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turbine bearing types

Old 11-22-2021, 08:49 AM
  #51  
hendrix
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I really don't know, i will wait for the bearings from AMT to arrive in order to compare the two sets.
I am 100% sure that this is coming from the bearings under preload only.
UPDATE, Nop it does it again when the lubrication effect of WD40 fades away.
Chris

Last edited by hendrix; 11-22-2021 at 10:14 AM.
Old 11-22-2021, 08:51 AM
  #52  
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Originally Posted by JSF-TC View Post
Maybe some of the balls are not perfectly spherical and they find a high point?


Paul
On the friction in the rotation of the bearings is probably not placed correctly on its base, and is a bit off alignment. it needs proper alignment when mounting on its base.

Last edited by cptnassos; 11-22-2021 at 08:56 AM.
Old 11-22-2021, 09:26 AM
  #53  
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Originally Posted by cptnassos View Post
On the friction in the rotation of the bearings is probably not placed correctly on its base, and is a bit off alignment. it needs proper alignment when mounting on its base.
This friction is not constant, it manifest itself in a random fashion and only when the shaft is under full preload.
Usually the shaft spins very smoothly for ever but sometimes it just encounter friction.
I have cleaned everything to perfection and there is nothing to adjust so if this is the cause then the shaft tunnel is crooked.
From what i can feel when the shaft is under that friction if i turn it in the opposite direction i can sense a free region of about 5 degrees left and right exactly, it feels like the balls are causing this friction.
Chris

Last edited by hendrix; 11-22-2021 at 09:30 AM.
Old 11-22-2021, 10:05 AM
  #54  
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Ok i just disassembled the turbine again and gave it a thorough clean up.
Now everything works fine but i didn't torque the starter cone nut all the way.
Does anyone know how much torque i must use when tightening this nut?
Maybe i was over tightening this nut, i found somewhere that the tightening torque should be 1.2 Kg/m ((11.3nm-11.9nm)) maximum but i am sure that i used much more than that initially....
UPDATE
It needs more testing so i can be sure that everything works fine as it does it again but this time much less, maybe it needs some running in...
Chris

Last edited by hendrix; 11-22-2021 at 10:39 AM.
Old 11-22-2021, 12:06 PM
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From the test i did i concluded that the occasional friction is cause by the ceramic balls touching each other because where they touch they turn in opposite direction.
This also explains why the occasional friction is preload AND quality of lubrication dependent and why when the friction starts if i reverse the rotation the friction goes away.
Anyone having a different idea please step in, i am open to any suggestion.
Chris
Old 11-22-2021, 02:14 PM
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Originally Posted by hendrix View Post
From the test i did i concluded that the occasional friction is cause by the ceramic balls touching each other because where they touch they turn in opposite direction.
This also explains why the occasional friction is preload AND quality of lubrication dependent and why when the friction starts if i reverse the rotation the friction goes away.
Anyone having a different idea please step in, i am open to any suggestion.
Chris
A simple reminder about the ambient temperatures where you do the rotation tests. The bearings rotate at very high speeds and temperatures so there is a temperature tolerance for the balls, try preheating the turbine in an oven at a temperature of about 140Fdegrees and try again. this is probably because the bearings are new and cold and need to work for a while.

Last edited by cptnassos; 11-22-2021 at 02:27 PM.
Old 11-22-2021, 08:38 PM
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THANK YOU very much for the information, i will do it.
Chris
Old 11-22-2021, 11:03 PM
  #58  
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Originally Posted by hendrix View Post
From the test i did i concluded that the occasional friction is cause by the ceramic balls touching each other because where they touch they turn in opposite direction.
This also explains why the occasional friction is preload AND quality of lubrication dependent and why when the friction starts if i reverse the rotation the friction goes away.
Anyone having a different idea please step in, i am open to any suggestion.
Chris
Yes this is correct, and is one of the downsides of using full compliment bearings. It get a lot worse after an engine run where the engine is not cooled down. It can then lock up quite solidly, to the point where the starter will not turn.
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hendrix (11-23-2021)
Old 11-23-2021, 12:43 AM
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Ahhh that explains it nicely, i also did the following test, i measured the spin down time while the turbine is oriented in different axes with wd40 lubrication only and spinning it by hand.
I took one measurement with the compressor looking up, then another with the compressor looking down and another with the turbine level and i found that when the compressor is facing down the spin time is definitely shorter, there a bit more friction.
My only explanation is that the weight of the shaft assembly adds to the preload because nothing is loose or missing.
I can't wait to test the AMT bearings (GMN actually) with he brass cage, from what i have learnt so far they should work very well...
Chris

Last edited by hendrix; 11-23-2021 at 12:50 AM.
Old 11-23-2021, 03:17 AM
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A simple reminder about the ambient temperatures where you do the rotation tests. The bearings rotate at very high speeds and temperatures so there is a temperature tolerance for the balls, try preheating the turbine in an oven at a temperature of about 140Fdegrees and try again. this is probably because the bearings are new and cold and need to work for a while.
I performed the test but i found no change.
The bearings probably need some running in, this weekend i will fire the turbine up and test it.
Chris
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cptnassos (11-23-2021)
Old 11-23-2021, 06:14 AM
  #61  
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First test run and everything is fine, the bearings do make a strange and louder sound but i guess this is normal because the turbine is installed inside the airplane (a old but airworthy Boomerang intro without any scratch) but everything spins without any friction.
i will repeat the test run tomorrow as i don't have any more free time left for today.
Chris
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cptnassos (11-23-2021)
Old 11-24-2021, 08:54 AM
  #62  
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I just received the GMN bearings from AMT. they look and feel serious..
Today i did another run on the Ebay bearings, they are excellent, no friction, no noise they run silky smooth.
I don't know if i will fit the GMN caged bearings any time soon as i will have to burn a lot of fuel with the ones i just installed i think...
Chris
Old 11-24-2021, 10:20 AM
  #63  
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Originally Posted by hendrix View Post
I just received the GMN bearings from AMT. they look and feel serious..
Today i did another run on the Ebay bearings, they are excellent, no friction, no noise they run silky smooth.
I don't know if i will fit the GMN caged bearings any time soon as i will have to burn a lot of fuel with the ones i just installed i think...
Chris
Perfect good job.
Old 11-24-2021, 11:03 PM
  #64  
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Originally Posted by hendrix View Post
I just received the GMN bearings from AMT. they look and feel serious..
Today i did another run on the Ebay bearings, they are excellent, no friction, no noise they run silky smooth.
I don't know if i will fit the GMN caged bearings any time soon as i will have to burn a lot of fuel with the ones i just installed i think...
Chris
Some 23 years ago I tested Brass caged GMN bearings provided as a sample. Those had the white ceramic (Alu oxide) balls. At the time balancing was an issue for me and they broke at about 150KRPM. Balls physically broke up. SiN balls are much harder and robust.
Also they were deep grove I think.
Old 11-25-2021, 06:50 AM
  #65  
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No those are angular contact and have silicon nitride balls, specs here s608cta.pdf
In fact i will fit them on Monday i hope and see how they perform.
I tried to fit one on the compressor side but it won't fit in the shaft tunnel and it is getting stuck rendering preload useless.
I will try to enlarge a bit the shaft tunnel a i plan to replace it with an iron one.
UPDATE:
I used the dremel tool and some polishing compound and now i can se my self inside the shaft tunnel, that shine removed just enough material to make the GMN bearings slide nicely in.
The GMN bearings had 2 hundred of a mm larger outer diameter (22,00 mm instead of 21,98 of the GRW bearings.
Chris

Last edited by hendrix; 11-25-2021 at 11:44 AM.

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