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I have another question related to maintenance practices. During replacing MLG wheel of A320, it is said that we need to tighten the wheel nut 3 times with different torque values. The first one has the highest value. Then, we need to loosen and tighten the wheel nut again, however, with lower torque values. In my opinion, I think that the highest torque value is to put the wheel all the way on the axle, however, I was unable to find the answer for why we need to torque the nut again for 2 different values. And are there any other reasons for tightening the wheel nut with different value? Thanks for your answer.

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  • $\begingroup$ That is intriguing! My automotive maintenance experience is that sometimes you torque everything to a lower setting (ensuring the part is mounted evenly), then torque to the final, higher setting. Additionally, some bolts are "stretch bolts" that are one-time use - the incredibly high torque setting literally stretches the bolt and that is what holds it from coming lose. Tightening to a high setting then loosening and re-torquing to a lower setting is very counter intuitive! $\endgroup$ – FreeMan Oct 18 '19 at 19:10
  • $\begingroup$ I also have the same question. According to the AMM, we need to torque the wheel nut initially with the highest torque (for example 240lb.ft) . Then loosen it, tighten it again with second value (for example 70 lb.ft), and torque with final value (for example 110 lb.ft) $\endgroup$ – dingdingdong Oct 19 '19 at 12:49
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FreeMan - Commercial jet aircraft wheels are installed with a single nut on the axle, like a wheel hub on a car. The commercial jet aircraft axle is a few inches in diameter and is hollow. The wheel bearings are tapered, and while the axle nut is being tightened the wheel is spun ih the normal direction of rotation. A higher initial torque is applied to the nut, and the pressure on the bearings helps to get the races properly seated while the bearings are rolling over them. The nut is loosened, then the process is repeated using the torque specs specified in the manual. One of the airlines I worked for had a policy that required that the final time the nut was tightened, it would be turned by hand. After a while, they went back to following the manufacturer's recommendations. To recap, really tight to seat the bearings, looser for in service operation. I hope that helps.

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  • $\begingroup$ Welcome to Aviation.SE! $\endgroup$ – Bianfable Oct 27 '19 at 17:53

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