Reinstalling OEM Under Panel

[CRYPTiC]

My car never had an underpanel since I've owned it, so I finally plunked down the money to order one. Following what I read on Pelican Parts, realoem and a write-up I found on the BMWCCA of Pugent Sound, I bought these part numbers:

51-71-2-250-643 (swiped from this post)


17-11-2-227-690 (swiped from Pelican Parts)


It's pretty obvious where the big piece goes. But where the heck does the small one go?

[Balthazarr]

Never had that either.
I suspect the rectangular piece goes directly under the radiator above the
larger piece.

[CRYPTiC]

Hmmm ... do you think that little weird-looking cut-out could be for the radiator drain plug?

[Balthazarr]

Hmmm ... do you think that little weird-looking cut-out could be for the radiator drain plug?

You mean in the top piece?
Could be. The drain is on the driver's side.

I found some parts diagrams on realoem.com. You might want to look there if you don't have your own ETK.
Tough to id what they show with what you have.

[CRYPTiC]

Well, I did find this one after searching by part number:

http://realoem.com/bmw/showparts.do?...17&fg=05&hl=80

Seems to agree with my hypothesis, but the drawing doesn't show a cutout. Also, realoem and the ETK has been wrong before.

[Darron]

Hey Cryptic,

There are slots on each side of the larger (lower) peice that the smaller peice slides into. Then you install the entire assy. When mounted into the larger pecie, the smaller peice has a rubber lip that's flush with the bottom of the radiator when the installed.

[CRYPTiC]

Alright! I just figured out how to slot the smaller piece (vertically) into the larger under panel. There's a lip on the under panel that the smaller piece needs to catch onto when you assemble the two.

Now I just need to figure out a way to mount this onto the car without it falling out on me ...

EDIT: In the pciture below, the small piece slots into the parts marked in green. They catch onto the lip marked in red.

[camiloteram]

shouldnt you have felt a difference in the downforce your car has at highspeeds? I lost that same piece about 5 months ago, and the car blows on the highway now. It wants to take off.


The weird coincidence is that I just came upstairs from trying to install that same piece on my car and I couldn't figure it out either. I fear there is something else missing.

[pas]

An unsolicited suggestion: if you really want to use these stock pieces and hope to keep them on your car for a while, it would be well worth your while to try to do a few things to make them more robust. My suggestions:
1) at the various mounting points, reinforce the region around the plastic pieces by smearing a moderately thin layer of something like JB Weld or another epoxy - this will help distribute loads in conjunction with (2) below and hopefully will stave off the occurrence of having the bolts rip out
2) try to use larger washers to further distribute the loads
3) if you can, you might want to add some extra reinforced holes and simply tie-wrap the pieces to convenient support structure to provide extra protection from the underpanel pulling off at an inconvenient time.

Why all this do you ask - having wiped out on the track in part because my underpanel came loose and literally got under one of my wheels (literally the "last track event before I do all the reinforcing" I designed) it is worth considering.

For the peace of mind, I just use the aftermarket Al underpanel.

good luck.

[CRYPTiC]

shouldnt you have felt a difference in the downforce your car has at highspeeds? I lost that same piece about 5 months ago, and the car blows on the highway now. It wants to take off.

My car never had an under panel, so I hope adding one will make it feel like a new machine.

An unsolicited suggestion: if you really want to use these stock pieces and hope to keep them on your car for a while, it would be well worth your while to try to do a few things to make them more robust. My suggestions:
1) at the various mounting points, reinforce the region around the plastic pieces by smearing a moderately thin layer of something like JB Weld or another epoxy - this will help distribute loads in conjunction with (2) below and hopefully will stave off the occurrence of having the bolts rip out
2) try to use larger washers to further distribute the loads
3) if you can, you might want to add some extra reinforced holes and simply tie-wrap the pieces to convenient support structure to provide extra protection from the underpanel pulling off at an inconvenient time.

Good ideas.

I was thinking about this earlier and I might simply cut a 1" wide strip of sheet metal and use it to back any mounting screws I use. Think of it as a really big body nut. I'll either use really wide washers or another strip of sheet metal, and some lock nuts to hold everything together. Or something. I'd like to avoid using metal on parts that might fall off because I hate it when I puncture tires on the road.

[RRSperry]

All that smearing is a little much...lol I used a small flat 3/32 Al bar stock. I drilled a hole and used it as a larger washer. Fine for 12 years now... ;-)

[CRYPTiC]

Got this installed yesterday. The inner piece goes in as described above, with the cut-out on the left. The rounded edge of the under panel sits above the bumper cover. The task wasn't hard, but kind of annoying because I couldn't get the "pork chops" off the car and the fender lining was in the way.

In case anyone else reads this thread later: you'll need a bunch of sheet metal screws to reinstall the panel. I don't know the specs, but the hex head screws on the "pork chop" seem to fit. If you're missing any of the white "body nuts" then you're SOL; they're absolutely required to mount the panel. I was missing one, so I had to rig something up with spare parts.

I took it for a short drive afterwards and initial perceptions are that the car is a bit more stable and quieter (probably because the air is going under the car rather than into the engine bay). I won't discount the possibility of placebo, though, since the most recent drive before that was through heavy rain on worn tires.