Self Tapping Screws into new Metal?

[richardACS]

https://www.ebay.co.uk/itm/BMW-EXPANDIN ... xyzpdTiM99

Just getting to the point of drilling holes into new metal panels throughout for the myriad of posi drive self tapping screws prior to the body going in to paint. The thought of drilling and screwing metal to metal seems like a recipe for future rust and wonder if others have come to a decision whether to stay original or install these plastic grommets?

I can't say the plastic grommets are always the answer as rust around the square plastic blocks occurred on my 15 year old BMW which uses the above blocks, I guess the paint is so thin on the edge of a hole the plastic takes it off any way when just pushing them in!

Also the square blocks are a pain to file into shape in the first place and to keep them close to spec, so the blocks are either not too loose or too tight!

Has someone found a neater idea? and are there round plastic grommets so drilling could be fast and accurate - even though future removal would have them spinning

The other problem of course is that by using a plastic grommet the item will be sitting pround by 1 or 2mm which is going to look naff and possibly cause the item to work loose if it has no mating surface to add to stability?

[111Robin]

You could try rivnuts. It means using machine screws instead of tappers but certainly avoids the corrosion issue.

https://www.ebay.co.uk/itm/M4-4mm-Brass ... 2732206667

[Catmint]

Can you get away with rivnuts ? - are available in stainless as well

[Catmint]

You could try rivnuts. It means using machine screws instead of tappers but certainly avoids the corrosion issue.

https://www.ebay.co.uk/itm/M4-4mm-Brass ... 2732206667

you beat me to it

[111Robin]

You could try rivnuts. It means using machine screws instead of tappers but certainly avoids the corrosion issue.

https://www.ebay.co.uk/itm/M4-4mm-Brass ... 2732206667

you beat me to it

I have an early Elise and all of the body sections are held on with these rubber rivnuts, they don't require huge forces to compress them so should be fine for general use on steel panels and avoid any metal to metal contact.

[richardACS]

The rubber head rivnuts are a nice idea but I wonder if the upstand is going to present some problems to causing the fixed item to 'stand off'? (where I've seen these used there is a rebate to allow for it). What do you think robin? lets for example consider the grille moustache, windscreen bottle holder, the CAS numbered plaque by the top of the radiator, window felt strips in the doors?

But it's got me thinking about the aluminium rivnut which is compressed in like a pop rivet and has very little upstand and commonly used in race cars - these might work with a good dollop of waxoyl between the mounting surfaces - any thoughts?

[Tupers]

I would opt for a steel rivnut. They don’t need as large a joke as the rubber ones and the threads are more robust than the aluminium ones.

If you can get them in before paint the car I would recommend drilling and deburring the holes then painting the nuts in zinc rich primer immediately before fitting. That way there will be no bare metal inside the hole.

[richardACS]

Tupers thank you, that is a sound suggestion.

I do have a rivnut kit and just dug out a few M3 and M4 nuts in steel. The upstand is .5 mm and .6 respectively and the drill dia would be 5mm and 6 respectively so not large holes.

I've ordered some posidrive pan heads bolts to see whether the head dia could match dims of the original self tappers and see if there is any tangible stand off of say the grille and moustache.

Have to consider whether best to fit nuts before or after paint, presently the body is in primer...

[Spider]

I tend to use a lot of Rivnuts in my builds, I fit them in before paint and then run a tap through after to clean up the threads. Sorry, but I would recommend against Stainless or any dissimilar materials as they can cause the adjacent steel to rust or the rivnut to corrode (depending on what metals they are), I have found Zinc Plated to be the pick.

Just be aware though, while Rivnuts get around some issues, when they go wrong, a rusted screw in them cross thread, wrong thread etc, they can make a huge mess of the paint. If they are somewhere that's blind on the back, they will be one of your worse nightmares.

In some instances, after fitting the rivnut, I'll put a little longer screw in from the back so you end up with a stud.

[111Robin]

Yes the downside is if the screw becomes seized and the rivnut spins when trying to remove the screw. However if properly lubricated on assembly the risk is low. I had several on the Elise that spun (factory assembled with no lubricant) and had no option other than punching them through into the closed void behind. All I could then do was pump in a load of grease to stop them rattling around inside the sills. I like the idea of fitting them before paint though, far better than a self tapper if the standoff doesn't cause any fit issues.

[GraemeC]

In some instances, after fitting the rivnut, I'll put a little longer screw in from the back so you end up with a stud.

Would a rivstud not then make more sense? or are there other drawbacks?

[Spider]

In some instances, after fitting the rivnut, I'll put a little longer screw in from the back so you end up with a stud.

Would a rivstud not then make more sense? or are there other drawbacks?

Yes, but for the few I do, I'm not buying 100 of them

It also has the advantage that I can effectively make any length stud I need.

[GraemeC]

Ah - the ones I got were in a much lower quantity (although no doubt I paid for the privilege). I do find them more secure than a rivnut with back fed machine screw through, and obviously can be used blind.

[Spider]

Ah - the ones I got were in a much lower quantity (although no doubt I paid for the privilege). I do find them more secure than a rivnut with back fed machine screw through, and obviously can be used blind.

I hear you on that Graeme, if I know what length I want to end up with, I'll either use a lock nut or Red Loctite.

I have also fitted them in Blind holes too by fitting the screw, grinding the head back to the same Dia of the Insert and then fit, using a Nut and Washer to compress the insert.

And that just reminds me why I don't but Studserts - Ideally, I'd need another tool, doing them with a Nut isn't the greatest.

[agricola]

Despite the cost these are very good value for money.
https://memfast.co.uk/shop/Vprod1.asp?cat=2258004632

[richardACS]

That is a nice tool for those difficult to reach areas where the big hand tool cannot operate!

Interesting views on rivstuds...

[agricola]

Compared to the pliers pull type these are in a different league you tighten them with a spanner so you can feel the tension cant get them in everywhere but very good.

[mk1]

Am I missing something here?????

It is incredibly rare to find a car rotting round a self tapper hole, even less common to find a car has rotted away from this point. It is almost unheard of because all the fasteners are zinc plated. This will protect fastener & panel.

Replacing standard self tappers with 1001 rivnuts just seems totally BONKERS to me. Not only will it look weird, but It won't solve the original problem. You will still have metal to metal contact that will under some conditions allow corrosion.

OK, the rubber rivnuts described in an earlier post will stop this totally, but in most positions, it will look crap!

None of us like rust, but these cars have lasted 60 or so years & are broadly speaking still intact, we have to accept that a construction of steel with aluminium components fitted to it will to some extent be prone to corrosion, it's a fact of life., worrying about issues like self tapper holes strikes me as about as sensible as discussing how many angels you can get on the head of a pin!

[111Robin]

Personally I think it's a decent idea. Self tappers are the cheapest and quickest method for attaching to a panel but certainly not technically a great solution. I doubt there are many cars built today with screws straight into steel panels. The plating on the screw and paint on the panel disappears as soon as you screw it in so doesn't prevent corrosion. How many boot lids have you seen with dirty big self tappers holding on the number plate, out of sight but lurking behind is a nice big blotch of rust working its way outwards from the screw. Granted the car won't dissolve but it does end up a pain in the arse after a few years. Plus if it's something regularly removed like a grille the holes eventually become enlarged and the screws won't tighten so you end up caving in a bigger screw that looks like shit. You won't see the rivnut anyway once assembled so don't see why that would be an issue. On the Elise everything is held on with rubber rivnuts including the body panels. They could have used self tappers but chose not to thankfully. If I were building up a newly restored shell I might consider using them in certain places but I'm not going to start changing them out now. It's definitely one for the perfectionists which is fine by me.

[GraemeC]

You raise good points Mark. I think for me, the choice of a rivnut over a self tapper comes down to how often I think I may need to disassemble the joint as a self tapper into a hole inevitably gets looser every time.