Helicoil

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Helicoil

Postby mikeydpippin » Wed May 06, 2020 8:35 pm

I’ve got a thread of the Carb manifold bolt broken in the cylinder head, rather than take it to the engineering company I thought I’d helicoil a new thread.
The bolt i believe is the one shown 010625 (I have a bolt but the part number is a stud)
What helicoil kit will I need is it the 1/4” UNC
Thanks in advance.

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Re: Helicoil

Postby dave16mct » Wed May 06, 2020 9:21 pm

You need to look that part number up in an earlier part list to find the length and threads (and it won't be UNC!). You only Helicoil to repair a stripped thread. For a broken-off stud I carefully centre-punch, then pilot drill. Then a slightly bigger drill. Sometimes you can knock a square tapered tang in and unscrew it. Usually you have to keep on with slightly bigger drills untill you can see the thread. Sometimes it comes out in one piece, sometimes you have to pick it out with a scriber or similar. Don't use an 'easy-out'. It'll probably break off and leave the hardened piece stuck in the hole!
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Re: Helicoil

Postby Mick D » Thu May 07, 2020 5:56 am

Hi

I'm guessing the thread will be 1/4" BSW in the head and 1/4 CEI for the carb attachment nut - someone please correct me if I'm wrong :)

In which case, to repair the thread in the head you need one of these:

https://uni-thread.com/tr_bsw_kits_detail.php?00718-3

In an ideal world you'll have a drill press with a capacity large enough to accept the head for drilling and a means to clamp the head in position on the drill press table, (the repair 'can' be carried out in situ but it's not something I'd recommend for a first timer). You'll also need a suitably sized tap wrench.

Regards Mick

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