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Old 10-11-2017
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TownsendsFJR1300 TownsendsFJR1300 is offline
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Originally Posted by boscoe99 View Post
I got a thought on outboard motor drain plug threads.

You know how aluminum is. It likes to fatigue and fracture. Not a lot of fatigue strength in the stuff. I am guessing that over a number of tightening cycles (maybe to the point of "let's just snug it down a bit more to be sure it does not loosen") the threads simply fatigue to the point that one day they crack and then are prone to letting go.

On another (the wrong) forum the OP said he was using a torque wrench to tighten his plug and it just kept on turning. Apparently with little torque being applied. I have heard this before from Yamaha four stroke owners. That the oil pan threads stripped and they were barely tightening the drain plug.

As a test, some other fools and me set out to intentionally strip the threads on a brand new oil pan. It took a hellava lot of muscle. Much more than any of us fools would have imagined. Actually took a breaker bar to get the job done.

So do you think my fatigue theory holds any water?

The torque spec is too tight to start with. My bike (Yamaha) uses the EXACT SAME BOLT, slightly less aluminum thread and is spec'ed for 30 lbs ft...

The F150 is spec'ed for 20 lb ft.

I torque them the same as the oil filter, 12 lbs foot (or good and snug).. It simply needs to be tight enough to NOT loosen... It's not going anywhere...

**There have been many cases of bikes, from Yamaha, with the drain plug torqued down WAY BEYOND 30 lbs ft. That alone may stress the threads from the factory...


Last edited by TownsendsFJR1300; 10-11-2017 at 05:59 PM.
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