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Old 10-11-2017
boscoe99 boscoe99 is offline
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Join Date: Jul 2013
Posts: 8,504

It might have taken over 150 pound feet of torque to intentionally strip the threads. It was a struggle even using a breaker bar. Even though most folks that don't use a torque wrench will over tighten fasteners, I can't see anyone ever coming anywhere close to mechanically breaking perfectly good threads on a Yamaha outboard motor drain pan.

Which is why my hypothesis is that over time, given sufficient tightening and un-tightening cycles, the aluminum threads crack and break. Those are cut threads I believe. Not rolled threads. Cut threads are more susceptible to cracking at the root of the thread. Everything is fine until one day it is not.

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