Converting a sealed bearing 1

[goodneighbor88]

I have been asked to convert the belt pulley bearings on a diesel engine (alternator belt) so that they may be lubricated as part of a preventative maintenance program. Even though the current bearings are sealed, the mindset is that if we grease them on a regular basis, they will last much longer.

It has been suggested that I add a grease zerk to the front dust cover, remove the front bearing seal and reverse the back seal to allow grease to flow out.

I have a few questions for the forum:

Does this idea sound like one worth pursuing?

Would reversing the bearing seal on the back of the bearing really allow grease to ooze out when the mechanic lubes the bearing?

If it does work, will adding too much grease cause the bearing to overheat?

Do I need to be concerned about mixing new grease with the original lubricant?

Did any other red flags go up when you read this post?

Sincerely,
Andrew Murphy

 

[EnglishMuffin]

Does this idea sound like one worth pursuing?

Depends on how long you want the grease to last. You can typically get 5-10000 hrs. If you have not had any failures I would think twice before changing anything. I take it that this is someone elses design and you are just modifying it ?

Would reversing the bearing seal on the back of the bearing really allow grease to ooze out when the mechanic lubes the bearing?

Probably not fast enough. Of course, it depends on how fast the guy injects it. And many bearing seals are not designed to be reversed so it might not even be possible (depends on bearing). There are also shields, which do have a small gap, but even these would probably not allow the grease to be evacuated fast enough. I think you would have to rely on having plenty of space on the grease nipple side, which of course depends on the design of the dust cover. Suggest you check with the bearing manufacturer.

If it does work, will adding too much grease cause the bearing to overheat?

Yes. Bearings typically cannot take grease volume exceeding more than about 1/4 to 1/3 of the internal free space. And after you have greased a bearing, it needs to be run at fairly low speed for a while to allow the grease to "channel", otherwise you will get gross overheating. The best bet is to grease during rotation.

Do I need to be concerned about mixing new grease with the original lubricant?

In some cases, yes. Some high performance greases do not mix well with other types and can produce a ghastly black mess. Again, you would have to check with the specific bearing manufacturer.

 

[rnd2]

It has to be assumed that you are having premature bearing failures otherwise such a modification would seem pointless.
Is it correct to assume other basic causal factors like alignment, belt tightness etc have been checked and eliminated as the problem, because providing more grease than is neccessary in these circumstances will not provide a "fix".
However, if the engine is operating in an environment that contains abrasive dust/corrosive materials and it is impractical to effectively prevent their ingress with seals then new grease, preferably continuously or at frequent intervals will be a big help as a regular out-flow of clean grease will prevent abrasive grit entering the bearing.

 

[diamondjim]

I would trust that the original
design engineer specified the
correct sealing arrangement for
this bearing. Too much lube is
not good and often you cannot
mix greases. The grease must be
compatable with the seal material.
If you are having early failures,
I would guess you are tensioning
these too tight.

 

[EnglishMuffin]

One other thing I would mention is that the seal discs incorporated into sealed bearings are quite delicate, and sometimes difficult to remove without damaging them. So even if what you are attempting is feasible or advisable, which I seriously doubt, I would obtain some spare seal discs ahead of time from the appropriate manufacturer. I once managed to get some for a particular make when I changed some bearings from shielded to sealed, but I was lucky - you won't find the part numbers for these items in bearing catalogs.

 

[JP0506]

Even after what eveyone suggested and what you plan to do, works, the biggest down fall I can see is the excess grease that is pushed out while running is going to ooze all over the belts causing slippage and belt damage. The bearing sounds like it is being overloaded and it will get extremely hot, you are asking too much of the grease, plus the chance of the dust cover popping out during operation would be high.
Suggestion : Try a different pulley ( what condition is the Vee of the pulley? If the belts are being over tightened is there room for a pulley that has another Vee? ) and if you have room try a double row ball bearing to take up the load.

 

[Warpspeed]

It seems to me, that the first pump of the grease gun is likely to blow one of the covers off the bearing. They are not made to withstand any great internal pressure.

Have you thought about running the bearing in oil bath instead of grease ? The oil reservoir could be vented, and the oil drained and replaced without any of the pressure buildup problems. Fitting additional external oil seals to an open bearing might be more easily said than done though.

 

[Tmoose]

I'b be trying real hard to harvest several well used/barely failed bearings. It would be interesting to see how the bearings typically fail.

If the seals wear out, letting contamination in, then re-greasing has something to offer. But so would inquiring about alternate seal materials.
If the bearings rum nuch over 120F, or the grease is dry or caked, then ordering bearings with fancier synthetic grease might double or triple life. without the hassle/danger of re-greasing. In my experience It is often possible to remove seals in-damaged with a dull penknife, which then allows flushing out the new/old grease (don't used chlorinted solvents), and re-lube with Kluber something or other.
If the failure looks like overload, then, like others have said, the belt tension may simply need to be controlled better.

 

[Gerry45]

On reading 'goodneighbors' post, I'm not so sure he has had any failures on the pulley brg yet. It sounds more like some bright spark within his company has decided to pursue a general program of reliability improvement, and the unfortunate pulley brg has been spotted as one of many candidates for possible modification.

The original post doesn't say who made the engine, but if its all OE spec from a 'reputable' manufacturer, my general suggestion is dont touch it. My reason.....

Alternator pulley brgs are generally rotating outer ring applications and this gives the grease a hard time because it is never able to escape the rotational cf. Generally greases under cf wont 'channel' easily and tend to loose base oil. To withstand this unusual operating condition, tensioner pulley brg greases are normally uniquely developed for the application. Apart from the obvious incompatibility issue, its quite likely that an 'off the shelf' grease (that would have to be used for relubrication) wont work very well in the high cf environment and give unpredictably short life.

Yes, automotive bits and pieces are built to a cost, but the are also quite well developed in many subtle ways. In attempting a redesign a system such as a pulley tensioner you could spend a lot of time 'reinventing the wheel' ! Generally engine accessories are made and tested to last the life of the engine, (although of course there is always the occasional early casualty due to manufacturing process variations !). If you therefore envisage running the engine well beyond a normal life span, and/or cannot tolerate any un-planned failures of the tensioner system, I would suggest that a more sensible form of preventative maintenance may be to replace the whole tensioner pulley at say 50% normal life expectancy. Doing things this way will mean no design work, no development time, no unexpected problems, in short no buggeration. Just a two hour task using established procedures once every 6 years or so.

...and if its not a rotating outer-ring brg application just ignore paragraph 3 but my conclusion will be the same !

Gerry.

 

[goodneighbor88]

Thank you to all who replied so quickly and by all means if you still have more to say, please do so. I will listen.

I understand everything presented here. I plan to approach my team leaders with some alternative suggestions. However, I would like to provide some additional documentation in my report other than simply citing this forum. Although I will give credit where credit is due.

Can anyone point me in the direction of published reports or a good source for reports that support any of the concerns brought up here? If you can at least point me the right direction, I'll be happy to hunt them down.

I am still haunted by my engineering professors who would not accept any citation from the internet. ;o)

Sincerely,
Andrew Murphy

 

[EnglishMuffin]

In my view, your best bet is to talk to some bearing manufacturers, although this is not always the answer to everything. The manufacturer who I personally think is the most expert in grease lubrication, and particularly greased for life bearings, is FAG. They also have some of the most sophisticated seals. In the US, they have merged with Barden, who also have considerable expertise in this area.

 

[Tmoose]

One place to get grease life calculation - but the chartw will be for super grease

http://www.bardenbearings.com/PDF CD/MACHINET.PDF

The hard-to-get SKF General catalog has re-lube intervals too, and are based on normal grease.

Bearing failure analysis -

http://www.bardenbearings.com/scan pdf/Bearing Failure Brochure.pdf

FAG has a real nice multi page one. I think it may be on their website but registration is required.

 

[Gerry45]

I agree with EM, you need to speak to the brg manufacturers. Unfortunately though, the vast majority of brgs supplied to the automotive world (particular small ones used in tensioners) are made by Japanese companies, NSK, NTN and Koyo. All these companies work with Japanese grease makers (Kyodo Yushi, Nippon Oil Co etc) to create the optimum lubricant for each type of engine accessory (ie alternator, distributor, ps pump, abs pump, throttle body, cooling fan etc etc). As these people are at the technical leading edge, for lots of obvious commercial reasons there's no way they are going to tel you about the performance of their products ! ** Since there's no substitute for actual hands on experience, any recommendations/advice from a non-supplying brg or grease manufacturer should be taken cautiously. On too many occasions I have seen stunning specification greases (with prices to match !) from prominent western oil companies fail abysmally against some obscure sounding lubricant used in a Japanese automotive component. Please dont make the same mistake.

** I think NSK do publish some quaterly Technical Journals in which they sometimes discuss their latest developments. Of course these are not really the 'latest' developments, but if you can get hold of some of these publications it may be of help to you. They may even be available on the net.

 

[MASSEY]

IMO reversing the seals will only make matters worse for the fact that most bearing seals are vented or at least designed to allow excess grease out of the bearing but another main function of a bearing seal is to seal out contaminants.

You should get a detailed drawing of your bearing and seal configuration from the manufacturer. It is likely if you reverse the seals that you will eliminate excess grease from escaping the bearing and at the same time 'vent' in contaminants - I don't think this is what you are trying to accomplish.