Undertray fixings

[BoxsterLL11]

I am giving my Boxster a good going over while its fully up on axle stands and doing its 12 year service.
I have removed all the undertrays to give them a clean and remove the multitude of stones and gravel they have been collecting.
Unfortunately, three of the plastic nuts which is one type of tray fixing has sheared off their threaded studs that are fixed to the underside of the body.
I have oodles of plastic fixings etc in my stock but as yet cannot find a way of reinstating a fixing to replace the sheared stud and plastic nut.
Obviously I will have to remove the remnants of the sheared stud from the underside of the body.
I just wondered if any other owner has experienced this and how they managed a fix.

 

[ianthow]

This is a common problem with these nuts and studs. Some places just trim off the remains of the stud and drill a hole for a self tapping screw. I prefer to use rivet nuts, e.g. https://www.amazon.co.uk/dp/B0B57D1Y74?th=1 with M6x20 stainless steel screws e.g. https://www.amazon.co.uk/Stainless-Flanged-Button-Screws-Socket/dp/B0BK1X9X2P. You could use shorter screws, but I use the old plastic nut to make a large washer/spacer by cutting off the hex part of the nut and running an M6 tap through the remaining 'washer' then threading it onto the screw. I think this is better than using large 'penny' washers.
Note, you don't need a special tool to instal rivet nuts. Use an M6 screw with a large nut as a spacer (or drill out a smaller nut to 6.5mm). Add an M6 washer between the spacer nut and the M6 screw head. Press the assembly into the drilled hole (it should not be a loose fit). Use a spanner on the spacer nut to stop it, and the rivet nut, rotating and tighten the M6 screw. You will feel the rivet body expanding, keep turning the screw until it is solid. Practice on an old piece of sheet metal to check that a) the screw is long enough to fully engage into the rivet nut (if not get a longer screw) and b) to get a feel for the force required to collapse the rivet.

 

[BoxsterLL11]

Thanks Ian.
I have plenty of A2 M6 screws in my stock to be able to use.
Wasn't sure about drilling the floor pan for not knowing what is the other side.
Worth a go for £4.99 for 20 and free delivery.
3 sheared on different trays so not the end of the world if nothing is refitted but I prefer to fix it when its not right.

Also had one of the torx screws seized solid by the offside front wheel.
Sheared the tips of three torx bits trying to remove it, ended up grinding the head off then chisel the threaded section of the torx screw and the speed nut clip off the aluminium suspension sub-frame.
The screw wasn't seized in the speed nut but in the alloy sub-frame flange.

And got a dust pan full of small stones sitting on the top of the front tray !!!