I am in the process or recommissioning my +2 130/5 (which I have owned for nearly 46 years). The nearside bobbin in the body to which the bonnet/pivot bolts has had the thread stripped, as has one of the bobbins in one of the headlamp pods.
If I really needed to I could cut out the headlamp bobbin and bond in a new one, but this would be time consuming and I would have to be extremely accurate - I would prefer not to. To do the same for the bonnet mount in the body does not even bear thinking about in view of the confined space etc.
I can’t think I am the first to have this problem and I would be interested to know how anyone else has got around this please.
All constructive suggestions gratefully received!
Thanks Al
You could just use a helicoil kit, plenty of space for the bonnet bobbins, might need a right angle drill adaptor for the headlight.
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FWIW, I had always thought Helicoil were a bodger’s product, only really suitable for repairing a stripped thread on a lawnmower engine, however my aerospace engineer son tells me that they use Helicoil as a matter of course where high strength reliable fittings are required. Apparently the result is better than screwing in to the original parent metal. The hole is tapped to accept a Helicoil and an insert fitted during manufacture.
Given this, a bobbin with an insert is probably a better fixing than it was when it left the factory.
Commonplace in Motorsport too, threads in Aluminium are rubbish.
This post has got me thinking about doing all of the bobbins on my S3 now the body is off.
Thanks Andy. I have never used Helicoil (but had seen spark plug threads treated this way on a Willy Jeep cylinder head which seemed a bit weird). I will check out the size and look for a small Imperial version.
Thanks and regards
Alastair
Without doubt use a helicoil. All of the bobbins in the body to chassis mounting were stripped in an earlier bodged restoration. I replaced them all. It’s fairly easy and quick and should be no problem with headlight bowls and bonnet mountings. Buy a helicoil kit off eBay but make sure to get one from a reputable supplier, I suggest Spalding Fastners or Kay’s. You want a 1/4 x20 UNC kit.
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I have just been using Helicoils to repair some threads in plastic. Helicoils if installed properly are OK in soft materials and light loads. I dont like using them for things that you will tighten and undo regularly. I prefer the solid type inserts that screw in and then pins lock it in place (Keenserts etc). These are more expensive and you need more material around the hole as the insert diameter is bigger.
Helicoil is more than adequate for that job. Timeserts are stronger but overkill for that and much more expensive
Alternative to thread inserts is to drill through and use a longer bolt with penny washer and nyloc nut at the emerging end…Tony
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Make sure you buy Helicoils that are long enough, standard ones are very short
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Personally i would fit a solid threaded insert, but as an easy fix could you bond another bobbin or threaded item behind and use a longer pivot bolt ?
They’re so common that my local hardware store (NOT a big-box version) stocks a whole section of helicoils in both SAE and metric sizes. i did all 16 of my Europa rear hub carriers (aluminum) in 5/16-24. Easy, just drill the holes straight.
The keeninserts seem to be excellent solutions for stressed situations in aluminium. My engine rebuilders havr used them as a matter of course for exhaust bolts/studs.
Tim