I think I have to reinforce the under trays.

[Mr Ward]

ON a trip today up the m6, m62 there was a sudden rush of air from the front of the Z.

Pulled into a service station and looked under the front of the Z.

The front under tray had caught on a speed hump and loosened itself unknown to me as I set off on the trip. At over 90mph the wind generated from the modified bumper forced the tray off its mounts shearing the plastic where the bolts mount it to the bumper, causing it to slam to the floor as I changed lanes. While changing lanes as the tray dropped it caught hold of a cat's eye. This resulted in a shower of plastic out the rear of the Z. Upon pulling into a service station, I had to force what remained of the tray off by getting my foot underneath and snapping what was left of the tray free from the alloy cross member. The plastic tray held fast and refused to let go of one bolt on the alloy cross member. The only way possible to get the tray to relinquish its hold of the last bolt was to use friction from bending to snap off the bolt holder part of the cross member that held the tray in place.

So as a result I am now in need of the tray mounting plastic at the front of the bumper, the engine tray and the alloy cross member.

 

[grannyknot]

My car didn't come with the plastic tray, I'm guessing something similar to you happened to it, I drove it all summer with no cooling problems.
With the outrageous price BMW is asking for that tray I decided to fabricate one myself, it is more aerodynamic and stiffer, I think it cost about $20.00 for the materials.
I'll post some pics later if you are interested.

 

[Chris_D]

or you could just leave the undertray off altogether. i haven't had one on mine for 5 years with no adverse effects.
I don't usually drive in wet weather however but when I got caught in rainshowers on the motorway it didn't present any problems.
Leaving the undertray off will help you catch oil leaks early by being able to spot pooling on the ground, otherwise caught by the undertray.
Just an idea.

 

[NS66]

When I had my Z resprayed a couple of years ago the bodyshop broke my undertray - they replaced and believe it was about £80. didnt think that was too bad?

 

[Mr Ward]

I'll post some pics later if you are interested.

I am definitely interested.
I have been toying with the idea of building one out of 2mm aluminium sheet with folds in it plus bracing runners for stiffness and rigidity also to stop it flexing. The added benefit of aluminium sheet would be adding additional support brackets to hold it up better at the sides of the engine bay with the amount of wind pressure in the engine bay from the modified bumper. I have an aluminium welder in the shed so constructing one shouldn't be too hard a job to build it with supports. The only drawback I can see is I would need to get hold of a tray and connecting plastic as a rough template to design it. The tray and plastics that are in the boot of the Z are a little bit snapped and mangled.

or you could just leave the undertray off altogether.

It's a preference thing that I'm sure you can appreciate, I'm a firm believer in if it's meant to there then it has to be there.

 

[PDJ]

 

[mmm-five]

https://www.ebay.com/itm/374105765922

 

[grannyknot]

When I had my Z resprayed a couple of years ago the bodyshop broke my undertray - they replaced and believe it was about £80. didnt think that was too bad?

You guys in Britain seem to get pretty good prices on things, that same tray would set me back about $550 CND, so making it myself was really the only option for me.

I'll post some pics later if you are interested.

I am definitely interested.
I have been toying with the idea of building one out of 2mm aluminium sheet with folds in it plus bracing runners for stiffness and rigidity also to stop it flexing. The added benefit of aluminium sheet would be adding additional support brackets to hold it up better at the sides of the engine bay with the amount of wind pressure in the engine bay from the modified bumper.

All 4 pics are at various stages as I was still cutting to fit it better. I just took the measurements of all the mounting points for the tray and mapped it out on the garage floor and cut the aluminum to fit, the straps are glued and riveted and make quiet stiff.

 

[Mr Tidy]

Chris_D wrote: ↑Mon Nov 21, 2022 1:20 pm
or you could just leave the undertray off altogether.
It's a preference thing that I'm sure you can appreciate, I'm a firm believer in if it's meant to there then it has to be there.

A forum member with a facelift ended up with a sump leak due to corrosion. His car hadn't had an undertray for a while - whether that was a factor who knows, but it must have been due to rust from the exterior!