the Thrust Bearing: what holds it in?

I try to show how the thrust bearing is attached to the engine cases and the rotor of the J79 / LM1500 gas turbine engine.
Some whiteboard drawing, some real parts, and hopefully some detailed discussion of the thrust bearing installation in the engine we work on all the time here at S&S Turbines.

[@zczvcb]

This video completes my 8 hour Lessons in 10:00 mins. True Spirit of Engineering .

[@dikeshkurre6869]

Which branch of you are learning

[@leeleslie6615]

if you have a aero engine, you could complete your study by yourself

[@TuffBurnOutTeam]

I have noticed in all your video's you have lots of care in what your doing And there very in depth in what you do to with them Thank you for sharing Very very interesting in what you say about every thing AUSTRALIA

[@markwhitson]

I'm studying aircraft maintenance right now--and this stuff is so helpful to see. Thanks so much for posting these videos. Best regards from Toronto.

[@zyf6136]

Love this guy help me a lot on my turbine exam

[@eracismm]

Wow.....what a great job on the video an a solid explanation of how to mount the bearing on the shaft, and you showed the manual......Geez, it's true, heroes don't always wear capes........"it's what ya learn after you know it all that matters"....I'll never be there.. Thx again....

[@AgentJayZ]

Thanks for the kind words!

[@AgentJayZ]

There is always load on the thrust bearing. There is actually more rearward force on the turbine than there is forward force caused by the compressor "pulling". Most of the thrust from the engine is created by the exhaust nozzle... that's why it is there. The whole compressor - turbine system is just a gas generator to provide mass flow for the nozzle to accelerate, and produce thrust.

[@Daluke61]

"Space-age Van"... oooweee! Jet engines have always fascinated me. Over the years, I picked up a little knowledge here and there (thank you Google) but until I stumbled on this site, I had so many more questions than answers. Thanks so much, Jay. This is the best!!

[@Gooperdevil]

Hello! I´m Brazilian´s student. Thanks for the videos posted. This will help me a lot in my learning about aircraft maintenance.

[@AgentJayZ]

Can't think of any. What I refer to as a catastrophic failure would cause the engine to come to a violent, screeching, grinding stop. All rotating parts destroyed. So expensive to fix that it probably wouldn't be. The engine would be scrapped. A few pieces might escape the cases, but that's not an explosion. We haven't had any failures in our test cell since I started working here.

[@blampa]

Absolutely brilliant and informative as usual. I positively love your work, so much so I have decided to try and get in to the same field.

[@tek4]

How did it go, did you do the thing?

[@AgentJayZ]

For the rotor when building it up on a stand: 0.010" When it's in the engine and supported by the #1 bearing in front and #2 bearing in the rear: no measurable runout.

[@AgentJayZ]

There is a fancy tool that engages the splines inside the compressor shaft to react against the torque applied to the nut... but I've never seen it. We use the inertia of the rotor and torque the nut against that.

[@AgentJayZ]

Yes, it's a fan blade from a CF6-6, the first model of that engine. It's the one we had outside in the driveway for a couple of years. There are several videos I've made recently about that engine, and a couple I made almost two years ago.

[@deSloleye]

It is an amazing balance of things going on, air goes in, but then it goes out even faster. I guess the tension between turbine and thrust bearing is the same as with centrifugal compressor jets, and would be part of why the axial jet didn't take long to be developed after the centrifugal ones started working. How they work mostly makes sense, how they hold together is another problem altogether.

[@AgentJayZ]

The shaft has threads on it, onto which a large nut goes... during engine assembly. The arrangement is a bit different than the usual, straightforward thing we see on the LM1500.

[@AgentJayZ]

Yes, you have it. look at the strength of those ( solid stainless steel ) pieces stacked up. The most lightly built pieces are the air seals, and I bet they could hold up over 200 tons of axial load... I'm sure of the whole stack, the weakest link is the load capacity of the actual bearing, and it is huge.

[@AgentJayZ]

Those projections on the blade in the background are mid-span shrouds, and they are for support. Newer turbofans don't have them, so modern blades must be stronger and stiffer. Elaborate? I don't recall seeing any ceramic coatings in this video, but they are used as thermal barriers, reducing heat transfer.

[@AgentJayZ]

Oh, yes, now I see what you're saying. There are tapered roller bearings that handle large axial loads, but they are not used in turbomachinery as far as I know. Maybe they are not as able to handle the high speeds as well as ball bearings.

[@Nitinkumarbhalavi]

thank you so much to providing practical knowledge.

[@DScottDuncan]

Just reviewed this video on the computer instead of the TV...had to comment & 'like'! Darren

[@deSloleye]

Rightyo, gotcha. There's still that bit of magic about which part actually pushes that air down that thus must push the aeroplane forward.

[@FrontSideBus]

Now your just teasing us with that fan blade... Very good video once again!

[@gizmothewytchdoktor1049]

although i live on planet automotive i find this fascinating. thanks for taking the time to do this. =dok=

[@lucianosr71]

thanks man I have no idea how its works thanks for your time ,is a plasure to see this,my dream is work with engines like that

[@AgentJayZ]

A Sweeney Torque multiplier is a wonderful thing...

[@AgentJayZ]

To call them true seals is a bit wishful. The idea is to try and keep oil and air from passing through a gap between a stationary surface and a shaft spinning at 8,000 rpm.The carbon oil seal is a smooth surface of slippery carbon sliding against a highly polished mating surface. It leaks a tiny amount of oil. The air seal is actually as tight a gap as can be made without the two surfaces touching, so some air always gets through.

[@ToyotaKTM]

I found the answers in your "Heat & Gravity" video.

[@deSloleye]

Well in an engine already running at a stable rpm, I'd be inclined to think there was no axial load on the bearing. Drag from the turbine would equal thrust from the compressor. If the engine is accellerating, though, thrust from the exhaust nozzle would be higher than thrust from the compressor, so the turbine would draw back and the axial load would be towards the rear. If you reduce rpm, the thrust from the nozzles would reduce, drag on the turbine would reduce and the load would be forward.

[@dikeshkurre6869]

Good explanation and thanks to you

[@AgentJayZ]

Well, you are delving into black magic here, and there is serious debate amongst the technical people as I mentioned above... Everything is turning except the outer race of the thrust bearing; that is attached to the engine midframe, and the stack shown in this video is attached to the compressor rotor. The engine, however it produces thrust, transmits it to the aircraft via the main mounting points shown in some of my other, recent videos.

[@AgentJayZ]

Thanks !

[@AgentJayZ]

All of the axial force is taken by the thrust bearing. That's what it's for. The net force on the compressor-turbine assembly: now that's one of those deep dark secrets known only to the members of the jet people inner circle. A hotly debated subject.... what's your opinion?

[@AgentJayZ]

Ah, another ambiguity in the terminology... actually I mean the portion of the engine after the turbine that is shaped to accelerate the gases to produce thrust. It's only variable in afterburning enignes. It's not the clearest system, but exhaust nozzle is completely different from turbine nozzle, as well as the slightly more obvious "fuel nozzle"...

[@deSloleye]

By "nozzle" you mean the nozzle just in front of the turbine or the one downstream from that (the variable one on afterburning jets)

[@GeofreySanders]

Beautiful... who else would use a jet engine to hold up a whiteboard. : p

[@geonerd]

Cool, thanks! Not that it matters, but at 2:35 I think you got the rear air seal stacked upside down. :)

[@deSloleye]

Awesome thank you for that! That answered a lot of my questions from last vid. As usual, have more: I've been wondering what the predominant direction and size of the load is on that bearing. The compressor would be trying to exit from the front of the engine because it's thrusting, the turbine would be dragging so would be trying to leave from the back. The shaft would be under huge tension as well as torsion, how much axial force is borne by the thrust bearing?

[@deSloleye]

Of course there is a net work being done and force applied somewhere through the engine to shift all the air backwards. If there's no axial force on the shaft at constant rpm then I'd say thrust came from the diffusers/combustors, but they don't look quite THAT strong. So yeah... I'm definitely not part of the jet people inner circle. Do they have a cool handshake?

[@AgentJayZ]

Oh, you're smarter than you think you are. The jet engine is all very counter-intuitive. That's one reason it took so long to invent, and so long to develop after that. It seems to be either impossible, or to work by pure magic. Here's a hint: the thrust bearing is not what the engine uses to transmit its thrust to the airframe. It's only called a thrust bearing because - like all thrust bearings - it handles axial loads.

[@donnabeaudin5295]

crazy it looks like a giant bicycle head set bearing assembly

[@AgentJayZ]

Donna, you are exactly right. A bicycle headset bearing assembly is (usually) a deep groove ball bearing that acts as a thrust bearing. The main difference is the rotational speed. In a headset it's minimal, as opposed to a turbine engine, where it is generally thousands of revs per minute. A more suitable bearing for heavy axial (thrust) loading at low speeds is the tapered roller. Motorcycles went from ball bearings to tapered roller bearings in the headset because of their greater load capacity and resistance to brinelling... or denting of the races... called indexing by bicycle types... Aren't tapered roller headsets used in the high end bicycles? I think they should be.

[@donnabeaudin5295]

Hi Jay! Thanks for responding, I'm just using my bosses' you tube account at work, don't tell her I was too lazy to log out! lol I'm the master bike tech here at our bike shop and you are correct in that tapered roller bearings are being used on contemporary bicycles for headsets. Bottom brackets and wheels use roller bearings as well. The traditional conical race/ ball bearings ("cup and ball") are still in use today as well on more inexpensive bikes. As an aside i have found a use for many bicycle parts on some of my home made gas and tesla turbine projects...I just need to make a gas turbine bicycle and i'll be in heaven! (unequivocally no doubt). lol Check out my channel at drs2100 if you like! :D

[@AgentJayZ]

Exactly... or something like that. I'm not exactly sure. Nobody else is either... There's always a small element of magic involved.

[@motormouser]

Brill! Keep'em coming.Thanks...

[@sandycosmos1155]

Hi Agent Jayz, thank you for all these great videos that you've done so far. I'm wondering 1 thing here, is there any control to ensure that the upper part of the inner race doesn't pinch and/or damage the balls during assembly? Thank you again I'm especially enjoying the videos the ones are about T58 mounted boats!!! Also could you please share a video about assembly/torque procedure of the mainshaft nuts the ones keep the rotating materials together during the engine operation?

[@AgentJayZ]

The inner race halves are constructed so that when they are tightly held in full contact by the retaining nut, the groove matches the balls perfectly. The risk is not that they might squish anything, but that they are not completely held tightly together, in which case the bearing would be loose, and would likely fail in service. I've got a video about the main coupling, and one called what holds it together...

[@MPCapricorn]

Great Jay! :-D Thanks for uploading. a bit OT: Can you tell me what the accepted tolerences are for radial runout of the compressor rotor?

[@Jigme85]

Oh this is such good additional material to my purely academic studies! Thanks a lot! BTW... is that a CF-6 Fan blade in the background @ 1:48?

[@Squat5000]

On something like this, I could see there being immense axial loading, and with a properly balanced shaft, minimal radial. On any of the newer engines, do you see them using conical bearings? Or is ball still the way to go? And second question, does the race form a gothic arch profile (2 points of contact on the balls) or standard radius, with just one point? Awesome video as always, to say the least... Things we would never have a chance to see.

[@AgentJayZ]

+Cody Smallwood Spherical balls, circular race. Line contact.

[@Squat5000]

Thank you! I cant even begin to imagine the hardening and grinding process on precision bearings like that...

[@AgentJayZ]

Then it would not be a thrust bearing, would it?

[@jimbojones806]

So just to clarify, is it that big nut squashing/securing all the seals and inner races of the bearing together on the shaft is to reduce axial movement so that way the inner race is secured to handle the axial thrust load?? And that outer plate that's the outer race sits behind also resist the axial thrust as well?? I have worked with tilting thrust bearings where the inner race is actually designed into the shaft itself to secure movement that's why I ask the above question Are there any engines out there that use tilting pad bearings or is it all roller bearings??

[@AgentJayZ]

Yes, the two-part inner race of a large ball bearing is attached to the shaft. The outer race is mounted to the "frame" which is a major component of the engine outer structure. Being a deep groove ball bearing, it allows the shaft to turn, but not move in any other way.

[@ramprasadsharda556]

Ok 👍 sir here I got mine answers

[@stereosphere]

What does the engine use to transmit its thrust to the airframe then? In your diagram, I was thinking everything is spinning except part of the thrust bearing. Am I right? Thanks for a great series!

[@Pugjamin]

Jay, another amazing video! I dont know if you have ever heard of fred dibnah from the UK? but you remind me of a jet-age version of him! What i was wondering, when using the torque multiplier to torque the main nut to 'just over finger tight, 600ft-lbs, how do you stop the compressor rotating? i guess you dont just 'stick a bar down the blades!!' Thanks!

[@stevenlamphear1945]

Arrived late to this party...seems like 0 viscosity oil would leak right out of that...I'm fairly certain you discussed that already... Can you please point me to one of your previous videos? thanks, -Steve

[@AgentJayZ]

Jet Engine Lube System is where I discuss oil, I think.

[@Coughtry]

😢When he said GM I got excited and the only thing I could think of was a lsa turbojet.

[@nagarjunakolli]

while operating do the inner race and outer race vibrate seperately ? i am asking this because i don't know if any part holds both inner race and outer race together in a bearing.

[@petroldevo9934]

If you clamp the bearing to 600lbs, how does the turbine itself turn so free ?

[@AnonCh4r1i]

As a turbine n00b I'm surprised the main thrust bearing isnt lubricated, or made of some adamantium type ceramic,

[@AgentJayZ]

+Hydrocarbon Primate What do you mean not lubricated?

[@AnonCh4r1i]

It's ok I found Jet engine lube system, great videos! I'm subbed.

[@shaithesm0ck]

So why does it need seperate carbon (oil) seal and air seal? wouldt the air seal be even tighter to not let thru "thinner" air, and so be tight enough for the more viscose oil?

[@19cmurry85]

Awww it sounds sooo bad but the runout still looks so good! Do the engine mfgs. produce the bearings or do they buy from a dedicated bearing mfg.?

[@sandeepkhelna3488]

Amazing👍👍👍👌👌👌

[@haidarakbarsujana3744]

It's made from steel or ceramics???

[@AgentJayZ]

I made a video about just that subject... the lube system

[@free8704]

So is it the same setup for the rear of the engine also and the turbine is essentially clamp into the engine case from each side? It is surprisingly hard to find info on how the actual turbine shaft is connected to the rest of the engine

[@AgentJayZ]

If you want to see the insides of a jet engine, that's what my channel is all about.

[@stephensidaras7416]

Right but how do they work? Seems like they would melt or cause a bunch of drag. Thanks for the response!!

[@AgentJayZ]

+Stephen Sidaras How does what work? Need a time in the video, or a more detailed description.

[@davidhoekje7842]

Quite interesting. So the carbon seals isolate the oil supply from the areas outside of them, and the labyrinth seals presumably keep the compressed gasses or air following the required path. I've noticed you discussing the pressure of the compressed gasses being up to 300 psi in some engines. I'm curious what the pressure difference is between the lubricating oil and the compressed gasses in the area of this thrust bearing. It seems like the lubricating oil could be kept at a pressure similar to the air outside to reduce the force against the carbon seal. If it's similar to water pumps that use carbon seals, the area of higher pressure serves to hold the seal surfaces together. Do you know the approximate pressures offhand? Is the pressure of the lubricating oil varied to protect the seals?

[@AgentJayZ]

The oil does not protect or assist the seals in their function. Lube oil PSI is shown on the monitor of many of the engine test videos. It varies from 2 to 80 psi depending on a lot of things. the bearing sumps are not exposed to CDP, or gas path pressures, which can be as high as 600 psi in modern engines. The bearing sumps are close to atmospheric pressure under normal operation, as they are isolated from the gas path, in part by the carbon seals.

[@davidhoekje7842]

Thank you!

[@joevignolor4u949]

Hi Jay - How does the thrust bearing get lubricated during engine operation? Is it just greased at installation and the grease is retained and lasts the life of the engine? Or does the engine oiling system continuously supply oil to the bearing?

[@AgentJayZ]

The thrust bearing of an aviation or aeroderivative gas turbine engine benefits from one of the most highly engineered and sophisticated lubrication systems of all. Please see my video: Jet Engine Lube System, as well as the Main Bearing series, as well as mu other thrust bearing videos. Cheers.

[@jxavier9560]

How is the bearing lubricated? Are the other bearings on the rotor assembly too of similar construction?

[@AgentJayZ]

Have a look at my video called jet engine lube system. It tries to explain that.

[@coalhouse3171]

thanks

[@dayanandshirke7333]

🙏

[@michall8006]

Hi! You are balancing compressor rotor without thrust bearing components, seals etc. Is it a manufacturing requirement ? Thanks,

[@AgentJayZ]

Michal L The rotating inner races and roller elements of the bearings are assumed to be balanced, since they are built to dimensional tolerances of less than a thousandth of an inch overall.

[@michall8006]

AgentJayZ Sure those elements are well made. Do you check vibes level on engine during test cell run ? btw thanks for posting such valuable videos

[@ToyotaKTM]

Hi. How hot do you heat the parts to make them slide onto the shaft? How do you heat the parts?

[@user-kd8vc9ql7b]

excuse me,I have questions to ask, How to repair LM-2500 gas turbine B-SUMP? How to confirm 23699 oil leak out from B-SUMP?

[@AgentJayZ]

The overhaul manual contains all the procedures, troubleshooting, tools and parts required.

[@user-kd8vc9ql7b]

Thank you for your reply! I konw ,but I still can’t find the way to solve. So,would you help me? Would you have the related video to refer?

[@leeleslie6615]

is this a thrust bearing? i think it can only support radial force

[@AgentJayZ]

It's a deep groove ball bearing. Don't trust me; look up the capabilities with any bearing manufacturer.

[@sethjensen54]

When you put the bearing races etc on the shaft you heat them. When you remove them does it take heat or do you just pull?

[@AgentJayZ]

+Seth Jensen Brute force, applied with great care.

[@nhnifong]

What kind of failures would cause an engine to explode?

[@henry2008kim]

hello.. I've seen some rc model turbojets use 2 angular contact ball bearings butted against shaft casing and shoulders of centrifugal compressor and turbine wheel.. to take up clearance and provide an axial preload they use springs or compression washers.. because un preloaded the balls and the race might slip against each other instead of rolling and cause wear(supposedly). But I see no such spring or provisons for preload in your diagram and I've noticed full size turbines do indeed use split race type bearings as shown in your video.. my question is.. is there any need for preload in those bearings? and if there is how is it done? Thanks in advance! I always enjoy your videos... love them so much

[@AgentJayZ]

The ball bearings are called thrust bearings because they handle axial loads on the shaft. There is only one thrust bearing on each shaft. The compressor and turbine produce axial loads when they are operating, so there is no need for preload. I never consider the engineering or design of home made turbine engines... because there isn't any. All of the ones I've seen do so many things wrong or omit so many parts that they are dangerous. To compare them to professionally engineered turbine engines is a complete waste of time.

[@henry2008kim]

+AgentJayZ Agent.. If you were to design a turbojet that has a single centrifugal compressor stage and a single axial stage.. what kind of bearings would you use..? I humbly ask because frankly I'm not sure which direction the shaft would be loaded in running condition.. I would tend to think it would be loaded towards the rear.. but I don't know for sure

[@henry2008kim]

+Sangyoon Kim And if thats how its loaded then a lot of model turbine makers are doing it wrong as you mentioned.. they are trying to counteract natural preload direction by loading a spring against the force...

[@AgentJayZ]

The thrust bearing is a deep groove ball bearing. It can handle loads in either direction. Usually in a turbojet the force placed on the shaft by the turbine is greater than that by the compressor, so it is rearward. Have a look here, and you can win a small prize if you can identify the engine they based the diagram on. aeromodelbasic.blogspot.ca/2012/05/thrust-distribution-distribution-of.html

[@henry2008kim]

+AgentJayZ Thanks for the link! I'm reading it now... the engine is Rolls Royce Avon?

[@stephensidaras7416]

Love ur show. How do the air seals work?

[@ericdixon2898]

Air resistance. Air seals are simply to reduce compressed air from being leaked out and waisted.

[@AgentJayZ]

+Stephen Sidaras Look at the index in Your Questions Answered for Labyrinth Seal...

[@AgentJayZ]

Much debate on that one amongst the technical people. To get a full understanding, you may have to skip past the aeronautical engineers, and find yourself an aerodynamic scientist. Good luck with that.

[@baklazanivanovich7566]

how it works??? i dont understand!!!

[@Andyroid_]

How do you torque that nut to 600 lbs ft? Torque wrench with a cheater bar?

[@estebanwedontneednostinkin9969]

How does it get lubricated grease oil?

[@AgentJayZ]

Video: Jet engine lube system.

[@turtlemann14]

that's about a $800 bearing isn't it?

[@salmanaljaz4334]

All thrust bearing is ball bearing or some use other types ?

[@AgentJayZ]

With a name like that, I would expect you to be very precise with your words. There are indeed other types of thrust bearings. I once had a bicycle with a thrust bearing in the headset that had a radially arranged set of cylindrical rollers. Tapered roller bearings also are used in the steering heads of motorcycles, and in many other thrust applications.

[@salmanaljaz4334]

AgentJayZ thanks for clear answer , i read that the ball type use in high speed shaft such as jet engine but dont use in havey duty is that right ?

[@AgentJayZ]

I can only comment on the stuff I work on, and I have only seen ball bearings used as thrust bearings in aeroderivative gas turbine engines.

[@salmanaljaz4334]

AgentJayZ thanks

[@AgentJayZ]

Full Authority Digital Engine Control. It's like fuel injection for your car instead of a carburetor. There, that was easy, wasn't it ?

[@digranni128]

What is the name of the place where you work?

[@AgentJayZ]

+digranni Most of us call it "here". Geographical info is available throughout my video collection.

[@SgfGustafsson]

What company makes the bearings in the LM engines? Is there a fairly common maker for most of the ball bearings in the engines you work on?

[@AgentJayZ]

+Seigfried Gustafson The bearings used in an engine are made by a variety of vendors. So there is an engine manufacture part number that is standard for any give part. Then there is a bearing maker's part number, which will be different for each of the various sources of that bearing. Then there is the serial number, which is unique to each individual bearing.

[@SgfGustafsson]

Thanks for the reply!

[@AgentJayZ]

Yes that seal is a mirror image, isometrical, bisexual... it goes either way...

[@MatoRohacek]

Space age vans? wth? I thought you were repairing aircraft engines?