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Old 12-17-2016, 03:31 PM
oldskewel oldskewel is offline
Join Date: Nov 2014
Location: SF Bay Area
Posts: 852
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Originally Posted by CapeX5 View Post
I have re used mine. And I think I have read most of the threads regarding this issue. In none I have read have I seen an explanation of what kind of engineered task that plate provides that necessitates the use of a TTY one time bolt! I don't want to start a whole pissing match on this, but would be very curious as to why. While I was working on my 01 I ran quite a while with the plate off and didnt' notice anything going on. Inquiring minds want to know....
Agreed. There are a few reasons they might have done it, but I have never seen a reliable explanation of the true reason(s). It is not as simple as that they needed it really tight and the bolt could not take it more than one time. No. If they needed it really tight, they could have used a bigger bolt that would not plastically deform, and could be reused without worry.

A smaller bolt, like this, has more compliance than a bigger bolt would have. Maybe they needed that. Head bolts are often TTY for this reason.

A 10.9 bolt that is already torqued past its yield stress is, by design, close to breaking. Maybe there is an intention for it to break away on a collision, as part of the crash design.

Making your customers pay $100 for bolts each time the pan is removed may make financial sense. And it may dissuade some DIY mechanics from getting into the car more than they maybe should.

Using M10 bolts may have saved them a couple of dollars over M12 bolts when initially built. And maybe they had a mandate to not spend a penny on lifetime beyond 100k miles.

So while I re-use mine, and think I know enough to let me do it safely, I'd feel much better if I knew the true reason they did it. I doubt we'll ever know for sure.
2001 X5 3.0i, 180k miles, AT, owned since 11/2014
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