electric motor bearing life?

Remember that air compressor I bought several years ago? one of the bearings on the electric motor went bad yesterday. New bearings (on order) were less than $10, and it was a fine excuse to go and buy a 20-ton hydraulic press, but I'm a little disappointed in the motor. Based on my sales figures since 2014, I'm pretty sure I have less than 100 hours of actual motor run time on this compressor. When I first started looking into it yesterday afternoon, the belts (there are two of them) weren't particularly tight. I've never adjusted the tension, so maybe they were tighter when new. If I was assembling this, I would not have made the belts this loose (point being that there sure wasn't much side load on the motor other than the drive-side tension required to turn the pump).

Are my expectations out of line? The motor is made by Baldor and uses sealed ball bearing units. Is Baldor known for using cheap parts? How many hours of run time is it reasonable for me to expect?

It's not unusual to need to tighten those belts after a break-in period. I recently went through that same process with a compressor we have at work.

Those Baldor motors are top drawer. I'm a fish biologist, and I depend on pumps to keep my fish alive. Over the years, I've used / installed / replaced a lot of of water pumps, etc.. Whenever a motor goes bad, if it's a different brand we replace them with Baldor motors.

It's anybody's guess as to why your bearing went bad. It is unusual for the bearing in the motor to go out, but it does happen.

My guess would be you got the minus 3+ sigma bearing from a relatively low ABEC rated bearing maybe coupled with just a bit of axial load that it just couldn't handle. The vast majority of that batch are great and a couple others prematurely die. WMBERG is my source for high (or higher) bearings when I've got to replace one.

Doesn't look like fun to service.

The installers never think of the poor service tech

Hard to troubleshoot over a keyboard but perhaps the belt tension was too excessive from the factory & that hasten the bearings demise (tho you didn't state which bearing went out).

Can't see the belt tensioning arrangement in any of your images.

Air compressor manufacturer's are notorious for having inadequate means of tensioning the belt(s).

New bearings (on order) were less than $10,

I hope it's not a case of you get what you pay for......

Sound too cheap.

My compressor is one of the most neglected tools in my shop. It's a Cambell Hausfeld 220V 6.5 HP motor on a 60 gallon tank. I bought it 20 years ago, and have never changed the oil or adjusted a belt. It just keeps chugging along. It gets light shop use unless I am using my bead blast cabinet. When I drain the water a couple of times a year, I get about two cups of white water. A few years ago I slipped hockey pucks under the feet and it made it noticeably quieter.

My guess would be you got the minus 3+ sigma bearing from a relatively low ABEC rated bearing maybe coupled with just a bit of axial load that it just couldn't handle. The vast majority of that batch are great and a couple others prematurely die.

Sensible. I guess somebody has to get the dud, and today it was me.

I made a note of the axial position of the pulley on the motor shaft before I removed it so that I could put it back in the same spot - but I will double-check the alignment with the pump's pulley when I get it all back together.

Doesn't look like fun to service.

 

The installers never think of the poor service tech

I installed it in this orientation because I as concerned about air flow (I didn't want the pulleys near the wall). As it turns out, access isn't so bad: the belt cage comes off with four quick-clips and four bolts, and then you have full access to the motor and pump.

Hard to troubleshoot over a keyboard but perhaps the belt tension was too excessive from the factory & that hasten the bearings demise (tho you didn't state which bearing went out).

It was the one closest to the pulley, but that bearing is also bigger than the one that's farthest from the pulley. so who knows...

Can't see the belt tensioning arrangement in any of your images.

 

Air compressor manufacturer's are notorious for having inadequate means of tensioning the belt(s).

True to form, there's no tensioning mechanism here. Shove the motor as far as you can along its slots, and hold it there while you tighten the hold-down bolts.

I did get cheap replacement bearings, which might not have been the wisest choice. But most of the hassle so far has been getting the press bought/assembled, and waiting for hollow steel stock to arrive from McMaster. If/when these new bearings crap out, I'll have already been through the process once, so a repeat performance should go pretty quick (and I'll use better bearings if it ever comes to that).

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I made a note of the axial position of the pulley on the motor shaft before I removed it so that I could put it back in the same spot - but I will double-check the alignment with the pump's pulley when I get it all back together.

 

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It was the one closest to the pulley, but that bearing is also bigger than the one that's farthest from the pulley. so who knows...

 

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True to form, there's no tensioning mechanism here. Shove the motor as far as you can along its slots, and hold it there while you tighten the hold-down bolts.

 

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Most likely shaft end bearing went out due to tension load.

Belt tension:

Excessive tension takes out bearings

Insufficient tension wears belts & (the smallest) sheaves

I use a piece of nylon string to check sheave alignment.

Must be long enough to span outer dimension of shelves 2x with a bit more.

I put the middle of the string perpendicular to the belts & then spin the compressor or motor sheave to carry the string into one or the other sheaves (outer side).

Then bring the string(s) to the other sheave to check to gap differences between the two sections of string.

Careful to miss the shafts and wide sections of sheave hub(s).

The compressors sheave is wider then the motors but it's the gap between each side of the motor sheave that needs to be the same (the string will show that).

Presumably the compressor is installed square to the frame so as long as the motor is square to the frame that aspect is good & all you have to do is draw back the motor to provide sufficient tension.

That's a problem as the belt tension will rotate the motor.

How I midigate that is to use shims under the trailing motor base.

I make shims from metal shipping strap cut a bit longer then the motor base.

Snug the leading edge bolts so the motor will move but not be able to pull up from the frame.

Leave the trailing edge bolts as loose as possible & put as many shims as you can under the trailing edge.

This rotates to motor shaft towards the compressor shaft thus reducing tension.

Pull the motor back and make sure it's square, then thighten the front bolts.

Remove rear shims as needed to a acheave the desired tension.

Make sure the shims are as far forward (against the bolts) as possible & thighten nuts/bolts.

When it's time to tension belts, remove shims as needed.

PLEASE keep all your fingers!!!!

I use a piece of nylon string to check sheave alignment.

Must be long enough to span outer dimension of shelves 2x with a bit more.

I put the middle of the string perpendicular to the belts & then spin the compressor or motor sheave to carry the string into one or the other sheaves (outer side).

Then bring the string(s) to the other sheave to check to gap differences between the two sections of string.

Careful to miss the shafts and wide sections of sheave hub(s).

 

The compressors sheave is wider then the motors but it's the gap between each side of the motor sheave that needs to be the same (the string will show that).

I got lost in there somewhere. Can you paraphrase this for me? Is this method better/easier than just using straightedges?

As far as tensioning goes, I plan to use a scissor jack between the pulleys; that should hold whatever tension I want (not a lot of tension, just a steady hands-free tension) while I lock the motor in place.

In my opinion, a piece of string stretched tight is about as good as it gets.

Place the middle of the string under the top half of the belts up against the compressor sheave @ the 11:00 position.

Turn the compressor sheave CW to trap the string between the belts & compressor sheave.

Continue to rotate until the string is @ 2:00.

Stretch both half of the string towards the motor sheave @ about 2:00 & 9:00.

Obviously the string will be flush with the compressor sheave @ 2:00 & move in/out until its flush on the 9:30 position.

With the string flush on the compressor sheave & extended past the motor sheave (left of it), even up the gap of the motor sheave/strings by adjusting/moving motor sheave.

NOTE that the clock positions are a guesstimate.

What kind of retainer does the motor sheave have? Tapered hub? If so, some trial and error (& interpretation) is required to dial in proper alignment.

As far as tensioning there are many ways to skin that cat.

You may even consider welding on some threaded rod connectors (long nuts) to serve as jack screws.

The motor will pivot CCW so need bolts @ right side of shaft end & left side of ose (opposite shift end).

Unfortinitly the motors base plate is too thin for this to work without some modification.

Permanent jackscrews may be a bit much considering the few times you'll likely need to adjust but would make adjustment a breeze.

In my opinion, a piece of string stretched tight is about as good as it gets.

Place the middle of the string under the top half of the belts up against the compressor sheave @ the 11:00 position.

Turn the compressor sheave CW to trap the string between the belts & compressor sheave.

Continue to rotate until the string is @ 2:00.

Stretch both half of the string towards the motor sheave @ about 2:00 & 9:00.

Obviously the string will be flush with the compressor sheave @ 2:00 & move in/out until its flush on the 9:30 position.

With the string flush on the compressor sheave & extended past the motor sheave (left of it), even up the gap of the motor sheave/strings by adjusting/moving motor sheave.

NOTE that the clock positions are a guesstimate.

OK, I got that. Makes sense; I'll give it a shot. Thanks.

What kind of retainer does the motor sheave have? Tapered hub? If so, some trial and error (& interpretation) is required to dial in proper alignment.

Straight shaft w/key; it'll allow for plenty of adjustment.

One thing I forgot to mention s if the compressor's sheave cooling fan blades stick out past the outer edge, put spacers of equal thickness were the string(s) make contact.

Neodeium magnets come to mind.

A tapered hub setup is a stronger arrangement then key/set screw but a bit more work to install as well as more costly to the manufacturer.