Knock in ST5

[lendusaquid]

Had the gen lined up quit well with the lister but iam getting a knocking sound  from the gen.I believe the rotor is moving back and forth as when i put pressure on the shaft end the knocking stops. So i misaligned the gen to put a slight force on the shaft to keep it at one end, the slip ring end. Some advise would be welcome as to whether this is acceptable or not. Also why use c3 bearings?   

[oliver90owner]

lendusaquid,

If there is a problem with your machine, it needs diagnosing and correcting.  Covering up a knock is likely to lead to early failure.  Excessive end-play may be controlled by shimming washers.  If you are axially loading your bearings and they are for predominantly for radial loadings, trouble will follow......

Misalignment can not be seen as good engineering pracise.  It might get you out of a jam but not satisfactory for normal continual operation, is my view.  If it needs thrust, it should have an appropriate thrust washer.

C3 bearings?  I know not why.  Presumably the manufacturer has deemed these to be the grade required for good running and longevity.  A closer tolerance bearing may tighten up too much depending on installation metals, housings, operating temperatures etc.  A looser fit would not, I would have thought, be appropriate for a generator.

Perhaps the alignment of the frame is so poor that closer tolerance bearings would be running  over-loaded axially?  Who knows?  This is a Chinese head, by any chance?

Regards, RAB

[lendusaquid]

Yes its a Chinese head. I was going to get standard bearings but read some threads from Doug talking about c3 bearings. So now ive got to find out which ones i need. Shims seem like a good idea but i better find out for sure first. Maybe a thrust washer on the slip ring end, and then it will bounce between the two. I am a bit concerned about the bearings wearing away the housings at the moment.

[Doug]

C3 bearings don't knock.

You shopuld be able to move the rotor back and forth axialy but it should tight and require some effort.
There should be a wavy washer ( spring washer in the back end bell that forces the rotor forward ).

Some motors and generators use shims to reduce end play but that requires set up at the factory and thats frowned upon these days you only want assemble once so wavy washer is the fx.

Quid I would recomend you strip the head down an check the bearings. They should roll smooth with no rough spots.
Get the bearing numbers and take the end bells to a machine shop and have the housing checked to see they are perfectly round and the correct size.
Already from your discription I as suspicios you have some bad machining and need a wavy washer ( that you can get from a motor shop, has to be the correct size for your bearings ) .

Most industrial/automotive machine shops have done this work before and can make repairs if needed shouldn't cost too much get a quote from several shops for a rebore and sleave of the bearing housings.

[MacGyver]

There should be a wavy washer ( spring washer in the back end bell that forces the rotor forward ).

Yes, my ST head has a spring washer in the back (brush) end to take up end play.

On the US side of the pond, they can be had from McMaster-Carr.
Goto  http://www.mcmaster.com and type in "wave washer" and pick your favorite size...

[oliver90owner]

lendusaquid,

I am a bit concerned about the bearings wearing away the housings at the moment.

The bearings should not turn in their housings.  If they are at all loose, you will need use something like 'loctite bearing fit' to hold them, or have the whole set-up checked out for alignment and possible remedial work.  You could drill, thread and grub screw to hold them but I doubt that is the best way to go unless there is a flat on the bearing outer to hold it properly.  Probably not enough spare metal in the housings either!

If I were buying a genny head I would be looking around rally auctions and picking up a couple of cheap sets with clearly(?)rubbish engines.  I reckon you are as likely to get a good old one than a good new one these days  (those buying chinese), especially if you know what you are looking for and are prepared to overhaul or mix'n'match parts.

Must be a greener way to go, as well, by doing a bit of recycling.

Regards, RAB

[Ian]

All 3 of the Chinese ST heads (from 3 different Chinese suppliers) in my possession have a (wavy) thrust washer ON THE FAN END and none on the slip ring end.

All the bearings as supplied were "standard" and NOT C3. I have replaced all the Chinese bearings with bona fide SKF standard bearings and they run just fine continuously without excessive noise or heat (at 1500 RPM or so).

The bearings are shrunk onto the rotor (front and rear) and the outer races are a good snug fit in the bearing housings. You should not be able to detect any end float by manually pushing and pulling. If you DO detect end float, then, as suggested earlier, you should apply some bearing "fit" as a minimum. If you can remove one of the bell ends without using a puller or a mallet, then the bearings are too lose in the housing.

Your knock under load could well be a cracked ball or race - probably on the fan end bearing. The only way to tell is to take the bearing out and inspect it. However, once you have the bearing out, in my opinion, you would be better to replace the stock Chinese bearings with a proper (standard) bearing.

I hope this helps.

Regards,
Ian

[oliver90owner]

The bearings are shrunk onto the rotor (front and rear)

Ian,

Surely they are pressed on , not shrink fitted?  If a bearing has to be pulled from a shrink fit shaft it will likely be toast and I would replace them as a matter of course.  I would only countenance re-using a bearing if it could be removed from the shaft by pressure only to the inner race.

It was Doug who recommended the C3 bearings, I believe.  I would have thought the normal tolerance bearings should be fitted....but you never know what the quality is like on Chinese manufactured stuff.  Might be better than some Indian tolerances....but a lot of experience from users has cast doubt on either making things close to absolutely right!

Regards, RAB

[mobile_bob]

ok fella's let me chime in on this one

on a ball brg/roller brg setup

the fixed element must be allowed to creep or turn
the rotating element must be tight and not allowed to turn.

as it relates to an st head

the inner race should be a tight fit on the shaft, it is the rotating element of the brg
the outer race should be a snug slip fit, it is the fixed element of the brg

if the outer race is not allowed to creep it will not allow the brg to distribute the wear evenly
and it will put all the loading on one side of the brg race continually leading to premature failure.

if you loctite the outer race it will not rotate, there would be no need for the wavy washer and
as the rotor heats and the shaft grows in length you will put end load on the brgs anyway, leading to premature wear
and failure.

cast iron has a looser fit than does cast aluminum, because aluminum expands faster and more than cast.

there are exceptions to this rule, some notable ones are pinned brg races found in some high torque applications, high speed applications
and a few others that generally do not have large side loads, or
where the cost of the housing is sufficiently high that it is more advantageous to spend the dollars on brg replacment rather than having to buy
very large and expensive housings.

in general though these rules apply, never loctite an outer race into a bore of a case, unless
you are trying salvage a worn bore, and recognise the fact that shorter brg life likely will result.

bob g

[Doug]

C3 Bearings have a little extra clearence and this helps a lot.
It lets the bearings move just a touch in case of a slight machining tollenrece and they are a high speed rated bearing so as they warm up the  .003 lets the internal parts move without binding when things warm up.

Some people disagree but I believe training courses and the small drums I filled with scrap bearings I replaced every month gives me some background on bearings in rotating electrical machines. This worked for me for years and years on small machines sitting on my bench to large enough to climb into. But if you can prove me wrong with some technical information or show me things have now changed and bearing manufactures have different specifications for rotating electrical equipment today not only will I humbly with draw my sugestion of the C3 but I will thank you for bringing me up to the new modern way of thinking.

Bob seems to agree and specificaly has corrected something I wasn't clear on. The spring washer is generaly ( but not limited to ) the back pushing the rotor forward. Machining must be tight enough to hold things from spinning but not so tight to allow easy movement on the other race to the end bell.
You actualy need to mic these things to be sure and check against the bearing makers specs for this aplication ( cast iron end bell electric motor ).

As I have stated before again and again touch and feel can tell you a lot everyone should be pulling, lifting on shafts and listening when the bearings are new and the machining is good so they can learn what is normal because if you stay on top if this when you do your inspections and PMs you can detect the changes before failure and damage to things like housing from worm out damaged bearings.
Touch and feel can't tell you much unless you are realy good and do this everyday several times on different machines or check runout with a dial indicators ect. You need a baseline of what is normal and you need to to an internal inspection and measurements ti find out if things are normal in the first place

Mechanical damage to a ball bearings makes for growling and noise, a cracked race will self distruct in no time flat.
The last time I saw a cracked race it was on a Nachi brand bearing ( cheap in my opinion ) and it cracked because I installed it incorrectly. The heat treating done to bearings mackes them very hard but the insides are still soft enough to make them very tough. Its very hard to say how well heat treated a Chinese Bearing is but you can be sure a cracked race would manifest itself in a very loud and angery way not a gentle knock. First material will spall off the bearing races followed by lots of heat and some vibration and noticeable up down slack. 

[lendusaquid]

The wavy washer on my gen is on the fan end. Pushing the shaft i have about 40 thou movement and then it clunks back into place. Wavy washer working i presume.I was thinking of using LOCTITE 641. Something thick,sticky and none setting maybe, any suggestions?.Since Doug seems to have alot of experience in bearings i will take his advise on using c3 bearings although i dont consider 1500 rpm very fast. The housings do seem to come off easier each time which is worrying.

[Ian]

There is some good stuff here. Useful and on topic (a pleasant change...). I have learned a few things too... Many thanks for the education.

RAB, I think in principle the bearings ARE pressed onto the rotor but I have never been able to get any of them on without GENTLY warming them through and then using a cylindrical drift on the inner race to set them on the shaft.

With regard to removing the bearings - the large fan end bearing is almost impossible to remove in such a way that I would want to re-use it. It is placed so close to the fan and the reach of the rotor requires that a very unusual puller will be required to operate on the inner race. Generally, the Chinese bearings are on VERY tight and I am convinced they shrunk them on at the factory. I have yet to remove one of these bearings without the aid of a hydraulic puller - and even then the hydraulic ram has been at its pressure limits before they give way with a "crack". As my pullers only allow operation on the outer race of the fan-end bearing (to reach the inner race, the fingers would have to be long and very thin) I would not want to re-use these bearings after the abuse I give them on removal.

lendusaquid, do you still believe that the knocking sound is the rotor moving axially ?

Regards,
Ian

[xyzer]

I pretty much agree with all points made......I would want to know why the lateral movement is being introduced. Is it a sepintine pully and is it running true? The wavey washer just stabilizes the mess and allows for expansion and manufacturing ease......Maybe?
Dave

[Doug]

How easy is easy Quid?

Can we drop the goofy nicknames?
You know I get phone calls from people and emails and I can't figuere out who I am talking too.

Get everything clean and dry if its covered in a grease and oil and have a look at the machining in that end bell. Bearing for this should cost you 10 - 20 pounds Quid so just go out and buy a set now. Sooner or later your going to need them anyhow.

Clean new dry bearing should be a snug fit in that housing if you have work to get it in place that would make me feel comfortable. I'm not telling you to hammer anything in here, this is a job for fingers and maybe a little light machine oil. If you can get that new bearing is and its a fit that tight but still has a little movement by hand that would be great. If it drops in with no trouble I might be suspiscious. If it feels like there are places that are tighter than others might indicate a machining issue such as an egg shaped housing or taper or too large and its getting cock eyed in the bore.

I have to be completely honest with you unless you have some experience with machining and how tigt or loose tollerences are suposed to be this is kind of like me trying to walk you threw setting up on your computer if you think windows are just something on your house.

As is I think it would be safe to say if you can easily compress that wavy washer by pressing the other end of that shaft and it springs right back without any real effort to move it ( other than spring tension ) it might be the sign of a machining issue. You say that end bell keeps gettting easier and easier to remove well to be honest you should have to wigle and work at it. Sliding it off again shold be easier than putting it on but you should still have to wigle and work at it some.. If your sliding that thing in and out on and off I would start to think maybe its time to get a machinist to check things out. Yes I know everyone lies to be self reliant here and do it all them selves but piece of mind that things are right is very cheap. Often you can get a machinist to look at this stuff for free if you show up with abox of Doughnuts and tray of Coffee .
In the UK maybe its tea and crumpets I don't know buyt its worth a try and the average machinist likes to look things over anyways before he quotes a price on a job and if you feed them they often will send you on your way if they feel you don't need their services rather than try and bill you for a look or trying to bring unneeded work into a quiet shop.

Another thing don't pester them if they are too buisy ask iof you can leave the parts there so they can look at it at their convinience. If the call comes back it needs rework tell them to do it at there convinience and make them understand this for a private person not a company and its a hobby things you are restoring an old engine and building a generating set. Explain the problem of the shaft slding back and forth and making the knocking sound too a little background always helps them. Machinists ( the good ones ) are prescision freaks and once they get in their heads they are doing a hobby job often the do better work because they apreciate the trouble that goes to rebuilding something just for the pleasure of it.

Pay your bills promptly and if all your troubles are solved come back again with more doughnuts and coffee so the next time you need something else they rememeber that nice bloke with the strange Chinese generator and Lister.

Some people will tell you you can cheat and lock tight or punch the inside of the bearing housing  ( dimple and usualy lock tight ) to holds things snug and this will be good enough. I've done this too and its cheating and in the long run will not help and infact will cause more trouble.

Lastly like all things on the internet take my advice with a grain of salt
"Since Doug seems to have alot of experience in bearings i will take his advise "
Untill you see me or anyone else change a bearing I'm just a voice in the night.

I wish I could offer more help than that
Doug

Ian I  jusrt read your post, I used whats called an Induction bearing warmer and heated all my bearings to 220-250 F. On a good day ( 95% of the time ) they just slide in place and shrunk on the shaft and this is the way everyone does it in an industrail setting. If you look in my put file you can see me doing the same things with a hot plate and mixed success.
There is some debate on the usefulness of pulled bearings. I have reused a lot of bearings that felt good before and after being pulled or pressed but some people ( usualy bearing people ) say the bearings are damaged and should not be reused. I never reused a bearing I had to heat to remove atthat point it is damaged everytime and the risk of overheating is always there.
I never use a hammer and drift, by that I mean I sometimes do but I have special ground and shaped chisels for that and if I am hitting an inner race its because I have been to slow sliding on, machining is too tight or questionable and I should know better but am going to do it anyways or I am doing small bearings 6207 and under and I am being lazy and doing it cold. I may tap hot bearing ( inner race in all cases ) to make sure its all the way home but thats the limmits of hammering.

I have hammered a lot of bearings off, this is cheating again and done for speed but be sure you can damage a gall a shaft realy esay like this.
My prefered tool is a 3 jaw puller and or a slide hammer ( if small ). Use a big wrench if you plan on reusing the bearings the hammering of an impact probably is not good for the bearing.

You can press bearings off shafts but when you put them on there is a risk that the rotor will shift on the shaft most smart people will not press a bearing on a rotor ( Back to the induction heater again and why we use it )
Its so easy to screw up a bearing by driving it in place I sugest you guys avoid it all cost

[Doug]

I pretty much agree with all points made......I would want to know why the lateral movement is being introdeced. Is it a sepintine pully and is it running true? The wavey washer just stabilizes the mess and allows for expansion and manufacturing ease......Maybe?
Dave

Best question of the day why the movement in the first place and yes tio stablize the mess.

Some companies like Asea went to a lot of trouble designing retaining systems to limit this slack without a spring washer. I chalk it up to beiing Germans and Swedes as to why they are so anal rententive most other compaines don't worry about. Another thing when underload and in use the rotor will tend to center itself in the core and float there not butting against one side or the other this is because the magnetic fields inside the machine will pull and hold it there so you don't want things machined to tight that it can't find this center float point. This is why Industrial machanics setting up big direct drive systrems with motors go to so much trouble to set up the shafts not just for alignment but to have that float and the centring of that float within the limits of the load and prime mover ( so the motor is not shuving a gear boxes end thrust ect. )