisT

Press fit items come out and go back in much better with smooth application of pressure. The HF press is a cheap POS but well worth the price of admission. In a small shop indispensable. I have one and a 2 ton one. The HF just sits someplace I'm not really sure of now.

As far as tools to go with your press you need something to drive with and support with. 3/8 and 1/4 drive sockets work quite well. Metal with holes in it work really good too. Doesn't matter a tremendous amount, just something sturdy that will support with a hole large enough for the item you are pushing or to go through and a drive small enough to fit in the hole. In the case of a bearing, if you wish to be able to reuse it after pushing on it you need a drive pin just smaller than the OD of the bearing race. That is when sockets come in handy.
Life is good AMA 1488
Why do we fly? We are practicing, you might say, what it means to be alive...  -Richard Bach
“Physics is like sex: sure, it may give some practical results, but that’s not why we do it.” – Richard P. Feynman

Online Dan McEntee

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Re: Motor bearing replacement - when to change?
« Reply #7 on: October 31, 2021, 12:49:11 PM »
To replace them do you think it is worth buying an Arbor Press? Harbor Freight has a small 1/2 ton on sale for $62. Beside the press what other tool should you have to correctly change the bearing and the main shaft?

Best,    DennisT

     If you have a drill press, it can be used as an arbor press for something as light as these bearings. Just make sure you have proper mandrels to fit the outer race of the bearings. Just do what you need to do to support the parts while you are pushing the bearings in so you don't stress and crack the motor frames. And arbor press is a handy tool and a lot can be done with them if you have the space for one. I used them all the time when I was working. If you are trying to tweak or straighten something, you can get a better feel with an arbor press than a hydraulic press. I would like to find one like my father in law had when we opened the torque converter rebuilding business. It had a threaded shaft on the arbor portion with a hand wheel, and you could raise and lower it with the wheel to keep the lever in a nice , comfortable  position. And he had all sorts of tools that went with it that would fit almost any bearing, seal, or what ever that I ever came across. But that is all overkill for these little bearings.. From most of the motors that I have seen, I would have designed the frames to take bigger bearings, and on the prop end, double that one up for extra support. If you have to keep working on something and pay a lot of attention to and replacing bearing a lot, I think something is under engineered. But that's just me.

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Offline Fred Underwood

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Re: Motor bearing replacement - when to change?
« Reply #8 on: October 31, 2021, 02:34:00 PM »
Cobra bearings and shafts are fairly snug.  A 1 ton HF press is makes it easier.  One of the videos by Lucien of Innov8tive recommended the 1 ton press for pressed in shaft for Scorpion motors, and Cobra seems similar. 

Good videos for shaft and bearings here
https://www.scorpionsystem.com/support/building_technic/change_shaft/#:~:text=How%20to%20Change%20the%20Shaft%20%26%20Bearings%20in,you%20risk%20damaging%20the%20motor%20in%20the%20process.

I had over 1000 flights on bearings in Cobra 3520 front mounted and then changed them because I had the motor out.  Rear mounting is harder on the bearings and they don't seem to last as long.  My use is on the standard Cobra bearings and their inexpensive Cobra replacements.
« Last Edit: October 31, 2021, 03:28:51 PM by Fred Underwood »
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Offline Dennis Toth

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Re: Motor bearing replacement - when to change?
« Reply #9 on: November 01, 2021, 10:39:37 AM »
OK yesterday I picked up the 1 ton arbor press at Harbor Freight for $62. I have a Bad Ass 2320 -820 that I had in a Ringmaster that got blown in boomed the nose. I rebuilt the Ringmaster but when I had installed the motor and spun the prop noticed that it was wobbling. Turning it over slowly by hand could feel movement of the shaft and a roughness. I call Invov8tive (who actually answered the phone) and they confirmed the bearing was likely flat spotted. I ordered the shaft and bearing and a second motor (just in case it doesn't go as planned).

When replacing the shaft and bearings can you apply some heat to the housing (I have high temp heat gun with a narrow nozzle) like we would do for IC engine bearing replacement? I assume one has to be careful not to heat the bell housing to much as the magnets are only glued in.

Best,   DennisT

Offline Fred Underwood

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Re: Motor bearing replacement - when to change?
« Reply #10 on: November 01, 2021, 11:34:02 AM »
I didn't need heat and used the video instructions from their site, noted above.  I can't answer your question about heat, but how would you determine too hot?  I found that the most difficult part was to loosen the set screw(s) to the shaft.  Get a good driver and consider replacing the screw with a longer one for reassembly.  Longer so the the driver has a longer insert and is less likely to round out.  Heat could help loosen the thread locker, but again, could be difficult to control.  Fortunately, you would be heating a small area on the end.
Fred
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Offline John Rist

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Re: Motor bearing replacement - when to change?
« Reply #11 on: November 01, 2021, 11:57:23 AM »
Ditto on the hardest part is removing the set screws.  I have rounded some in the past and had to drill them out. Gets real messy because the magnets collect the drill shavings. Then you have to tap for a bigger set screw.  When reassembly go very sparingly on the lock tight.  In fact I am not sure Lock Tight is needed.  Too much and the next disassembly will go poorly.    D>K

PS I have had good luck using a drill press in place of an arbor press.  Also a hard balsa wood block worked well as a pad to protect the windings.
John Rist
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Offline Fred Underwood

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Re: Motor bearing replacement - when to change?
« Reply #12 on: November 01, 2021, 12:38:17 PM »
After my friend started in his drill press and saw/felt how much pressure it was going to take, he declined.  That was the shaft on a Cobra 3520 series.  The one ton press is great, and I used on of the discount coupons so it was not expensive.

I made a block to keep the windings from contact.  Forstner bit worked for my size.

Try low strength thread lock on maybe two threads.  It seems to work, and the screws are still removable.
Fred
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Offline Mark wood

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Re: Motor bearing replacement - when to change?
« Reply #13 on: November 01, 2021, 03:12:28 PM »
Heat is the biggest help with loosening set screws. They're quite often put in with locker and the only way to get them loose is with heat. If you approach it slowly you will be fine. Apply heat for a bit, check, repeat. The screw is steel and the collar or housing is brass or aluminum, both of which expand faster than steel. The danger in the motor from heat is the magnets which can handle a fairly warm temperature. The lacquer on the wire can handle very warm temperatures, over 350 deg F, more than you can hold on to which means if you can hold on to the motor while heating it up, life is good. Blue thread locker, the most commonly used, will release before anything bad happens. Red thread locker has a higher temperature but I've not seen a motor using red, that's for when we need to be serious.
Life is good AMA 1488
Why do we fly? We are practicing, you might say, what it means to be alive...  -Richard Bach
“Physics is like sex: sure, it may give some practical results, but that’s not why we do it.” – Richard P. Feynman

Offline Mark wood

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Re: Motor bearing replacement - when to change?
« Reply #14 on: November 02, 2021, 03:39:48 PM »
If you need to heat the set screw, you could heat a red hot piece of wire and touch it to the set screw.

That would be the backwards way of doing it. That would cause the steel to expand creating an even greater tightness. It won't hurt the magnets to heat them to temperature well below their transition temperature, the temperature they permanently loose magnetism.  The neodymium magnets being used can tolerate up to 80C (180F) without damage. That's roughly what a person can stand to hold on to bare handed. The cure temperature for them where all magnetism is lost is 320C (600F) which between those two values its a matter of duration. I've done this quite a few times with no lost motors. Well, let's qualify that in terms of why I was using such procedure in the first place, which often involves some sort of elastic collision wherein the transport mechanism absorbed the majority of the energy. In such cases there is only gain to be had since the loss is already present. So, it's personal choice and my successes does not guarantee yours. In general the most a normal running motor should ever need is a small touch of lubricant and I doubt we get enough running time for that be truly necessary. There are plenty of other reasons to do it like making us feel better.
Life is good AMA 1488
Why do we fly? We are practicing, you might say, what it means to be alive...  -Richard Bach
“Physics is like sex: sure, it may give some practical results, but that’s not why we do it.” – Richard P. Feynman

Online Dan McEntee

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Re: Motor bearing replacement - when to change?
« Reply #15 on: November 02, 2021, 08:19:54 PM »
    In my work in the printing and binding industry as a maintenance tech, I had LOTS of opportunities to tackle small grub screws. My biggest enemy was operators not paying attention to little details like the condition of the tools that they use, among other things, and rounding out the cup of the screw. I would have to rebuild ink fountain key units on British Baker-Perkins web presses (about a dozen per fountain on an 8 unit double web press) and they had the worlds most bad ass loctite I have ever come across!! On really bad ones I would have to strip the unit completely down so I could get the smallest oxy-acetylene tip that I had inside to heat the gear that the grub screw was in. I eventually made a pointed tip for an 80 watt soldering iron, and put the point in the cup of the grub screw and held it there until the loctite softened. It took longer to heat, but at least I didn't have to take everything apart. The main object here is to burn off the locking material. If the cup of the grub screw was in good shape, I could remove them hot with no problem. It was just damn hard to hold onto the little boogers when they are cold much less when they are damn hot! So I just let them cool for a few minutes first.
   When it comes to these little grub screws, the fit of the wrench is important, obviously. I have found in both hobby stuff and in industrial stuff, the quality of the tool and the grub screw varies. I have the habit at work and at home to have several different wrenches or driver bits to make sure I have one that fits. If you are replacing grubs screws, pay attention to the end as to what kind it is. They can be knurled, dog eared or just smooth. And the cupped end of the grub screw should not protrude above the surface of what it screwed into. The top of the hole support the screw and keeps it from splitting, which happens pretty easy even on larger set screws. If the screw is screwed into a thin shoulder of surface, you can file or grind a flat spot or drill a recess for the end of the screw to seat in so the end of the cup is below the surface. A substitute for loctite, if the hole is deep enough, is to torque down the grub screw, then torque down another one right on top. This works pretty well and I saw it a lot in industry.
   Type at you later,
     Dan McEntee
AMA 28784
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