I'm rebuilding a 7.5 hp electric motor. Its shaft end bearing had a metal
seal away from the shaft end and was open on the other side. The other
bearing also had one metal seal and was open on one side. The motor has
zerk fittings for greasing.
I'm going to use this motor for an RPC idler motor only. I'd like it to
run as quietly as possible. In calling bearing houses, two different
clerks told me that electric motors often have two metal seals i.e. ZZ.
Should I use ZZ, 2RS, one side metal, or open? Why?
It depends on how you are going to use the motor, what type of
enviorment it is going to be in. For your application a sealed bearing
will work fine unless you are running it in a very dusty envoirment.
Then an open bearing with a zerk fitting to flush the bearing grease and
inject new grease is desired. There should be a pipe plug that you
remove opposite the zerk fitting so the old grease comes out rather than
pushing its way out along the shaft and creating a mess.
Z is better for dirty environments.
I guess you want a Z, because there must be some way to get the grease in.
ZZ and 2RS are greased out of the factory, so you could use them and ignore
the zerk fitting. If you only get a ZZ and need a Z, you can pry one
sealing out with a screwdriver.
If you have a metal seal it is most likely a shield. If you buy a
sealed or shielded bearing it is greased for life - the grease should
outlive the metal and relube is not required. Over 98% of bearings
never reach their design life and most fail due to over lubrication so
I would suggest that if you have a normal environment go with ZZ since
they are cheaper than sealed. If you are in a fairly dirty
environment, I would suggest going with NTN bearings with LLB non
contact seals. I would not suggest going with 2RS as these are contact
seals and create friction (drag and heat) and probably aren't
necessary. If you want to go with a single shield and relube, I would
suggest you reverse the bearing - put the shield on the lube side so
it will act as a meter. It will actually do a better job of keeping
the grease out of the windings than the way it was originally
Ignoramus22866 wrote in article
You would think so, but my experience proved otherwise.
I bought one of those ubiquitous $200 bandsaws from a local
Even though it was brand new, it had, obviously, been underwater at some
point.....perhaps in the ship's hold?
When you hit the switch, the noise it made was a cross between a klaxon and
a siren. My neighbors all knew when I was cutting metal.
As a part of my "Neighborhood Relations Policy", I would close the shop
doors if I had to cut something with that saw while working in the evening.
Since the machine worked fine, I tolerated the noise - hoping that the shop
phone would not ring while I was using it....since I couldn't hear the
phone ring, nor could I talk on it while the saw was running.
One day, I got fed up. I opened the motor up, took the bearings out,
cleaned them up, and packed them with a good quality (military surplus)
wheel bearing grease. They quieted substantially.
I took the bearing numbers, went to my local NAPA Auto Parts store, and
found the exact replacements (alternator bearings) in-stock......sitting on
the shelf......for less than $10.00 each.
I replaced them and the saw quieted so much, my neighbor from across the
street asked if I had bought a new saw.
Again, that was my own, personal, somewhat surprising experience.....YMMV!
The key here is "it had, obviously, been underwater at some point".
Yes, you put in new bearings, and the noise went down. That's what
Grant wants to do as well, put in new bearings. I just do not think
that the type of bearings will make much difference, noise wise.
Last month I did the same bearing replacement on a 7 1/2 HP motor for
my phase converter. As others have said, the difference in seals/
shields is minimal in this application.
I found bearings on ebay at 1/3 the cost from the bearing houses.
Dunno about that, but ...
Here's some old notes of mine on bearing nomenclature:
NTN (ntnamerica.com) (and others) bearing numbering system:
for more code interchange
Z = shielded one side, ZZ = both sides; ZS/ZZS = removeable, V/VV non-
steel shields, D/DD contact steel, TS/TTS Teflon.
L = sealed one side, LL = both sides. LB = non-contact sealed one side,
LLB = both sides. LU = contact sealed one side, LLU = both sides.
Suffix N = snap ring groove in outer surface of outer ring, NR = same
with ring supplied. FL/FR = flanged outer ring, R = standard, RW/FRW =
extended/flanged inner ring.
K = 1/12 bore taper on ID.
Ball retainer cages: J = pressed steel aka "ribbon" (assumed if
T2 = nylon, T12 = "plastic", G1 = machined, W = crown,
brass cage for cylindrical roller bearings or L1 = other bearings,
F3 = machined leaded steel, F5 = machined Cr-Mo steel, T1 = machined
D = OD, d = ID or bore, B = width, r = bore chamfer.
SRDG = single row deep groove radial bearing, numbers 6xxx.
SRDG cartridge (wider for more grease) = 63xxx.
SRDG max capacity (extra balls via filling slot) = BLxxx.
SRDG heat-treated high-strength long-life = TMBxxx.
Felt seal = 8xxx, Wide-cup felt seal = WC8xxx.
Angular contact = 7xxx, suffix G = flush ground for duplex pairing to
end play, suffix (?) C = 15 deg contact, D = 45 deg contact, none =
30 deg contact. Duplex pairing: back-to-back (higher rigidity) = DB
face-to-face (more misalignment tolerance) = DF suffix, tandem (added
in one direction) = DT suffix. Preload designations for precision
(using slight gaps in ring dimensions): N = normal, L = light, M =
H = heavy.
Double-row angular contact = 3xxx (extra balls via filling slot) or
5xxx (normal balls).
Double-row self-aligning angular contact (spherical inside of outer
= 1xxx or 2xxx.
Single direction thrust ball bearings = 51xxx, double direction = 52xxx.
Double direction angular contact thrust ball bearings = 562xxx.
Steel hardness in bearings typically 60 to 64 Rockwell C.
Radial internal clearance = C2 (best), standard (C or no suffix), C3,
C4, C5 (worst).
Last three digits of number XYY:
YY=ID: 00=10mm 01=12mm 02=15mm 03=17mm
X=OD: code for size depends on ID.
For ID 9mm or less, 3rd digit is ID in mm.
Bearing tolerance classification equivalents:
ABEC ISO DIN
ABEC 1 Normal P0
ABEC 3 Class 6 P6
ABEC 5 Class 5 P5
ABEC 7 Class 4 P4
ABEC 9 Class 2 P2
On Sat, 14 Apr 2007 16:42:46 GMT, with neither quill nor qualm, Lew
Hartswick quickly quoth:
Ctrl-A, Ctrl-C to grab all the text,
Start/All Programs/Accessories/Notepad to open Notepad,
Ctrl-V to drop the saved text.
In the Notepad menu: File/Save As, name it whatever.txt.
Rename. .eml to txt did you try that ?
I do some saving but often through a text editor. But directly has been done.
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.