We recently had two horizontal 350hp,1200 rpm motors dissassembled and cleaned. The outboard bearing on one failed an hour after startup. The mech supr was sure they had added sufficient oil; the motor shop said there was "almost no oil in it". We of course immediately checked the other one and found the oil 2/3 up the site glass where it should have been. (Site glass tubing attached to the bottom of the sump, goes thru the site glass, vents from the top of the site glass to the top of the bearing housing)

A couple of weeks later, the second motor failed. Pulling the upper housing on the outboard bearing, the slinger was dry and the bearing sump contained almost no oil. The site glass still read 2/3 full; there was a 3 1/2" difference between the site glass and the sump (sump very low).

On the first one, I'm thinking air bubble or plugged line, but two in a row only on these specific motors? And no other inadequate lube failures in 22 years? Careful dissassembly of the site glass tubing reveiled no pluggage in bottom or vent or penetrations.

Any ideas? Thanks, Gordon, Livermore, Colorado

I am not familiar (yet) with these size of motors,
but do you have "forced" lubrication.
Is there some lubrication pump in the circuit?

quote:

The outboard bearing on one failed an hour after startup.

Things that come in my mind:
1)New kids on the block
2)Universal tool (pipe wrench)
3)Inventive spare (stock out)
4) Retirement (expertise has left)

The coincidence of two motors both worked by the shop and both failing in similar manner within short timeframe strongly suggests the same cause for both failures.

"Pulling the upper housing on the outboard bearing, the slinger was dry and the bearing sump contained almost no oil. The site glass still read 2/3 full; there was a 3 1/2" difference between the site glass and the sump (sump very low)."

You caught it in the act - the sightglass is not properly indicating the level. I think you agree that sounds like a smoking gun to indicate improper level indication (for yet-to-be-determined reason) as the cause.

"Careful dissassembly of the site glass tubing reveiled no pluggage in bottom or vent or penetrations."

If you did a static (shut-down) inspection and sightglass level is above sump level, there had to be some kind of blockage otherwise the levels would equalize. On the vent connection, is there a low point? Oil accumulation there could form a seal to prevent equalizing the top of the sightglass to the bearing cavity. I would be skeptical of this inspection concluding there was no blockage. Was it done by the same shop that repaired the motors to begin with?

20/20 hingsight, if you had the opportunity to do the inspection again. With bearing sump open (known to be at atmosphere) and with sightglass level above. To determine which is the culprit (bottom connection or top connection). Vent the top of the sightglass somehow (possibly by unscrewing the vent connection). If the level equalizes at that point then you know the problem was in the vent connection. If the level remains higher and you know the sightglass is now at atmosphere (same as oil sump), then there is no doubt there is pluggage somewhere in the bottom connection. I guess one more possibility to consider is plug within sightglass itself. Or even more remotely a discolored sightglass that made it appear there was oil where there wasn't.

The people doing the inspection had to verify at some point that the sightglass changed from indicating that incorrect level to indicating a level consistent with the sump, right? (otherwise they didn't confirm the level indication problem was even fixed after the inspection). At what point did the level stop reading incorrectly and what did they do to make it change? I would talk to the people who did the inspection and get more details on these questions.

This message has been edited. Last edited by: electricpete,

Hi !

Just a couple of questions !
1- What make of motor is it ?
2- How is the motor cooled ? Internal fans attached to the rotor ? Is it possible that the fans, if internal, have sucked in the oil past the inner shaft seals ?
3- Have you found traces of oil accumulated somewhere inside the motor ?

From what you have described, is it possible that when the bearing housings were filled with oil, the apparently defective oil gauges showed them full when they were not in reality ?

We, at ABB in Canada, when shipping new motors, we would brace the rotor with wooden beams to prevent undue movement of the rotor on the bearings and ALSO we would remove oil from the housing.

quote:

(Site glass tubing attached to the bottom of the sump, goes thru the site glass, vents from the top of the site glass to the top of the bearing housing)

Having a hard time visualizing how this is setup.

How does it:
"goes thru the site glass, vents from the top of the site glass to the top of the bearing housing"?
Is the site glass in a loop from the bottom of the sump to the top of the bearing housing, connected to both the bottom and the top of the bearing housing?

Could there be an assembly or other problem with internal clearances resulting in a pressure differential that could cause the oil to be misted out of the resevoir. Many clearances and fits are critical in maintaining the balance and direction of air flow in the motor.

Is there oil all over the bottom end and windings of the motor.

Invite yourself to the shop during the teardown.

Alan

I'm with Allan. The air flow inside the bearing at the site glass vent area could have created a local Venturi effect raising oil level in the site glass. It could have also mistified the oil causing it to escape through the seals.

Of course, this is an idea only. To verify it, swithching the vent into the atmosphere while running can prove or disprove it.

What kind of bearing is it?

There are two pieces of the puzzle.
1 - where did the oil go
2 - why didn't the oil level indicate low.

#2 is the more significant question imho. After all:
A - no matter where the oil goes (question #1), if operators saw the low oil level and added oil, the motor wouldn't have cratered.

B - Furthermore, if you answer #2 and confirm/understand that the oil level was indicating incorrectly, the answer to #1 may be easy: the oil was never added to proper level because the people filling the bearing were looking at an incorrect indication. If you really had lost a large amount of oil within the motor (I don't know how big this reservoir is), it would most likely be evident upon inspection (we all know how a teaspoon of oil can end up looking like a gallon).

"Pulling the upper housing on the outboard bearing, the slinger was dry and the bearing sump contained almost no oil. The site glass still read 2/3 full; there was a 3 1/2" difference between the site glass and the sump (sump very low)."

Hope I'm not sounding argumentative.

Is there the chance that gasket material blocked the oil sight glass inlet or outlet? Have had this happen when I worked in the motor repair business.

When the motors were shipped back (? assuming that the work was performed off-site) most repair shops empty all oil prior to shipping. If there was an issue with the sight glass from the final testing at the shop, then shipped without oil but with the appearance of being full. Babbett is quite porous and the original oil may have allowed for the longer life of the second unit.

Howard