ST head bearing failure?

[rpg52]

I have a 12 Kw ST head, attached to a Detroit Diesel 3-71 (~80 hp).  It was sized to allow use of an arc welder.  The engine is so loud at 1800 rpm that it is nearly impossible to hear anything else, however, I was welding away yesterday, and thought I heard some additional noise(s).  I shut everything down, and when I felt the shaft on the back end of the head, it was warm enough that I didn't want to keep my fingers on it.  In the past it has remained relatively cool. 

Sound like incipient bearing failure to anyone else?  Soliciting opinions here.  I haven't done anything to the head previously, primarily because it is so heavy and hard to work on.  Seems like time to take it apart and replace the bearings (and do the Glyptal trt, as per Doug).  I had checked the grease before and it seemed ok.  Whaddya think?   
Ray

[jimdunne]

It is very easy to squirt a very small amount of grease in with a needle greaser, such as is used on ujoint bearings, etc.

 Shuts the bearings up instantly, sometimes for years.

Synthetic grease works very well, and do not over grease.

[Doug]

No amount of grease will fix that bearing once it becomes hot as you discribed.

Time to strip it.

Good quality bearings shouldn't be that expensive, so shop around and get a few prices.

You want a   C3 clearence 2z sheilded or 2 RS sealed. I like the the sheilded myself thats the highest level of protection a general purpose bearing needs from dust and dirt and they can be easily opened and repacked if needed, will pump greas into themselves from grease resivoir and are a little bit cheaper than the sealed.

Find a discount tool place and buy a stethiscope. when you have the new one in listen too it and feel the machine. Get to know what things should sound and feel like as part of your usuals PMs ( grease,oil changes looking for leaks ect ). if you use a machine a lot develop a feel for how often things like this fail and what sorts of changes you noticed so you can plan for a likely time to tear things open and replace/grease or otherwise service....

Doug

[jimdunne]

In the early  1970's, in Port Alberni,Vancouver Island, BC, we had a tub grinder, I think it was about 12 feet across, and ground spruce for pulp. The bottom bearing was always noisy, and we had to pump grease in it about 4 times per day to keep it quiet enough to stand. Noise;  it was only worse and worst!! Dad used something else with the grease, but i don't remember what it was. Knowing Dad, I guarantee the reason it was never changed was the expense of replacing it!

I don't think that bearing was changed out in at least two years of operating like that, and it was still being used when the operation was sold to the  the Price Co .  Can't remember  exactly when,, but it was around 1973-1975.

So I don't agree with the expensive notion of always having to change out a bearing with a little noise in it.

[Doug]

#2 graphite.....

Mixed with a heavy grease it will cussion a lot of sin.

In fact every DIYer should have a small can of the stuff for everything from guns to roler skates.

A company here in Canada used to market a brand of two cylce oil in the early 1960's called "Grand Prix" . It had a lot of much finer graphite in it and it worked well for the day.

Doug

Yes I have a new unopened can of the Grand Prix oil. Not for sale, some things you keep just because they are cool and remind you of people, places and times growing up

[ronmar]

Find a discount tool place and buy a stethiscope. when you have the new one in listen too it and feel the machine. Get to know what things should sound and feel like as part of your usuals PMs ( grease,oil changes looking for leaks ect ). if you use a machine a lot develop a feel for how often things like this fail and what sorts of changes you noticed so you can plan for a likely time to tear things open and replace/grease or otherwise service....

A mechanics stethescope is your friend in this case, By holding the probe on the case next to the bearing, you can realy get an idea of what that particular bearing is doing regardless of the other noise in the room.  Another way to do this is with a steel rod or long screwdriver.  With earplugs in, touch the end of the rod to where you want to listen and place some portion of the rod against the bone behind your ear.  this conducts the noise right to the ear drum while the earplugs cut out the ambient noise.  With ear muff type hearing protectors, hold the rod against the ear cup shell.  the cup will act like a spaeaker and you will be able to hear the audio conducted up the rod from the source.  The mechanics stethescope will of course have crisper/cleaner sound.

These things are great for listening to bearings, gear trains, valve trains, pumps, injectors, turbos and the list is almost endless.  They are particularly good at pinpointing the unusual noise in a really cramped engine compartment.  They are inexpensive, and my set is one of the most used tools in my shop. Harbor Freight usually sells them for a few bucks.  As Doug mentioned, it is one of the best ways to be proactive.  If you listen occasionally, you will get a feel for what sounds right and what has changed and might need looking at before it fails fully and perhaps takes something else with it like the shaft or rotor and stator of a genset. A good bearing will have a "hiss" that will grow in intensity and shift to a growl then a squeel as it degrades. Listen to a coulpe of different bearings in motors and such and you will quickly get an idea of what it is supposed to sound like.  It may also sound pretty good under no load, so it is good to listen to it as it normally operates under load if possible.

Ron

[Doug]

I'm glad you brought up the hiss.

I can't tell you what exactly your are hearing with the hiss but i do know that it will tell you a lot about the lubrication of a bearing and its condition. If hear the hiss change this means something is changing, maybe it just needs a little grease, maybe its trying to tell you the bearing is aproaching the end of its useful life. But its telling you something.

By the time you hear a growl its too late, metal is being sheared off and pits are forming. There is no coming back from a growl, your screwed. You can nurse things along and use lots of grease or Graghite to try and keep the growl from turning into a grinding noise but it s the change in that hissing noise that says HEY changes .......

I don't hear so well now but touch and feel also can tell you a lot about things. Try and move a shaft on a new bearing with a good fit on the shaft and housing. I can, on a good day feel the .003 clearnece on a C3 bearing. I can sometimes detect a change by trying to lift and move the shaft. A worn outer bearing housing in an end bell will cause no end trouble especial in a direct drive. An eg shaped bearing housing will also cause bearings to fail because that extra slack in the wrong places will actualy cause the races and balls to wear faster than normal and make things heat andthe oputer race to slip and move more.

Everything come back to good fitting shafts and housings, quality bearings, good lubrication and proper care.

Another name for a ball bearing is friction bearing, because there is metal to metal contact and eventualy wear

Doug

[rpg52]

Thanks for all the tips guys, really useful information.  I'll check out the bearing first just by turning and listening.  With the heat it generated, it seems likely to be toast though.  Incidentally, when calling around about Glyptal, the fellow I talked to strongly urged me to blow out the head with compressed air, followed by a xylene wash before applying the Glyptal.  He was concerned about sealing in any dirt that might be in the windings. 

I think I'm going to have to construct a solid work surface next to the head, hauling around the 340# of cast iron and copper down off the slope where it's located will be a bit much for my arthritic joints.    
Thanks again for the advice,
Ray

[Doug]

Another name for a ball bearing is friction bearing, because there is metal to metal contact and eventualy wear

Doug

I need to correct myself and explain things in more detail about this statement...
First as I wrote it that statement is wrong.

First a ball bearing is actualy an anti friction bearing, but what I was trying to get across is there is some needed metal to metal contact. You need some traction to prevent the balls or rollers form skidding ( this is a real probelm in lightly load truss abd TRBs ). Skidding causes uneven wear so you need some friction and contact but when properly lubricated the actual wear is so small its not a problem. Grease actualy bleeds out oil that forms a cussion between the balls and the race, keeps things clean by washing out the surfaces and preventing rust. When you cook a bearing the ballance between the tollerences ( in this case a .003) shrink, more metal to metal contact that is suposed to happen happens and the metal surfaces shed material faster than the thined out oil can handle. This increases wear and you can see where this goes. The Hiss you hear in a bearing is the tells you a lot about whats going on inside....

A true friction bearing is actual a bushing, soft metal on hard with an oil wedge in between, but there is little wear once the wedge has formed .

As for the cleaning before you paint. Use compressed air but at no more than 20 psi!!!!!!

[gpkull]

rs is rubber sided bearing why not steel sided. you must have goood hearing as a 3/71 sounds like any other 71 seris not happy unless screaming and beggin for more load as the exhaust decibels grow higher and higher plus the weed killing aspect of this breed which will never stop untill it does

[Doug]

The 2 Z bearings are the Steel sided ones.

I've said a lot lready on the subject and probably am repeating myself but I think the advantages of the 2Z make it the best choice. The fact alone that they can pump grease into themsleves as needed from a resevior in the end bell is probably the single most important factor. All they realy need an end bell with a grease niple and purge port to clean out the old bleed out grease and ocational cleaning of the inner bearing cap of used grease and oil ( if equiped ). Of course this means you have to watch how much grease you are using if you have a bearing you are going to grease and lube from a resevor. Too much greasing is as bad too and can cause bearing problems as well as smearing the inside of the machine with used grease.

How much grease you need to use and the type for the aplication are also important. Here's where we come back to the listen and feel thing. A ST head probably will only need 1 pump of grease a year at very most and maybe thats too much in some cases. If opted to not pack my end bell, for stand by use I will probably never need to grease my shielded bearings and will scrap and replace them if I notice a change rather than regrease.
In my case I guess I could have gone with the sealed type, but I wanted the option for the future incase I need to add a grease fitting because I have a problem and no easy access to replacement bearings.

But others may have a different take.....

[adhall]

Doug wrote:

As for the cleaning before you paint. Use compressed air but at no more than 20 psi!!!!!!

For the benefit of those who aren't aware of this danger:
Don't dry the bearing by putting a finger through the inner race of the bearing and spinning the outer race and balls by blowing air across the bearing. The bearing will spin up to high RPM from a relatively low pressure air stream. Without lubrication, the bearing may seize. When that happens, you will have the inner race trying to spin rapidly on your finger. This can cause serious injuries.

I have also heard that the bearing can spin so fast that it explodes. I have no personal experience or hard evidence to support that theory--but why take the risk?

What I do is hold onto both the inner and outer races so that the bearing can't turn. Then I feel safe drying the bearing with a low pressure air blast.

Best regards,
Andy Hall

[rpg52]

An update, clarification, and always, more damned questions!

So, I detached the pulley/belt, pulled out the brushes from the gen head --- listening with a stethescope, the rotor spins with very little bearing noise, no growl at all, even stops and spins back to the balance point.  Seems like the bearing(s) are fine (haven't looked at them yet). 

So, why would the shaft be so warm when I was using it?     Plan to pull it apart, add some fresh grease and reassemble, keeping a close eye on it in the future. 

Andy H., the previous discussion was about cleaning the rotor, etc. with compressed air before painting with Glyptal electrical paint.  The bearing was a different discussion going on at the same time. 

gpkull ---  yeah, I thought I imagined an additional noise, whether I actually heard something, I now couldn't tell.  The Detroit was screaming as usual, only 1800 rpm, but that is pretty much screaming.  I have a fairly good muffler, but the mechanical noise of those engines is incredible, esp. if you are next to them.  What did you mean by the weed killing aspect?  All the oil they slobber everywhere? 

So, the plan is to disassemble enough to clean and grease, then reassemble, and keep a close eye on it.  I guess the Glyptal will have to wait a bit.  I wanted to do a more thorough cleaning/painting, but the head is on a frame at about eye level, I'm standing on a slope below it.  To work on it would involve assembling a heavy tripod above it to lift it up, then building a heavy work surface below it.  I wouldn't hesitate to do it, but have some other pressing obligations (not the least of which is building a frame for a roof over the engine and gen head).  The head is so heavy, it really is a 2+ person job doing much of anything to it.  Will report back if I have anything of interest.  Thanks again.
Ray

[Doug]

If the bearing was hot something has happened.

Was the end bell (housing) also hot?

If it quiet now maybe you caught it before any serious damage was done.

Your going to have to look at that bearing closely and turn the outer race by hand and try and feel for any roughness. If you feel anything after its been repacked then you have a problem. It may still run a good long time even if there is some roughness but you will have to watch it close, feel for heat and listen for noise.

This is a prety big bearing so I would repack it with an NLG #2 moly grease ( generaly I perfer a # 1 myself if you were manualy greasing it with a gun but I don't think you have a niple or purge so a thinner grease is of no help. Also how hot is it around the machine? the #1 is more of a cold weather grease ). After repacking the bearing fill the end bell so its about 1/2 -1/3 full of grease meaning that once everything is back together there is still some air space for the grease to move around. The extra grease in the end bell will also provide some extra lubrication if things over heat again.

What brand of head is this?
You say it spins back to a balance piont?

Now a realy healthy sign, your head is out of ballance, this puts more stress on the bearings.

[rpg52]

Hi Doug,

The end bell was cool, just the shaft was hot.  I pulled it part way apart, enough to see the grease, which looked fine.  I could spin the bell on the stator shaft and everything felt smooth.  I added a bit more grease and reassembled.  I was going to pull the shaft end off too, but found a wasp nest in there and decided to wait.  What those wasps think about that cooling fan spinning at 1800 rpm next to them I don't know. 

The engine and gen head are just sitting out, under a tree, but not even a roof over them at this point.  (I've been covering them during the winter, plan to put a shed roof over them this summer.)  I got the head (a Fuking) before I got my Listeroid off ebay from ??sawyer?? , the fellow associated with George of Utterpower.  It does spin to a balance point, which seems to indicate the bearings seem ok, but that makes sense what you say about it being unbalanced being a not good characteristic.  At this point, I'm not quite sure what to do, the bearings seem fine, the balance maybe not so good but I don't feel very confident about trying to alter the balance to improve it.

I can talk to a fellow at an electric motor shop regarding the balance.  Is there much that can be done to improve the balance?  I'm pretty ignorant about the possiblities at this point.  The default is to just use it and keep checking the bearing to avert a disaster.
Ray