ARTICLE REF – ART149
You can see clearly in the diagram the location of the Exhaust Casing. First you need to remove the GG to a workshop and then start the replacement procedure.
Below on the left photo you can see the nine strut supports for the number six bearing. The struts are hollow with a cast support strut in each. The oil supply, scavenge, vent lines pass through these struts also. On the right photo you see extensive damage to one of these struts. Once the sheet metal protection has been compromised the hot gases will cause the cast struts to crack. Once they crack the exhaust casing is scrap. This is a very expensive part and that is why it is so important to inspect them when borescoping. This is the most common reason for exchanging this casing in the field.
Exhaust casing removal
The next part is already loose as the blots holding on the main cover also pass through this cover. It is used to guide the cooling air and as a heat transfer material. There is a cutout for the oil supply pipe so it can only go on in one position.
Remove the bolts from the bearing cover plate and it can be removed. There are thread inserts in these screw locations. Have some new thread inserts available as they are very difficult to re-install once they come out a bit.
If you are using the blue PWPS support tool to do the repair, you will have to support the turbine further back and allow the exhaust casing free to be removed.
The rigging of the exhaust casing worked out well as shown. The center of gravity is towards the front of the casing so the lifting strap was biased to tilt the casing aft. A chain block was then connected to the aft flange of the exhaust casing to control the tilting of the casing.
Tool PN TC 350-17 which is used to control the center of gravity when lifting the power turbine was attached with long bolts and spacers to the aft flange of the exhaust casing.
Four of these guides in the photo were manufactured (not a PWPS tool) to guide the casing rearward so it would not bind up on the seals. If the casing is not taken off squarely there is a chance that the labyrinth seals or the number 6 bearing seals would be damaged or cause the casing to hang-up.
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