Why is this left hand thread? -- Fender

[RocketyMan]

Can someone please explain to me why this one fastener on the right side fender is left hand thread only when all the others are right hand thread--even on the left side fender? I didn't understand this until I looked at realoem and verified it is indeed left hand thread. Then I had to find the ONE bolt...nearly cross threaded this thing...

This is wild...
There must be a reason.
Is this just the engineers messing with us?



#14
https://www.realoem.com/bmw/enUS/sho...diagId=41_1706

Read the special note.

[NiBe]

I want to know that too!

[RocketyMan]

Originally Posted by NiBe

I want to know that too!

I can't be the only one, right?

Maybe there's an answer hidden in TIS...

[RocketyMan]

This is the best I got...

[amrazM]

i broke that fixing point the first time i took off my fender. dumb for sure.

[M3SQRD]

I don’t see a clear reason why a left-hand threaded bolt is used in a location that’s hard mounted. Typically, left & right threads are used when you want to increase or decrease the length of a rod with monoballs at each end (e.g., anti-sway bar drop link, camber arms, etc.).

[NiBe]

Maybe it is an Easter egg from BMW engineers.

[Theodore]

It wouldn't surprise me if it makes it easier on the factory line for a robot (or maybe a final inspection human?) to more easily keep the fender tucked closer to the unibody structure near that corner whereas tightening away from the unibody structure might tend to "move" the fender away from the hood a little widening the panel gap beyond allowable specification. At least that's why I would have chosen a reverse thread screw at that location.

[amg6975]

Originally Posted by Theodore

It wouldn't surprise me if it makes it easier on the factory line for a robot (or maybe a final inspection human?) to more easily keep the fender tucked closer to the unibody structure near that corner whereas tightening away from the unibody structure might tend to pull the fender away from the hood a little widening the panel gap beyond allowable specification. At least that's why I would have chosen a reverse thread screw at that location.

That was my though. Something about tolerances and how the panel moves when those screws are torqued.

[M3SQRD]

There is absolutely no difference in how a left-hand threaded fastener applies/develops preload. Only difference is you drive the screw in turning CCW, instead of CW. Nothing is getting “pulled” because it’s a thru hole.

[amg6975]

So there's no friction between the bolt head and panel?

[RocketyMan]

Originally Posted by amg6975

So there's no friction between the bolt head and panel?

The captured nut is in a plastic clip that is riveted to the plastic fender. So I have a hard time thinking the torque of the bolt (with capture washer) will apply torque to the fender.

Still doesn't make sense.

[M3SQRD]

Originally Posted by RocketyMan

The captured nut is in a plastic clip that is riveted to the plastic fender. So I have a hard time thinking the torque of the bolt (with capture washer) will apply torque to the fender.

Still doesn't make sense.

I agree 100%. Chalk it up to odd BMW design engineering to puzzle inquisitive BMW owners

In the design of spacecraft and payloads, left-right hand threads are used to dial in pointing requirements of antennas, optics, cameras, star trackers, etc. I can’t think of any left-hand threaded fasteners being used for any other purpose in 30+ years of designing one-of-a-kind spacecraft/space vehicle structures.