These old engine heads are sadly quite often in a rough condition.
A bit of petroleum paired with a copper brush, followed with a WD-40 coating, made it look pretty decent.
It couldn’t however hide the fact, that the restriction had been poorly removed.
Furthermore the threads in both bolt holes had been stripped.
One bolt hole was fixed by drilling, tapping and inserting a 6 mm helicoil, all done by the book and working as intended.
The other one however looked as if something had gone wrong during the process, forcing the former owner into tapping a larger hole. The hole had a diameter of 10 mm and had been double helicoiled. One large helicoil with a smaller 6 mm helicoil inside.
The idea was good, but it sadly couldn’t cope with my intended torque of 8 nm, so I had to find another fix for this. After a bit of research, where I read about big-serts, twinserts and other costly possible solutions, I finally managed to find a more simple one; a solid threaded bushing, with an outer diameter of 10 mm and an inner diameter of 6 mm.
The carburetor intake manifold is now properly tightened with a torque of 8 nm and I couldn’t be happier.