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lost_cause
02-12-2015, 07:53 PM
As part of my teardown on the Millrite I just brought home, I tore into the motor today. When I tested the machine it was noisy at startup and I assumed dry bearings. After inspection I was proven correct - the top end bearing is completely dry and very noisy. The PTO end spins freely and takes forever to spin down, but it has the slightest noise and there is enough wobble between the inner and outer race that I think it needs attention too. Now it is just a matter of getting the right bearings, and that's where my questions are.

I remember once reading somewhere that bearings for electric motors have a different designation that conventional bearings. Is that related to the grease, seals, precision, or some combination of these? I've pulled the information off the bearings, but how do I know that what is in there is correct for an electric motor, and not just a generic bearing of the correct size? The bearings in the motor are as follows:

top bearing: NSK 77203
bottom bearing (PTO): Nachi 6204Z

Do I just go out and buy bearings that exactly match these, or do I need to look for something else? This motor is only a 1200RPM motor if that makes any difference.

lakeside53
02-12-2015, 08:11 PM
An "electric motor" rated bearing is usually just selected based on quiet running. For most intents, not an issue if you put in quality bearings of the same number. BTW.. Nachi and NSK are quality brands.

Are you sure the bottom bearing is a Z (single shield) or a ZZ (shield both sides?

The top bearing number isn't computing.. what are the measurements (metric)? That may be an old Hoover number and I'm pretty sure that would translate to a 6203ZZ

hornluv
02-12-2015, 09:28 PM
If you have a Motion Industries near you, give them a call with your bearing numbers. They'll either get you those bearings or be able to tell you the equivalent. 203 and 204 bearings are pretty common and should be on the shelf.

velocette
02-12-2015, 09:41 PM
Hi
Is this a vertical shaft motor Then the bearing MAY!!! be a 7203 angular contact bearing 17mm*40mm*12mm
Or a 6203 2RS
Be aware that this bearing also can have a 5/8 bore so take the bearing when you go to purchase new ones.

Eric

lakeside53
02-12-2015, 10:15 PM
NSK bought Hoover in the 70's and for a while overlapped Hoover numbering. If it's the Hoover number it's just a 6203ZZ radial bearing. Hoover would have put a -625 after their number if it was a 5/8 bore, but yes, be careful and measure the shaft at the bearing location.

JoeLee
02-12-2015, 10:22 PM
It doesn't really matter if you replace the bearing with a shielded or sealed bearing. I prefer the sealed to the shield for the simple reason the seals can easily be removed for greasing and the shields, well good luck !!! Nothing fancy or precision about those two motor bearings. I have found that some motor bearings have metric bores.

JL..............

lost_cause
02-12-2015, 10:37 PM
This is a vertical shaft motor. The currently installed bottom (pto) bearing is a 6204Z (I'm pretty sure it was labeled Z and not ZZ, even though it is a double shield). Logic would dictate that this bearing is taking the bulk of the downward force of the rotor, so should this be a 7-series bearing instead of a 6-series? Is there any reason why you couldn't put a 7-series in anyways? I found information about how the 4 digit bearing codes work, but how does a 5 digit code such 77203 work?

As I said, I don't know a lot about bearing codes, but how can some 6203 bearings have a 5/8" (16mm?) bore? doesn't the "03" indicate a 17mm bore? I'm going to measure everything before I order to make sure, but I think the sizes of the bearings sound correct. In my case it's not a case of going to a shop and comparing before I buy because it's too rural here to have anywhere within easy driving distance to get them. I'll more than likely ebay them and have them in the mailbox early next week.


Hi
Is this a vertical shaft motor Then the bearing MAY!!! be a 7203 angular contact bearing 17mm*40mm*12mm
Or a 6203 2RS
Be aware that this bearing also can have a 5/8 bore so take the bearing when you go to purchase new ones.

Eric

JoeLee
02-12-2015, 11:30 PM
The 6402Z is just a plain radial bearing. It will take a fair amount of side load meaning that the weight or load of the vertical armature is nothing.
I've replaced bearings in many vertically mounted motors and have never noticed any special type bearing in any of them, unless it was a special application.

JL.....................

lakeside53
02-12-2015, 11:36 PM
The 5 digit 77203 code is obsolete. It's now 6203zz. The 7's have NOTHING to do with angular contact. The "3" means 17mm, BUT can be overridden to be 1/2, 5/8, 12,13, 16 or anything someone in the USA wants.! 99.9999% (approximately!) of the 6203 bearings will be 17mm.

Just put in 6204zz. Don't put in a 7204 - never mind the problem with shields, you'll never get the preload right anyhow so it will be looser than a 6204!

lost_cause
02-13-2015, 06:49 AM
The 5 digit 77203 code is obsolete. It's now 6203zz. The 7's have NOTHING to do with angular contact. The "3" means 17mm, BUT can be overridden to be 1/2, 5/8, 12,13, 16 or anything someone in the USA wants.! 99.9999% (approximately!) of the 6203 bearings will be 17mm.

Just put in 6204zz. Don't put in a 7204 - never mind the problem with shields, you'll never get the preload right anyhow so it will be looser than a 6204!

ok, that explains why i couldn't find anything to explain that 77xxx code. i wonder if that means that the bottom bearing has been replaced once too? i'll order up a 6203zz & 6204zz today and that will be done.

macona
02-13-2015, 09:20 AM
Probably. It is pretty rate for mixed brands in a motor.

lakeside53
02-13-2015, 11:54 AM
ok, that explains why i couldn't find anything to explain that 77xxx code. i wonder if that means that the bottom bearing has been replaced once too? i'll order up a 6203zz & 6204zz today and that will be done.


Of course you will first measure the 77203 an make sure it's 17x40x12mm ;)

Rosco-P
02-13-2015, 02:09 PM
I'll more than likely ebay them and have them in the mailbox early next week.

YMMV. Needed bearing for a drill press quill, checked Fleabay. On Amazon, NOS Hoover bearings were cheaper than anything I could find on Fleabay (China import).

lost_cause
02-13-2015, 04:11 PM
YMMV. Needed bearing for a drill press quill, checked Fleabay. On Amazon, NOS Hoover bearings were cheaper than anything I could find on Fleabay (China import).

yeah, sometimes i'll check amazon, but for these it's hardly worth it. $12.63 delivered for both bearings (nachi - japanese made) from ebay.

Ohio Mike
02-13-2015, 04:27 PM
Be careful of "NOS" bearings. I gotten old stock bearings where the grease is all gummed up, they do have a shelf life. No reason not purchase new brand name motor bearings. I've had great luck with the Japanese Nachi bearings. Last time I priced them 6203-LL were $2.97, 6204-LL were $4.90, 6205-LL were $6.41 and 6206-LL were $7.70 each.

mbensema
02-13-2015, 08:52 PM
For future reference, you can use this site for interchanging bearings.

http://www.consbrgs.com/online_catalog.html

I'm in the middle of taking apart the motor on my Millrite as well. Before you reassemble everything, you might want to take a look at the top bearing on the spline under the spindle pulley. My motor bearings are dry, but don't seem to be that bad, but the top bearing on the spindle is failed and was causing the noise on my mill. That bearing is a New Departure 55507 which interchanges to an SKF 5207A-2Z or FAG 3207.2ZR.

Ohio Mike is correct on avoiding NOS sealed or shielded bearings, the shelf life on those is only a few years. The grease begins to separate at that point and it doesn't lubricate the bearing as well as new grease since the oil is coming out of the thickener and leaking out of the bearing. For the amount of work that goes into changing the bearings, the cost of new vs NOS is worth it.

lost_cause
02-13-2015, 09:15 PM
For future reference, you can use this site for interchanging bearings.

http://www.consbrgs.com/online_catalog.html

I'm in the middle of taking apart the motor on my Millrite as well. Before you reassemble everything, you might want to take a look at the top bearing on the spline under the spindle pulley. My motor bearings are dry, but don't seem to be that bad, but the top bearing on the spindle is failed and was causing the noise on my mill. That bearing is a New Departure 55507 which interchanges to an SKF 5207A-2Z or FAG 3207.2ZR.

Ohio Mike is correct on avoiding NOS sealed or shielded bearings, the shelf life on those is only a few years. The grease begins to separate at that point and it doesn't lubricate the bearing as well as new grease since the oil is coming out of the thickener and leaking out of the bearing. For the amount of work that goes into changing the bearings, the cost of new vs NOS is worth it.

i just pulled the quill and fine feed off the millrite this afternoon. I'm leaving each one of those intact until i get to the reassembly of the head. i've got a pile of degreasing, rust removal, and maybe even painting to do as i start to reassemble the rest of the machine. i've got a growing can full of small bolts & fittings already, so i decided to draw the line at dismantling the quill and downfeed.

when i bought the mill i did my best to isolate the noise and i was pretty sure it was in the motor, and it certainly is. the quill seems to be smooth, but it too is coming apart for a compete clean and degrease once i get to it. obviously i have no interest in replacing the tapered bearings on the bottom unless absolutely positively necessary, but the other bearings on the spindle are just ball bearings and i assume they are reasonably priced. if they are cheap and i have any thought that i might hear the slightest noise out of them i will be replacing them. that's kind of how it is with the motor bearings. the top bearing is completely shot, but i think the bottom bearing is actually fine, but since i've got it out and apart, i see the $7 for the bottom bearing as cheap insurance.

i went through the dry bearing syndrome a coulple weeks ago with an old grinder i have. it used to be my grandfather's and i'm guessing it's from the 50's - maybe 60's. it was tripping the gfci every time i turned it on so i opened it up to replace the cord & clean it out. the bearings turned one notch at a time because of rock hard grease between the balls. luckily the were single shield bearings, so i used a pick and cleaned out all the old grease i could and put new in and now it works like a charm. this has made me think about any of the visually ancient nos bearings i see for sale, but in most cases the new ones aren't more than the nos ones.