1955 Model 150D - stripped thread on handlebar clamp

[Big Al]

One of the two threads in the lower half of the handlebar clamp has been stripped, and a larger thread cut (which appears to be imperial!). The problem is that a larger bolt will not pass through the hole in the upper part of the clamp, to engage the thread in the lower part and pull the clamp tight.
Looking on the internet and U-tube, I think a helicoil insert of 9 x 1.25 and 7mm long will accept the original chromed bolt.
Is there an alternative way of doing this, as I don't have the necessary tools myself? There is not room to put a normal nut on a longer bolt, and in any case that would not look original.
If not, I will need to find an engineer who can do it, as I would like to keep the original part, rather than just buying a whole new clamp, made to the original pattern - the easy way out!

[Rob Miller]

The threads are 8x1.25. Any good scooter shop should be able to fit an insert for you.

[Big Al]

Many thanks Rob. Yes, 8mm not 9mm

Happy Christmas to you, and all LCGB members.
Alan

[mm man]

Happy Christmas to all
I have sent you a pm if you get stuck
Cheers

[jbcollier]

Amazon and ebay have inexpensive thread insert kits.

[Big Al]

Yes, I saw this one John: ZXX 30pcs M8 x 1.25 Thread Repair Kit for just £10.59, but wondered if the length, 8mm, might be too long. I read that the insert should sit slightly down from the top surface, or isn't that important?

Also, another larger thread has already been cut, maybe for an insert, but there was no insert there when I stripped down the scooter. That might make it possible just to wind in another insert. How can I check this first?

MM Man: Many thanks for your pm and kind offer.

[jbcollier]

You can trim down a thread insert that is too long with a dremel cut-off disk.

Yes, the insert should be slightly below the surface as it is a lot harder than the surrounding aluminium.

Can't comment further without seeing photos of the problem. It "might" be the case that an insert was already put in place and then lost. In that lucky case, you could just wind in another insert. Holding your breath on that being the case is not advised. It could also be repaired by shrink-fitting a solid aluminium insert and then drilling and taping a new threaded hole. Any competent machine shop could help you with that.

[Big Al]

Thanks for the helpful suggestions.
There are a few places I can think of here in Brighton & Hove that I could try, but the likes of Blabers, Speedway Motors and individual scooter workshops such as Gerry Ingram's, which were in business during the 1960s, are of course long gone.
In the meantime I have plenty of other work I can do to get the 150D back in one piece again.