Underbody fixings

Whilst doing the cables I removed the underrays and have noticed that a number of the fixing studs are in poor shape, one was missing actually. I've found some 15mm square stud plates in stainless and was planning on cleaning the old area up, zinc primer and resin epoxy a plate on then use a serrated flange stainless nut (I have loads of these). Anyone done this before? I'm assuming that is the right process and I'm also assuming some m4 x 16mm ones will be correct although I'm not sure if people use m5 ones? Any opinions or advice welcome

I've seen someone use the method you describe on here before, and it was successful as far as I can remember. I have similar problems with crusty underbody studs, and have bought the same stuff as you to tackle the problem. However, I was discussing it with my local welder and he mentioned they have a machine that welds on new studs without needing access to the back side of the bit being welded to (apart from to remove anything that might melt. He said it was pretty cheap and they could weld on stainless studs. I'm considering whether to take this option instead. The welding shop in question is Ashby Welding in Church Crookham, Fleet. I highly recommend them, and use them for lots of small jobs. Always fast, always flawless quality, and always cheap.

That's interesting that that's a possibility. My thought was that as adhesives have improved they're now an acceptable replacement for welding in this application. Ferrari and McLaren stick their entire cars together!!!

I have just done a full restoration of the under side of my 996. I cut small pieces of 2mm plate at 15x15mm or 20x20mm. Can't just remember which. 6mm hole in the centre. I welded an m6 bolt in and cut the head off. A splassh I'd weld through primer and welded them on. I have the carpets lifted already as I had a lot of welding to do. The biggest problem with the idea of just welding a stud on as Martin said is that the floor around the stud rots with the stud. Not always a problem but never great. My idea is fine for the undertrays as they just need nuts and washers. Not so good for all of the pipe fittings as the bolt doesn't fit through the fixings so I've had to get a little creative.

That sounds good although with my welding ability there'll be no floor left after I've burnt through it!!! I welded the control box onto the leg of the ramp when I moved it?!? I ended up taking it back off and asking someone to do it for me!! It was on but what a mess!!

Welding galvanised bodywork isn't easy as it spits a lot. I had to make new outer and inner sills and rear arches. Not easy by any stretch but a good leaning process. The most valuable lesson learned was to check the car over better before you buy. :floor:

Mentioned this on a different thread - may be a solution for those that can't or don't want to weld - bighead studs are a coachbuilding alternative. The flat with the small holes gives a large bonding area, with the advantage that the bonding solution passes through the holes to effectively grab from both sides. After cleaning the mounting surface, attach with a 2K adhesive or something like Sika 552 or 555. Bigheads available in various sizes.

Exactly what I'd mentioned! In fact I've ordered 100 15mm square m5 x 12mm ones. I think I'll do most of them again and then they're all right! Planning on cleaning up the surface and using some loctite quick epoxy with it taped round to make it neat and then spraying with zinc primer and then under seal. Should make a tidy repair and safe going forward. For those interested 100 were about £60

I assume you won't need 100, do you fancy selling some of them on to recoup some of your costs? Mike

Of course, I'll have a count up when they arrive and I'll let you know.

Thanks

I have a similar problem with the rear exhaust heatshields stud fixings. I've ordered some rivnuts as per the link below, would be interesting to see how you get on. http://911uk.com/viewtopic.php?p=1389665

I have loads of rivnuts, use them on the motorbikes, very useful if needing a fixing into a subframe. Always use the serrated ones not the smooth ones, I just didn't fancy drilling loads of holes!

You can get rivstuds actually. I've never used those but same principal, drill a hole, fire the fixing in and you've got a secure stud, like I say only thing been you have to drill the underbody.

I don't fancy drilling holes either, please let us know how you get on & if you want to sell me 10 of those M5 studs.