I am replacing the two bolts at the rear end of the engine undertray (Mk1).
Perhaps stupidly I decided to take off the entire undertray. Sprayed on some penetrating oil, and most bolts seemed loose enough.
But I sheared off the bolt which connects the metal stay on the front valance to the underside of the engine bay.
Anyone got tips on how to deal with this one? I could try to get a set o grips on the little bit of bolt which is sticking out, but I don’t have much hope.
Would it be a bad idea to drill a new hole just to one side and use a self tapping screw to hold the stay in place?
Whatever you do, I’d try to use the original fixing point as it’ll be far stronger than a self tapping screw. So, if there isn’t much of the bolt left to get a set of mole grips on, I’d be drilling a pilot hole down the centre of the threaded remains and try to extract it. I tend to drill as much of the bolt thread out before getting a punch and hammer to tap the edge of the bolt inwards to collapse it inwards (hope that makes sense). You can then tap it round, unscrewing it with the punch and hammer until there is enough to grip with a set of pliers or mole grips.
From your description is it the lower of the stays for the front bumper that the bolt went through? If so you will need to raise the car a fair bit to get access, you need to drill the pilot hole dead centre (or near as) and drill straight.
If you don’t have the tools or access to ramps or a means to raise the car sufficiently, it may be worth getting a garage to drill the bolt remains out.
To drill out as described above is the ideal solution, if you have neither the skill or patience like me, I got the matching drills and self tapping bolts to do mine.
Yep, self tapper with a hex head preferably. Nice dob of copper slip grease to stop it seizing up again.
Those stays are to help prevent the bumper distorting under wind pressure at speed and are not really anything to do with load bearing. that`s why they are so thin.
Most of the screws and bolts corrode into place on the undertray and then shear off when an attempt is made to undo them. So you had areal result with the loose ones on your`s.
Any that do start to budge, you should wind back and forth to help clear the thread as you go. Again put them back in with a good dob of grease.
It`s all part of the FUN you know,not something to worry about.
A cheap set of extractors may be a good investment if you’re not keen on drilling the whole bolt out (not sure I would be underneath my car!)
Only had to drill one bolt out before (and not on my car) - I drilled a small pilot hole to stop the larger drill bit from slipping, then drilled it out with a drill bit 1mm smaller than the size of bolt I was removing. Cleaned the threads out with a spare bolt, then fitted the replacement and job was a good 'un.
The key is keeping the drill straight so as not to damage the threads of the hole, or at least to leave as much intact so that you can still fit a new bolt.
That “bolt” is usually a stud that protrudes from the chassis leg. When mine sheard off I drilled out the remaining thread, tapped a thread into the head of the stud that’s welded inside the chassis leg threadlocked a bolt in a few threads and cut the head off so I was left with a stud again.
Thanks for all the advice. I got a set of stainless bolts from Screwfix today, and a set of stud extractors.
As I recall it was a nut which sheared off in that location, so yes it is probably a bolt which is protruding from the chassis leg as Robbie says. Might not be an easy j
A quick update, if anyone is interested. I got my engine undertray off, but could not do anything with the two bolts on the crossmember which have sheared off.
One for a garage methinks! And as I discovered a small oil leak at the same time it may be worth a garage visit anyway.
The sheared off stud with the front wing stay has a little bit left on it, and I got an M6 ‘extension nut’ from Screwfix, which in intended to joint together M6 threaded rods.
I could see attaching the wing stay to the extension nut, but I think it may be too much leverage.