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Post by turbochris on Jul 25, 2021 11:48:58 GMT -5
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Post by Richard OConnell on Jul 25, 2021 23:33:28 GMT -5
About a week behind on posting the teardown and rebuild, but I'll try to capture as much as possible and keep it in chronological order. So the teardown started with harvesting the Wren MW54 from the pocket bike.  Work started with the disconnecting of fuel lines, EGT, Tach, and starter. A few bolts later and the gas producer and power turbine were ready to be removed from the bike.   With extraction complete, the motor was moved to our makeshift indoor workspace away from the summer heat  |
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Post by Richard OConnell on Jul 26, 2021 0:33:06 GMT -5
After moving the turbine to a more accommodating climate, we began disassembly of the MW54. Based on some issues we were seeing with the engine with temperature and performance, we had suspicions that we would find a few things: -Evidence of the turbine rubbing -Drag caused by worn bearings -Possible heat damage A few additional things we wanted to look into: -Condition of the combustor and injectors -Condition of the compressor -Any evidence of heat forward of the combustor -State of the turbine, NGV, and free turbine section -Wear on the gears aft of the free turbine. Disassembly began with separation of the free turbine housing from the gas producer. In 4 bolts the two sections could be separated. From there, the starter and FOD guard assembly was removed and the air jacket was slid off the engine.   The compressor was pristine and there was no evidence of abnormalities around the diffuser. Screws and accessories were carefully bagged and labeled to ensure everything goes back where it came from. The combustor had a single crack along one wall. Reorienting the motor revealed this crack ran along the very bottom. Possible evidence that fuel may have pooled and burned at some time?  A brief visual inspection of the turbine didnt reveal anything unusual. Tooling marks indicate the turbine has either been balanced many times or someone in the past may have struggled to get the balance correct. Either way, we wouldnt find out more until we got the compressor off.  |
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Post by Richard OConnell on Jul 26, 2021 0:54:51 GMT -5
(still catching up from last weekend) Next was getting the compressor off so we can free the rotating assembly and get into the combustor. This was a lot more difficult than it should have been and I unfortunately did not take more pictures of the process. So we started like any reasonable people by removing the compressor nut and attempting to tap the wheel out. It quickly became evident that this wasnt going to do it. we tried applying a bit of heat to the compressor while shielding the center shaft as best we could to allow it to slightly expand, hopefully freeing it, but still no dice. After a brief bout of defeat and with no real options left, we did a bit of research on the compressor and came up with an 'absolute max temperature' we would allow ourselves to reach heating the compressor wheel with a heat gun. During the process, the wheel was monitored with a FLIR camera and we took constant heat samples from all over the compressor. Since we were going through such length to free the shaft, we were also taking off the gloves. More force would need to be applied to the shaft to free the compressor. We settled on using a drill press to apply force to the shaft and push it through the heated compressor wheel. Thankfully, the wheel finally freed itself before we reached our 'safety temperature' and we could proceed with disassembly.  With the shaft out, we got our chance to look inside the combustor. There was a good bit of carbon buildup at the base of the combustor can and one of the vaporizer tubes was about a quarter inch shorter than it should have been.    With the turbine free, we were also able to take a look there. As suspected, there was evidence along the inner wall of the NGV and the outside of the turbine blades of rubbing.  |
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Post by Richard OConnell on Jul 26, 2021 1:19:01 GMT -5
Further inspecting the NGV gave us some insight into why the turbine was rubbing. It was warped, either as a manufacturing defect or something it developed over time. checking it with a multimeter revealed about .002 of warp. Chris made up a mandrel in the lathe out of stuff lying around the garage and took it down by about .004, which was still well within the clearance specifications for this motor.    I'll take a breather and follow up with another progress dump tomorrow. |
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Post by turbochris on Jul 26, 2021 19:28:29 GMT -5
I used the dynex balancing kit today. I have the optical rpm sensor and two of the mems accelerometers. Also- the stock wren rpm sensor plugs right in and seems to give a real clean signal.
I tried it out on the power turbine. There's a way to input loads of data and use trial weights that will help you figure an exact weight/radius/phase angle adjustment.
To hell with all that. I just used the rpm sensor and the mems near the turbine to measure the shake. I used test weights and tried to get the mems output as low as possible. Once i got the hang of it I figured out where the heavy spot was and had it balanced real close with a 35mg weight at around a 15mm radius.
If we moved the weight phase angle, the mems output got worse, if we moved the weight closer or further from the shaft CL, we could just about hide the imbalance in the bearing noise and if we went further the phase angle would shift roughly 180 degrees.
It's useable but you have to play with it.
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Post by Richard OConnell on Jul 27, 2021 0:10:06 GMT -5
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