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Author Topic: APS/Ω Gas turbine bike build  (Read 575008 times)
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wobblywalrus
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« Reply #1800 on: December 12, 2018, 02:00:42 AM »

Aluminum expands more than steel when heated.  Sometimes if the steel shaft is too strong it will not stretch enough when the assembly gets hot and expands.  Plus, some aluminum alloys get softer when heated.  The aluminum cam be crushed under the nut at the end of the shaft and the fastener comes loose.

This was told to me last year when I was fixing the problem with the case bolts coming loose on the Triumph.  I was going to make some thick and strong case bolts.  The bolts need to stretch, I was instructed.   
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Interested Observer
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« Reply #1801 on: December 12, 2018, 09:39:00 AM »

Anders, regarding the O-ring...
For the edification of all us turbine-ignorant onlookers, could you perhaps elaborate on the oil circulation system?
From observing the recent photos, it looks to me that the curved pipe is the oil supply line to the thrust pads and the oil going past the pads is to be contained by the O-ring except for the gap in the O-ring which provides a narrow escape path for the oil.  Is that at all correct?  If so, where does the oil go after it passes through the gap and how is the suction pump acting on it?  Or, if oil is not intended to pass through the gap, why is there a gap in the first place?  How is the oil scavenged?
The sooty photo shows bits of O-ring material on the exterior of the tunnel.  If the scavenge system was sucking up the O-ring, why are there bits of it on the outside?  Looks like the thread of material has been there for a while, waving around in the wind.
The thrust pad photo shows a clear imprint of the O-ring channel on the “good” side of the oil port but on the other, damaged side, there is no comparable print of the channel and what looks like a contact patch on the ID where the ring could have been squashed.  Are the contact surfaces there sufficiently flat to eliminate an extrusion gap there?
I’m confused.
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charlie101
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« Reply #1802 on: December 12, 2018, 04:10:15 PM »

Careful, so you don't make a bigger problem.
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Mobacken Racing
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« Reply #1803 on: December 12, 2018, 05:27:51 PM »

Anders, regarding the O-ring...
For the edification of all us turbine-ignorant onlookers, could you perhaps elaborate on the oil circulation system?
From observing the recent photos, it looks to me that the curved pipe is the oil supply line to the thrust pads and the oil going past the pads is to be contained by the O-ring except for the gap in the O-ring which provides a narrow escape path for the oil.  Is that at all correct?  If so, where does the oil go after it passes through the gap and how is the suction pump acting on it?  Or, if oil is not intended to pass through the gap, why is there a gap in the first place?  How is the oil scavenged?
The sooty photo shows bits of O-ring material on the exterior of the tunnel.  If the scavenge system was sucking up the O-ring, why are there bits of it on the outside?  Looks like the thread of material has been there for a while, waving around in the wind.
The thrust pad photo shows a clear imprint of the O-ring channel on the “good” side of the oil port but on the other, damaged side, there is no comparable print of the channel and what looks like a contact patch on the ID where the ring could have been squashed.  Are the contact surfaces there sufficiently flat to eliminate an extrusion gap there?
I’m confused.


The oil enters through the curved pipe, then onward to each of the two journal bearings plus the axial bearing to which the small pipe with the silicone o-ring goes.



After passing through the small pipe it enters an oil gallery behind the thrust washer, a pad with 6 small holes where the oil exits and produce the film that takes up the axial load against the rotating thrust bearing. After being slung out of the thrust bearing the oil enters another bigger gallery where it drains back to the tank through a suction pump.

The damaged silicone rope is sealing that drain gallery, so there is no pressure at all there but an underpressure produced by the suction pump.

I hope I managed to explain this, in my head it makes perfect sense at least. Smiley

The reason for the gap was that by the time I milled the slot I hadn´t decided how to get the oil through the joint and into the thrust washer, so I had to leave some space there. After that I sort of forgot about it, never thought it would be a problem.

Anyway, that damaged seal is the least of all problems. I am not sure that it even is a problem, it sucks in a bit of air but other than that I don´t think it matters much.

Cheers!
/Anders
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Mobacken Racing
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« Reply #1804 on: December 31, 2018, 05:24:12 AM »

The last bits of work on JU-02 for this year, I got up early and spend a while in the workshop. First I centered the compressor cover around the wheel and drilled holes for 5mm dowels, earlier I used M5 screws but the diametrical fit was sloppy enough to allow the cover to misalign.



Then I welded the NGV´s properly, earlier I had just melted them in place without filler rod but now I added a bit more since I saw signs of a few hairline cracks in them. I will off course recheck the turbine clearance in case the welding has warped the NGV a little.



The suction line oil filter was also added, now I am filtering the oil both before and after the pump so I think the engine will be getting pretty clean oil from now on.



The loosening nut mystery is solved by the way, a friend made a test rig to measure how much torque needed to twist the compressor on the shaft and it was much higher than what the turbine can produce in running conditions. The only way the nut can come loose then is if the compressor has made contact with the housing, and this might have happened when the compressor cover was misaligned.

Cheers and happy new year guys!
/Anders

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