Lister Engine Forum
Lister Engines => Lister Based Generators => Topic started by: BruceM on January 06, 2006, 11:30:21 PM
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My ST 3000 watt head makes a strange grrrr noise when loaded. It increases with load. It's loud enough to mask some of the engine mechanical noises. The unit does not run hot, and the output is good under load. I did not repack the bearings yet, but they feel smooth.
Any thoughts about the source of this sound? Could it be the "dog house"?
Bruce
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Could be either or both.
My doghouse was flimsey and falling apart, so I replaced it with a smaller good J box, and remote mounted the volt meter and pilot light, with a hobbs meter and the control rheostat (which crapped out and I disconnected) In a cool looking grey steel box on the wall.
Nonetheless, noises continued. I dismounted and disassembled the gen. The bearings were not damaged, but they did not have grease in them, in my opinion, they still had cosmoline preservative in them, that's what it smelled like to me. The hotter they ran, the drier it got. it was beginning to form a shellac like coating that I had to scrub off in gasoline or diesel fuel (standard parts cleaner around here). After that, I blew the bearings out with air, inspected them, and hand packed them with some good grease. They did not have bearing shields on the outside, so I didn't worry about overpacking. When I ran it again I just wiped up the excess that was pushed out the generator ends!
Oh, and my generator was rattling on the base. I engineered a slide so I could adjust it while it was running, but the clearance needed to allow sliding allowed a hellaceous rattle, so I had to build hold down straps as an afterthought (ugly spot!) >:(
Scott E
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Scott,
I'm glad to hear my genny wasn't the only one that leaked grease after I repacked the bearings. Thought I had broken a seal. Didn't recall seeing one, but figured there must have been something there.
First thing I did when I got my ST-5 was take it apart and remove and re-pack the bearings. Was planning to replace them, but they were of nice quality, so I left them in there. I have the Timken number so if they get rough, I can always replace them later.
As far as growling noise goes, that usually indicates either a dry bearing or one that is under an improper load, such as if the bearing is twisted in one of the end housings. The fact that the growl increses under load is consistent with a bad bearing.
Best thing to do is pop the ends off and inspect the bearings. Mine were packed with something that had the consistency of warm roofing tar. Very stiff creamy yellow goop. I washed the residue out with paint thinner and a brush, then blew the solvent out with air, then packed with moly grease.
Reassembled genny, then hooked it up to the dizzle. After running about an hour, I had about a tablespoon full of grease that extruded out one end.
The genny now spins easier and is silent except for a barely audible hysteresis hum once it gets up to speed. No mechanical noise at all.
Hope this helps.
Quinn
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Good Bearings are cheap by some Fags or SKF, avoid Nachi poor heat treating(as of 94 when I worked in the motor shops and used them in quantity). Get a C3 clearence bearing of course and in my opinion 2RS sealed are better. If you must use 2Z fill the inside of the end bell with NLG1 grease (Moly type not a bad idea). 2Z sheilded bears will to a degree pump grease from the resevor you made and lube themselves to a point.
If you like to add a greas fitting thats fine but also add a purge port so you can pump out the old grease when you regrease. Leave the purge port open and run the generator untill its warm to allow for expansion before you replace it. they could be to tight loose egg shaped...
The bearing manufacture should be able to provide you with proper shaft and housing size limits for the bearings I would check this before instaling new ones in case you have a problem. Or alternatively an EASA member electric motor shop will have proven dimensions for shaft size end end bell clearences.
When putting bearings on a generator shaft preheat the bearing in an oven to about 200-225 F(best do this when the wife is not home) it should slide on the shaft easy but be quick about it.
Never hammer on a bearing this causes brinelling and bearing failure. This much said you will most likely hammer on a bearing so make sure you only hit the inner race at least.
Over greasing is bad for bearings a couple of shots a year for bearings without a purge port is probaly enough...
Brushes.... thats a hole lot of information for me to type. In a nut shell ask the guy you got the head from for spares. Failing this make what you buy is meant for slip rings and not DC coms, although it not a huge deal they are different the slip ring types use a harder matrix more graphite than carbon black, Some have sinter copper in the mix..... Huge debate where I work over types of matrix mix and hardness...
Hope this can help
Doug
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Gentlemen, My sincere thanks for your sage wisdom and advice. I'll pull the bearings and check them out carefully.
I was hoping to get a 3KW PM generator from George B soon, he's got 120volt ones now, but I need the 220 volt which is still in the works.
Bruce
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If your going to pull them, scrap them (off the shaft that is)....
The force exerted to remove them always does some degree of damage.
Bearings are not expensive, in fact depending on how much you value piece of mind they are down right cheap.
Lastly remeber those cheap Nachi brand I told you about? I would be more comfortable using a crapy cheap new bearing than reusing a pulled bearing, especialy since we do not know how well the heat treating process was on the Chinese OEM bearings. The may have a soft inner or outer race who knows or overly brittle.
And remember what I said get the 2RS sealed bearing with the C3 clearence, no more greasing and no worries.
Doug
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Just an additional thought.
If you are wired for 240 and just loading one of the 120 legs, moderate loads will start dragging the head down.
Much less than 1/2 the rated current. When I do this my ST head starts making noise.
Jim
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Thanks Jim. I did have the "dog house" wiring set to 120 for load testing. That was well covered in the ST manual.
Bruce
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Doug, Can you suggest a web source for the 2RS sealed bearings you like best for this application?
I live outside a small town so not much is available here.
Thanks!
Bruce
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Honestly I don't know who you should see. I live in Canada.....
Acklands here sells bearings and they're owned by Grainger now maybe them?
A large auto parts chain may be able to help.
Perhaps you could check the SKF or FAG website for information. The good news is bearings are standard parts so any manufacturer can match a bearing to your needs. Your 3 Kva head should have something like a 6205 to a 6207 range no larger or smaller and these are verry common. The C3 clearence is almost standard and a 2 RS sealed bearing is also common (there realy are only 3 types the cheapest are the open bearings like you have follow by the metal sheilded type better and for your ap the sealed type).
I don't think you will have any trouble finding these.
Here's a thought any electric motor service shops, pump repair shops in your area? Most likely they will sell you some at a mark up or direct you to bearing suplier.
Doug
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Thanks Doug. I have a Grainger account so will check there first after mic'ing the bearings (if they have to be removed).
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There shoul be a number stamped on them....
Doug
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My St 12 kw head make a god-awful buzzing and growling racket if loaded (or overloaded) asymetrically (If you only put a 120 volt load on on the generator coils that is). You should keep the two coils in the generator somewhat balanced especially at high loads.
Twin ammeters is the key.
RB
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I pulled the bolts on the bell housing on the non-pulley end of my ST 3KW generator head and looked into the bearing. The grease is soft, new grease, not Yak lard.
I tried to pull the bell housing/bearing assembly off the shaft with no luck. I even made a puller plate of 1/4" scrap iron plate, screwing 3 6mm bolts in and using a 3/8" bolt to press on the end of the shaft.
All that accomplished is pulling the heads off the bolts.
How the heck can I get this bugger apart to replace these seemingly fine bearings???
Bruce McCreary
Metro 6/1
Snowflake, AZ
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Hmmm....
Sounds like there a little tight
Ok this isn't a nice way to do it and will muck up the bearings. First take a drill or punch and make some marks on the stator and end bell so you have some essembly marks. Remove your brushes. Whack the end of the shaft with a hammer and hard wood block (this should be the end with the cooling fan hard but if its not obviously the rotor comes out the back way) the rear end bell should pop out of the stator. Now try and wigle the rear end bell off this might not be easy but its usualy the smaller of the two bearings. Try tapping off the the front end bell with a chissle or whack the shaft the other way to knock the front end bell off. Now to remove the front end bell try and wigle it if this doesn' work hold the rotor with the end bell facing down and drop it shaft first ( about 2 to 4 inches no higher) on the hard wood block on a cement floor, it should drop
Always look at end bells face for screws indicating bearing caps and remove them.
If this doesn'twork you best take it too a machine or motor shop. Serious hammering or drops could mobe the rotor onthe shaft causing you much bigger problems.
There is no shame in taking one of these to a pro for service.
On third world engines the fit of machined parts seems to be prefered loose, on the third world electric motors the fit tends to be a little too tight. This is because the tollerences of parts aren't quite up to western standards, its a case of better a little too much than not enough.
Doug
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Thanks Doug!
I'm going to print out your note and go have another look.
Bruce
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How about posting some pictures as you go and if things start to bad stop, post, and wait. I'll make an effort to look in on this discussion a couple of times a day when I'm on shift ( why do I spend more time on the computer at work where I don't officialy have internet access??? )
Doug
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Doug- thanks for the instructions. I was able to drive the shaft and bearing out of the tight end bell using a wood drift and a hammer. Sorry to bug you again but you obviously know your bearings!
The small bearing seems fine (I'll replace both), but the larger one at the pulley end does have a spot that doesn't feel right, though that could have been from using a gear puller to get it off the shaft. The big bearing was not at all tight in the housing; your comments on clearances and China QC came to mind.
The Larger bearing is 6307-2RS (Made in China, seal on one side only), and Grainger has a double sealed NTN equivalent.
Question: The smaller bearing is 6305 ZX (Made in China no seals). There are two NTN bearings the right size- one has LL type seals, the other ZZ type seals. (Both double sealed.) Which should I get?
Bruce
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Sorry I thought I told you....
ZZ is the code for sheilded, dirt can still get in but the bearingis mostly covered and only open by a very small amount near the inner race. The nice thing about ZZ is you fill the cup inside the end bell with grease before you slid it all back together it will "pump" some gease into itself, but if that gears becomes fowled with dirt or water that could be a down side.
2RS is a fully sealed bearing, use it never grease, it and toss it when it gets noisy...
As far as the LL type in NTNs, I can't be sure what that means. I've nerver used a NTN there's nothing wrong with an NTN but I only use FAGs or SKF I know and completely trust them. I've changed what seems like thousands of motor bearing over the years and can only think of one case that FAG let me down, in the early 90s when somebody made a boo-boo at the factory and some were shipped with the grease in the 2RS lot.
Doug
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Thanks so much for help, Doug. I think I'll go with the totally sealed bearing. Here in AZ dust is the problem. (Brown air today from high winds, in fact. We need rain/snow badly, 81 dry days so far.)
Best Wishes,
Bruce
Snowflake, AZ
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You know I've never seen an ST head, but a rotating machine is a rotating machine. Whats not clear in the technical information is that these motors are manufactured to a eroupean metric frame size( IEC type as aposssed to NEMA T we generaly see ) we don't commonly use in North America. The ST-3 appear to a short frame version of the ST-5, they saved money by using the same tooling to build both. A 6207 main bearing is massive over kill for this ap by a factor of about 2 to 1. Just to put that in persective for you a high quality motor like a Baldor rated at 5hp might only have a 6205 ( just off the top of my head ). This is good it means it can take a much higher radial load a verry good thing in a belt drive system like this where you might have to realy crank the presure on the belts to keep it from slipping.
Oh ya and don't do anything like use lock tight to hold bearings on shafts or in housings it doesn't work.
Don't take a center punch and pean little dents in the bearing housing or shaft to try and make it tighter. This does work but it shortens the bearing life because it distorts the outer/inner race and causes rapid wear. There are tables to match bearing diameter and bell housing fitts but I'll be dambed if i can find them, ask your bearing dealer for this information and mic the shaft and housing if your concerned. If you do have a problem any good automotive machine shop can bore out the housing and make a steel insert for under 100 bucks that will never let you down again and shafts can be rebuilt using a process called sub arc welding and remachined (this is more expensive).
Doug
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RE: RE-building shafts---
I've re-built one of the early Chinese 5-ST experiments a couple of times. Both ends of the main shaft were undersized for the bearing and wore down even more so. I didn't sub-arc weld but did turn the shaft down and shrink on a sleeve which was then re-turned and ground for the proper fit. That's a job most maintenence machine shops can do for you.
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Thanks Hotater and Doug. I've got the new bearings and will install on the next decent day.
The bearing fit on the non-pulley end is too tight, and I"ll check the fit with the new bearing to see if I need the shaft turned. The big bearing to housing fit needs checking too- it was perhaps too loose.
The ST-5 head was not available when I had my Lister freighted. I wish it was as the ST-3 only has one set of brushes, not two. Because of my derated power at the 5600 foot running elevation, I think the ST-3 will be OK, and I'm still hoping to get a 240V 3KW PMG generator from George once that design is available.
Bruce
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My ST5 head growled. I took it apart and inspected/greased the factory bearings. I didn't see/feel any problems so reinstalled the original bearings.
Later on, after some experience with the head, I also discovered that if one leg is loaded significantly more than the other, it makes the noise. I also find it interesting that a given load plugged into one leg definitely makes more noise than the exact same load switched to the other leg.
Good luck and have fun!
troy