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Post by racket on Apr 11, 2015 18:09:32 GMT -5
Hi Mark
Heh heh , yep , nice to see shiny machined alloy :-)
Cheers
John
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Post by madpatty on Apr 11, 2015 22:46:19 GMT -5
Hi Racket,
I am just curious to ask that while designing a shroud for an engine that uses bushes rather than ball bearings...doesn't the compressor blades touch the shroud when moved Radially with hand with such tighter clearances.??
I face this problem whenever i design compressor shroud...i always reprofile and refit the part again and again...but my method of checking is moving the shaft radially in all directions with hand till the point when not a single part of any blade from inducer to exducer is touching the shroud anymore....but this way i think i am always getting more than required clearances because brass bushes already have some amount of radial play in them even when there is an oil film between them.
Cheers,
Patty
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Post by racket on Apr 11, 2015 23:35:54 GMT -5
Hi Patty
At the inducer the radial clearance between inducer tip and shroud isn't all that critical , for your wheel I'd be using ~0.010" -0.25 mm radial clearance( 0.020 -0.5mm diametrical)
But at the exducer its a different matter as you want minimal clearance to prevent air escaping through the clearance , so probably 0.005" - 0.125mm axial , with the rotor pushed forward to take up the axial thrust bearing clearances .
We don't want too much clearance because it effects efficiency , but we also don't want too little resulting in the wheel contacting the housing .
Are you using "new" bearings with "in tolerance" clearances between journal and bearing ID and between bearing OD and shaft tunnel bore ??
If you are using used bearings with unknown clearances then you may have to make sure you have plenty of oil pressure going to the bearings to keep the shaft "centralised" so that you can run "design" wheel clearances , even though the wheel could contact the housing if forced from side to side during assembly without that oil flow.
As an example , the Garrett GT6041 with brass bushes has 0.015" radial clearance ( 0.030" diametrical) between its ~106mm inducer and its shroud , 0.030 radially on the turbine exducer .
Cheers
John
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Post by madpatty on Apr 11, 2015 23:49:39 GMT -5
Hi Racket,
The brass bushes are not new ones but shaft is a new one without any rubbing at the journals....and i have oil pressure in the vicinity of 60 Psi...when pressurised the shaft is hard to move radially and that too a little radial movement.
I Didn got it checked but i think the shaft radial movement is just within limits as i have used same setup in standard housings before and this piece has got less play than many of my earlier setups.
But when without oil pressure they touch the shroud even at 1 mm diametric clearance or even 1.5mm but i am pushing the shaft with a much greater force radially which I don't think will be the case when the shaft will be rotating....
Does the blades in your setup touch the shroud when without oil pressure,?
Cheers,
Patty
Cheers,
Patty
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Post by racket on Apr 12, 2015 0:17:43 GMT -5
Hi Patty
1mm diametric is way too much for such a small compressor wheel , 1.5mm is simply an indication that your bearings are completely worn out and need replacing .
The Garrett GT6041 clearances I mentioned in my last email were on a remanufactured "new" turbo that had never been run , it has >twice the physical sizes of your wheel and its bearing clearances would be greater as well .
To be quite honest , I never checked if the comp wheel could touch the inducer shroud on the 10/98 engine by forcing the wheel from side to side , though there were very light rubs evident when the rotor was spun by hand after shutdown , nil oil pressure, but that could have been from asymmetric expansion/contraction between top and bottom of a cooling engine.
Cheers
John
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Post by madpatty on Apr 12, 2015 0:28:35 GMT -5
Hi Racket,
You never checked!!...that was a bit of shock for me as i was adopting this technique everytime i reprofiled the shroud from inducer to exducer......
I was using as much force as i can with a finger or two to push the rotor radially outwards to check if it rotor is touching the shroud...
But now i think even a standard NEW rotor will touch the shroud with the amount of force i was using to move the rotor radially outwards...
I saw a youtube video sometime ago regarding how to check a Used turbocharger, in which they used this technique of pushing the rotor radially.....but now i think it is not fully correct as i depends upon the oil pressure and also on how hardly you are pushing it ....
I think the best method is TAPE covering the blades for required clearance and reprofile the shroud and then leave the rotor and shroud as it is for the test run....if there is minor contact it can be let go otherwise remove some more material...
What do you think?
Cheers,
Patty
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Post by racket on Apr 12, 2015 2:51:33 GMT -5
Hi Patty
Yep , pushing the comp nut from side to side to see if theres contact between wheel and shroud is a good way of checking for badly worn bearings , but we're making gas turbines not turbochargers that need to run under less than ideal conditions, so we can "refine" the procedure somewhat by reducing clearances and making sure the wheel is centred in its shroud , check with oil pressure to see how it spins with a finger flick .
With a good supply pressure, the oil flow should "centre" the shaft and bearings once spooled up .
Cheers
John
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Post by racket on Apr 12, 2015 23:15:06 GMT -5
Hi Guys Holes drilled and threads tapped ( 8mm) for comp front cover fasteners, and 4mm for bellmouth flange  Bellmouth flange  Bellmouth mounted up on comp front cover snout    Just need to purchased some appropriate stainless fasteners to hold things together Cheers John |
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Post by smithy1 on Apr 13, 2015 4:02:30 GMT -5
Hi Patty 1mm diametric is way too much for such a small compressor wheel , 1.5mm is simply an indication that your bearings are completely worn out and need replacing . The Garrett GT6041 clearances I mentioned in my last email were on a remanufactured "new" turbo that had never been run , it has >twice the physical sizes of your wheel and its bearing clearances would be greater as well . To be quite honest , I never checked if the comp wheel could touch the inducer shroud on the 10/98 engine by forcing the wheel from side to side , though there were very light rubs evident when the rotor was spun by hand after shutdown , nil oil pressure, but that could have been from asymmetric expansion/contraction between top and bottom of a cooling engine. Cheers John Yep John....the 6041 is still good as new, with zero oil pressure the inducer is close to the inlet housing but not quite touching, there's a small amount of radial play as would be expected.....but when the oil pressure is ~65psi, she's rock solid and spins freely thanks to that nice thrust bearing setup..! Smooth as a baby's bum..! Cheers, Smithy. |
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Post by pitciblackscotland on Apr 13, 2015 4:21:46 GMT -5
Hi Guys Holes drilled and threads tapped ( 8mm) for comp front cover fasteners, and 4mm for bellmouth flange Bellmouth flange Bellmouth mounted up on comp front cover snout Just need to purchased some appropriate stainless fasteners to hold things together Cheers John Hi John, Bloody hell you don't stuff around very nice work  Cheers, Mark. |
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Post by racket on Apr 13, 2015 16:38:40 GMT -5
Hi Smithy
You must be getting those bearings "run in " by now :-)
Hows the A/B fueling coming along ??
Cheers
John
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Post by racket on Apr 13, 2015 16:43:28 GMT -5
Hi Mark
Yep , been putting in a few hours at the workbench , might get an hour or two more today , gotta workout axial positioning of the comp wheel for machining the rear of the diffuser wall where the thrust bearing is fitted ............its a fiddly job considering I only have a few thou to play with between too much or too little comp shroud clearance ...............thankfully I've got the 10/98 engines build journal to consult :-)
Cheers
John
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Post by smithy1 on Apr 13, 2015 20:43:51 GMT -5
Hi Smithy You must be getting those bearings "run in " by now :-) Hows the A/B fueling coming along ?? Cheers John Yep...she's certainly run-in....all the new gubbins are installed, new oil cooler, oil temp gauge etc, have a very minor oil leak at one of the hose joints though, pain in the ar$e.......just need to find the time and place to make some noise... Love your work btw....excellent as usual. I must make time to get up to see you mate...has been too long between cups of tea.  Cheers, Smithy. |
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Post by racket on Apr 13, 2015 21:38:05 GMT -5
Hi Smithy
You're welcome any time , the weather is finally turning cooler and the "north coast humidity" has gone :-)
Yep , you need to be burning fuel and making that A/B scream.
The new motor is starting to make sense , I've had to refit the front cover to the lathe so as to remachine the shroud profile a bit "deeper" to get the comp in the right axial position for the diffuser channel heights, having the extended tip on the comp wheel has been a bother as its difficult to measure exactly where things come to , so I'll keep "burying" the comp a half millimetre at a time into the shroud until things look "just right" .
Cheers
John
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Post by finiteparts on Apr 14, 2015 22:34:10 GMT -5
Nice looking parts your making there! Did you machine that bellmouth from a solid chunk or was it a casting too?
Thanks for sharing the pictures!
~ Chris
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