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      04-05-2011, 09:50 PM   #1
LiM3y
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DIY: Under-tray skid plates

This is my first DIY, so bear with me...and any experts in metal working and technical writing better look away now!

I had to replace the whole of the front under-tray due to one thing and another. The middle section was cracked by a speed bump and the side sections have become worn through catching the road on inclines. I have Eibach springs with winter tires combined with a residential road resurface which exacerbated this and the driver side side section wore completely through at the corner. I had to replace all three sections, and I elected to generate home-made aluminium skid plates for the side sections. This is my story. The names are fictitious to protect the innocent.

Photo #1: The 12" x 18" aluminium sheet purchased from Lowes. I elected to use this grade to minimize weight and also be easy to work/cut with without special tools

Photo #2: Using the plastic/felt section I made an outline on the sheet, using the steel washer backers (see later) as a guide for distance. I aligned the piece a little away from the edge as I wasn't sure how the sides would line up when folded up. This also allowed the end to fold around to help get a good fit. I also cut tabs on the inside to fold over when attaching. Make sure you leave gap for the attachment screw to the middle section. The fitting with the centre tray is loose enough to allow the tabs to fit.

Photo #3: Using snips to cut out the shape. You can use the cut out shape as a template for the opposite side, you just flip the sheet over to get a mirror image. (This occurred to me after I repeated the templating process - Duh!)

Photo #4: The completed cut outs. I finished the sections after the photo to remove burrs and edges with a file and a Dremel. The cuts aren't great, but as my girlfriend acutely pointed out, what does it matter, no one can see them anyway! You can see my attempts at making sure the measurements were accurate on the metal!

Photo #5: The folded rear edge and the front section. I made small v-cuts in the front section to allow the metal to fold up without too much warping. The sections were bent upright a little bit (20-30 degrees) at a time with pliers gripping the marked line to create a fairly consistent fold.

Photo #6: The completed folded part mounted on the plastic/felt section. I have drilled 5 mm holes for rivets in the metal piece only. I drilled around the front and made a single hole on the underside near the outside edge. On the right side, you can see how I have folded the section at this acute angle. This small edge helps later with getting a good fit. You can see that I made slightly too wide v-cuts for the fit. [NB Be wary of the placement of the hole on the left (nearest the centre tray) as when the section is riveted, the rivet can interfere with the join with the centre section. Next time, I would place further to the right based on this view]

Photo #7:The sections prepped for painting. These were rubbed down with coarse sand paper and wiped down with Goo-Gone to degrease. I painted with a matte black engine enamel. I did have an attempt with rubberized chassis paint, but this did not stick at all on the aluminium (learning point!). I used several light coats

Photo #8: The painted parts.

Photo #9: The mounted skid-plates. I kind of went over board with rivets, but I didn't want them coming off at the wrong time! I backed all the rivets with a broad 5mm steel washer for extra support rather than rely on the plastic of the section as an anchor. I started by drilling the bottom hole first and riveting. I then folded the tabs, drilled through and riveted. The front and rear sections were riveted. I felt doing it this way afforded a much better fit of the skid plate on the felt section. I repainted the section to cover the rivet heads

Photo #10: The rivets I used and 5mm steel washer backers. These rivets were just the right length

Photo #11: This shows where I had to cut out the centre tray to accommodate the rivets on the tabs and the inside front section. This needs better judgment next time around.

Photo #12: The skid plates finally mounted.

Comments on mounting the under-trays. It is all pretty obvious when you are under there what needs to be unscrewed (8mm bolts around the front and wheel wells, 10mm (I think) where the front under tray meets the engine under-tray.

I mounted the middle section first. Do the Bowden A hangers first, and then the rear most screws by the engine undertray. When attaching the side sections, attach by the screw on the underside of the middle section and side section, some of the others attach to the wheel arch or bumper, so need to be lined up, then fix the screws furthest inside the wheel arch and work out. The screws need to reach through the wheel lining, the side section and into the fixed nut on the center tray. This needs a bit of tugging and is almost impossible when the outside screws are fixed (ask me how i know) but they will eventually fit. Work your way around making sure that all the sections (side, middle and underside of bumper) are buckled together.

There you go! Oh, and you will definitely know when they are working - the hollow under-tray amplifies the grinding of metal noise very well. It helps you learn where you habitually catch the undertray in your daily drive
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      04-05-2011, 10:13 PM   #2
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Did you know you can buy them for less than $20 each? And did you also know those pieces sacrifice themselves rather than the bumper when you hit something?
Anyway, not a bad job, but I expect to see that on 10-yr-old Civics, not an M3, but to each his own. Take care.
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      04-05-2011, 10:58 PM   #3
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Quote:
Originally Posted by elp_jc View Post
Did you know you can buy them for less than $20 each? And did you also know those pieces sacrifice themselves rather than the bumper when you hit something?
Anyway, not a bad job, but I expect to see that on 10-yr-old Civics, not an M3, but to each his own. Take care.
That's the point! This isn't cosmetic, it is to protect the underside of the car. You can't actually see them.

I couldn't find any E90 M skid plates when searching. The closest I came were Z4M skid plates from RPI for $60

Thanks for dropping by. Take care.
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      04-06-2011, 08:11 AM   #4
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Very cool DIY
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      04-06-2011, 09:59 AM   #5
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Nicely done!
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      04-06-2011, 10:00 AM   #6
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Quote:
Originally Posted by elp_jc View Post
Did you know you can buy them for less than $20 each? And did you also know those pieces sacrifice themselves rather than the bumper when you hit something?
Anyway, not a bad job, but I expect to see that on 10-yr-old Civics, not an M3, but to each his own. Take care.
WTF man? Have another shot of Geritol and take a nap
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      04-06-2011, 10:04 AM   #7
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DAMN bro thats nice... I can see why you did this... you need a little waxing on your bumper.
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      04-06-2011, 10:09 AM   #8
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very nice
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      04-06-2011, 10:17 AM   #9
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Quote:
Originally Posted by Sean05 View Post
DAMN bro thats nice... I can see why you did this... you need a little waxing on your bumper.
No kidding! Spring cleaning next weekend!

Thanks
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      04-06-2011, 01:15 PM   #10
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Quote:
Originally Posted by elp_jc View Post
Did you know you can buy them for less than $20 each? And did you also know those pieces sacrifice themselves rather than the bumper when you hit something?
Anyway, not a bad job, but I expect to see that on 10-yr-old Civics, not an M3, but to each his own. Take care.
Please tell us where. RealOEM lists those pieces at $36 and dealer markups would probably put it at near $50.
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      04-06-2011, 02:57 PM   #11
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Nice write up! As long as they aren't as loud as your track pads were you should be all set.

Let us know how they hold up.

PS: I would also be interested in where you can get them for twenty bucks and what the part numbers are.
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      04-06-2011, 03:20 PM   #12
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The only realOEM things I could find are the parts that I used, which are felt covered plastic insulation units, which cost about $36/each. These aluminium covers are designed to cover them. I cannot find bespoke metal/plastic skid plates for an E90 M3. That is why I built these in the first place, as I believe I am doomed to destroy more with the lowered car and the angle of my driveway relative to the road. I also wanted to make sure that the leading edge had some cover, as this was where the original parts abraded, rather than cover just the bottom of the section.

For a couple extra hours work, and I had to replace the parts anyway, it was worthwhile. (I think)
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      04-06-2011, 08:14 PM   #13
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Somebody else mentioned they got the OEM pieces for twenty dollars each. I have tried to look up the part numbers on realoem but have not had luck finding them. What are the part numbers for the pieces you replaced and then covered with aluminium? My passenger side under-tray has a nice hole in it.
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      04-06-2011, 10:59 PM   #14
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Quote:
Originally Posted by JohnnyRoaster View Post
Somebody else mentioned they got the OEM pieces for twenty dollars each. I have tried to look up the part numbers on realoem but have not had luck finding them. What are the part numbers for the pieces you replaced and then covered with aluminium? My passenger side under-tray has a nice hole in it.
http://www.m3post.com/forums/showthread.php?t=501712

It is part 23 in the diagrams. The switch is pretty straightforward, just reconnect the screws deepest in the wheel well first as these connect three section together (wheel lining, side section and middle section) and were tough to line up. I needed some extra screws (Part 8 in picture) as I lost some along the way.
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      04-07-2011, 12:49 AM   #15
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Quote:
Originally Posted by LiM3y View Post
That's the point! This isn't cosmetic, it is to protect the underside of the car.
When you hit something again and rip your bumper, you'll remember my post . Those pieces give the bumper rigidity, but if you hit them, you want to break them rather than the bumper; they're MUCH cheaper. That's what I tried to tell you man, but whatever. And yes, they look like crap too; it's the truth, and you know it. You should just buy stock ones and drive more carefully . Signing off. Take care.
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      04-07-2011, 08:09 AM   #16
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I think you are grossly over-estimating your role in my life. Take care.

Last edited by LiM3y; 04-07-2011 at 09:24 AM.
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      04-20-2011, 01:12 AM   #17
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despite elp_jc's disapproval, i think its a good idea. although i am too lazy to do this myself but i commend you for posting a DIY, i am sure this will give some ideas to other members who arent as lazy as me.
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      04-20-2011, 09:49 AM   #18
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would be cool if we could get a mold from the OEM piece and just make the same exact shape out of the aluminium like he did
so that way it would come out in one piece without all the cuts
and just paint it black and replace the OEM piece
it looks easy enough to be a DIY

heck you could also make a cut in it to vent air to the brakes


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      03-22-2012, 06:11 PM   #19
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Quote:
Originally Posted by elp_jc View Post
When you hit something again and rip your bumper, you'll remember my post . Those pieces give the bumper rigidity, but if you hit them, you want to break them rather than the bumper; they're MUCH cheaper. That's what I tried to tell you man, but whatever. And yes, they look like crap too; it's the truth, and you know it. You should just buy stock ones and drive more carefully . Signing off. Take care.
I don't think this guy realizes that you still have the stock part in place, you just covered them. Anyways the stock "felt" ones are visible from certain angles and look terrible after just a few contacts with pavement. I wish they were just plain plastic on the outside.
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