How to Fit the E9X M3 Belly Pan to the E8X 1er

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CalvinNismo
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How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by CalvinNismo »

This is how to fit the structural M3 belly pan to your 1er. The benefits of this are increased structural rigidity of your front end, with better suspension performance as a result. There will be 2 ways of doing this, the full belly pan and the front only trimmed belly pan.

YOU MUST HAVE A HYDRAULIC POWER ASSISTED STEERING RACK!
The electric motor on the electric power assisted steering rack hangs below the subframe and would clash into the M3 belly pan severely. You can chop away a lot of the pan to accommodate this, I don't know how effective this would make the belly pan though, or you can convert your steering rack.

The Full Belly Pan, AKA option 1.

Image

Parts you'll need:

1 OFF - Reinforcement Plate [31 10 2 283 032]
5 OFF - Hex Screw with Collar (M10x33-10.9) [33 32 6 768 354]
4 OFF - Blind Rivet Nut, Flat Headed (M10) [07 14 7 199 279]
3 OFF - Plug-in Nut (M10-10-ZNS3) [31 10 6 779 393]
2 OFF - M10 x 50mm Grade 10.9 Bolt
2 OFF - 10mm to spacers to suit M10 bolts (front)
2 OFF - 18mm to 20mm spacers to suit M10 bolts (rear)

Tools/equipment you'll need:
- Jack and axle stands or a ramp(s)
- 8mm socket/spanner
- 16mm socket/spanner
- Torque wrench good for 60Nm
- Rivet nut tool (alternatively, impact gun with sacrificial strong part with a roughly 10.5mm hole in it and a sacrificial M10 bolt)
- Dremel, die grinder or a drill suitable for aluminium
- Needle nose pliers

The undertray will not fit without significant modification.

1. Mark your belly pan like so and remove material as shown. You don't have to remove the frontmost tabs, but they have no use. I assume they were to hold the flat aluminium sheet during the stamping process. If you are using a Dremel or a die grinder, be careful, it bites really easy! I'd recommend drilling and then slotting the hole for this reason.

Image

Image

Image

2. Get your 1er up off the floor enough for you to comfortably be able to get underneath with room to work.
3. Remove the main undertray underneath the engine, there are lots of 8mm hex head bolts holding it on, then remove the 2 aluminium brackets that come down to meet the undertray.
4. Pull the 2 pins either side of the jacking point down towards the floor, removing them from the jacking point.
5. Pull on the jacking point towards the floor, it shouldn't be too difficult to remove.

Image

6. Insert the plug-in nut in the slot in the subframe underneath the jacking point.

Image

7. Mount you belly pan through the hole in the jacking point and you will see which of the hexagonal holes you need to insert the rivet nuts into.

8. Insert the rivet nuts into the necessary hexagonal holes in the subframe. I tried first of all with a rivet nut tool, but these rivet nuts are steel and they are beasts! It started the rivet nut, but the tool felt like it was going to break, I then did the others with a machining block and an impact gun. All you have to do is start the rivet nut so it holds itself in the hole, it will then pull itself into place as you tighten the belly pan on when you fully mount it. The beauty of hex rivet nuts!

9. Insert the plug-in nuts into the slots at the rear of the subframe.

10. Mount your belly pan, with the 10mm spacers at the front and the 18mm/20mm spacers at the rear. The 50mm bolts are for the rearmost holes.

Image

11. Torque all 7 bolts to 56Nm, then add 90 degrees to each.

12. If you want to refit your undertray, I can't help you here.

The Trimmed Belly Pan, AKA Option 2.

Parts you'll need:

1 OFF - Reinforcement Plate [31 10 2 283 032]
5 OFF - Hex Screw with Collar (M10x33-10.9) [33 32 6 768 354]
4 OFF - Blind Rivet Nut, Flat Headed (M10) [07 14 7 199 279]
1 OFF - Plug-in Nut (M10-10-ZNS3) [31 10 6 779 393]

Tools/equipment you'll need:
- Jack and axle stands or a ramp(s)
- 8mm socket/spanner
- 16mm socket/spanner
- Torque wrench good for 60Nm
- Rivet nut tool (alternatively, impact gun with sacrificial strong part with a roughly 10.5mm hole in it and a sacrificial M10 bolt)
- Needle nose pliers
- Grinder, with cutting and flapping discs
- Files for aluminium

1. Trim your belly pan like so, this isn't easy to make look nice, so take your time.

Image

2. Get your 1er up off the floor enough for you to comfortably be able to get underneath with room to work.
3. Remove the main undertray underneath the engine, there are lots of 8mm hex head bolts holding it on, then remove the 2 aluminium brackets that come down to meet the undertray.
4. Pull the 2 pins either side of the jacking point down towards the floor, removing them from the jacking point.
5. Pull on the jacking point towards the floor, it shouldn't be too difficult to remove.
6. Insert the plug-in nut in the slot in the subframe underneath the jacking point.
7. Mount your trimmed belly pan through the hole in the jacking point and you will see which of the hexagonal holes you need to insert the rivet nuts into.
8. Insert the rivet nuts into the necessary hexagonal holes in the subframe.
9. Mount your trimmed belly pan.

Image

Image

10. Torque all 5 bolts to 56Nm, then add 90 degrees to each.

11. Re-mount your undertray, you won't be able to put in 4 screws. I may look into adding some extra fasteners back into the mix in the future, through or into the belly pan itself.

Image

You'll have these left over.

Image

Enjoy the extra rigidity your front end now has!
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by Nyxeris »

Great writeup!

Another thing added to the "one day" list haha.
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by docwra »

Legendary work mate, Ill let you know how I get on fitting mine :thumbs:
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by jonwilli »

Thanks for the write up, great addition to the 1er community. Such a simple mod really and staring us in the face on RealOEM, I can't believe it hasn't been undertaken more. It even seems fairly uncommon even in the US where they are super mod hungry. I have an M3 belly pan for the 130i ready to go on in the next few weeks :thumbs:
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by Ja50nK »

Fantastic write-up. Well done

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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by jonwilli »

docwra wrote: Thu Apr 01, 2021 10:44 am Legendary work mate, Ill let you know how I get on fitting mine :thumbs:
Hi Docwra, Calvin has kindly sent me the spacers he made to fit the full belly pan, Option 1. Last night I was playing with fitting the second hand pan I bought and decided that I would trim the pan like option 2 above. Let me know if you want the spacers and I can pop them in the post to you.
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by docwra »

jonwilli wrote: Fri Apr 02, 2021 7:06 am
docwra wrote: Thu Apr 01, 2021 10:44 am Legendary work mate, Ill let you know how I get on fitting mine :thumbs:
Hi Docwra, Calvin has kindly sent me the spacers he made to fit the full belly pan, Option 1. Last night I was playing with fitting the second hand pan I bought and decided that I would trim the pan like option 2 above. Let me know if you want the spacers and I can pop them in the post to you.
Haha, youve got to love this place, Calvin offered to send them to me as well :lol:

If its no bother that would be great, Ill PM you my address in a moment, cheers :thumbs:
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by CalvinNismo »

Ha ha, I didn't want the spacers to go to waste! If someone can make use of them, then they'll have been worth making!
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by Poormans »

How should we look at this.. front four bolts are all subframe.. rear bolt to the chassis?
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by CalvinNismo »

Poormans wrote: Wed Apr 07, 2021 3:18 pm How should we look at this.. front four bolts are all subframe.. rear bolt to the chassis?
All of the bolts go into the front subframe for both option 1 and option 2. If you look just to the left of the down pipe in the image below, you'll see one of the plug-in nuts at the rear of the subframe. That's where the rearmost mounting points of the belly pan would go to, similar(ish) to how it is on the E9X M3.

Image

The front section of the belly pan braces between the frontmost crossmembers of the front subframe, right where the front suspension arms mount to, so it stiffens right where those forces are acting on when cornering. Bracing across the rear as well would be great, I will look into viability the E9X non-M V-brace to see if there are mounting points when I next get a chance to get under the car.
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by Poormans »

So the rear 2 mounts are probably not adding any stiffness..? Also curious as to whether a v-brace will fit. To share the fr/aft load just like the rear. Not so clued up on exploded views, but will the 1m tell us anything? Or the 135i convertible?

Good thing I squirreled that 1m rack as currently there's epas fitted!
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by Poormans »

Hmm had a look on real oem, 1m doesn't seem to have the bellypan..
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Re: How to Fit the E9X M3 Belly Pan to the E8X 1er

Post by CalvinNismo »

The 1M doesn’t have a belly pan, no, it uses the same front subframe as all non-convertible non-M E8X and E9X. If you think about the subframe being a capital ‘A’ shape, it’ll definitely be worth bracing all of it, if possible, however it’s only ‘easy’ to brace the front section of it, otherwise the M3 belly pan sits off too much as it’s not designed for our subframe.

The E88 does have V-braces and looks like the below image.

Image

The E88/E93 share a common subframe that has mounting points welded to the front of the subframe, which you can see in the above picture. As far as I know that is the only difference between the 2 subframes. The welded on mount also sits lower, probably to straight line the V-braces. At the front of that welded on part, there is also a central mount for 2 diagonal rods (similar to the strut brace at the bulkhead) that go up to the chassis leg/rails, however there are studs that are welded on to only the E88 rails, so you would have to weld these studs to your chassis legs/rails, which would probably be an engine out job. I have looked into this as I wanted to do it. The diagonal rods are engine specific.

There is an early E93 machined piece that you can bolt onto regular subframes (P/N: 51 61 7 135 640).

Image

You would then need specific early E93 V-braces I believe, but even then they are not plug in and play and require tabs welding on and/or holes drilling. This is however the best solution for those with EPAS, if you don’t change your rack.

There is some information in this thread about it:

Strut Bar (E88 Specific)
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