Under Tray screws
Discussion
Take the old screw to somewhere like Bapps bolts, i believe it is a 3.5 mm hole in the chassis and the thread on the screw need to be 4mm overall in diameter, i would order between 12mm to 16mm long, they really do not need to be long, you are going through about a total of between 4mm to 5mm of material, these size of screws have pretty much been used througout the entire car, they are same on the wheel arch splash guards and almost everywhere.
Where the diffuser connects to the engine underpan, i would get 5mm diameter, so that they re-bite better into the fibreglass.
Where the diffuser connects to the engine underpan, i would get 5mm diameter, so that they re-bite better into the fibreglass.
Just got in from the garage having re-fixed mine. I used SS hex head self drilling 4.2 x 16mm with M4 nylon washers. You don't really need self drilling for this aplication but it makes it easier to locate and start them. As Chris says they are slightly larger (but shorter) for the tray to diffuser, I've bought 4.8mm x 13 and have loads spare of this size if you want some as I had to buy in bulk.
Hi Andy
Here is the link
http://www.shop4fasteners.co.uk/acatalog/Self_Dril...
As you can see quantites are on the high side but you need a lot of the 4.2mm size for the tray and I will use more when I do the rest of the flooring but as I said I have more 4.8 than I will ever need so you can have some of them if you want.
One other thing I read was to always lubricate ss fasteners so I used some copaslip on them.
Rob
Here is the link
http://www.shop4fasteners.co.uk/acatalog/Self_Dril...
As you can see quantites are on the high side but you need a lot of the 4.2mm size for the tray and I will use more when I do the rest of the flooring but as I said I have more 4.8 than I will ever need so you can have some of them if you want.
One other thing I read was to always lubricate ss fasteners so I used some copaslip on them.
Rob
Edited by Rob_W on Wednesday 16th February 20:58
Rob_W said:
Just got in from the garage having re-fixed mine. I used SS hex head self drilling 4.2 x 16mm with M4 nylon washers. You don't really need self drilling for this aplication but it makes it easier to locate and start them. As Chris says they are slightly larger (but shorter) for the tray to diffuser, I've bought 4.8mm x 13 and have loads spare of this size if you want some as I had to buy in bulk.
Ooh there not very aerodynamic screw heads them rob 
Andy,
I did have the same problem with one batch of S/S screws, the heads were just twisting off, i cant remember where i got them from, but the next batch i got from Bapps bolts, i believe they have stores nationwide, the screws from them must have been a stronger grade because i never had the problem again or since, i got lots spare so whenever i round one off a little i replace it for a new one, but when the heads twist off they can be a right bugger to get the shank back out, i learned that the best way to deal with this situation was to punch them through and then use a 4.8 screw.
R0162 said:
Ooh there not very aerodynamic screw heads them rob
I knew somebody would say that! Maybe I should try the Spitfire and peas experiment to work our how important it is?I had to slot 80% of the old screws with a dremel to get them out and didn't want that pain again!
I have got some decent button heads from A2fasteners (Stigs http://www.a2stainless.co.uk/default.aspx) which I have used elsewhere and may change to these.
Edited by Rob_W on Thursday 17th February 07:25
Edited by Rob_W on Thursday 17th February 07:28
Mike,
Just done this exercise,you need No 8 Pozi Flange (nice flush heads) stainless Steel S/tap 5/8" long.The originals were un neccesarily long.If it's the engine undertray on mine approx. 12 were a size No 10 as above.My supplier was www.spaldingfasteners.co.uk excellent next day service, good quality and nice people. Tip ALWAYS assemble S.S. with a copper grease on the threads.Hope this helps.
Haydn.
Just done this exercise,you need No 8 Pozi Flange (nice flush heads) stainless Steel S/tap 5/8" long.The originals were un neccesarily long.If it's the engine undertray on mine approx. 12 were a size No 10 as above.My supplier was www.spaldingfasteners.co.uk excellent next day service, good quality and nice people. Tip ALWAYS assemble S.S. with a copper grease on the threads.Hope this helps.
Haydn.
Haydn W said:
Mike,
Just done this exercise,you need No 8 Pozi Flange (nice flush heads) stainless Steel S/tap 5/8" long.The originals were un neccesarily long.If it's the engine undertray on mine approx. 12 were a size No 10 as above.My supplier was www.spaldingfasteners.co.uk excellent next day service, good quality and nice people. Tip ALWAYS assemble S.S. with a copper grease on the threads.Hope this helps.
Haydn.
Great advise,Just done this exercise,you need No 8 Pozi Flange (nice flush heads) stainless Steel S/tap 5/8" long.The originals were un neccesarily long.If it's the engine undertray on mine approx. 12 were a size No 10 as above.My supplier was www.spaldingfasteners.co.uk excellent next day service, good quality and nice people. Tip ALWAYS assemble S.S. with a copper grease on the threads.Hope this helps.
Haydn.
Ordered the flanged screws today and I will take your advice and put copper slip grease on each screw.
Thanks
Haydn
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