helicoil insert

I have recently helicoiled half a dozen stripped threads for screws holding the outer gearbox cover on my Velocette. Somewhat nervous because I had not previously done any before. Used hand held power drill (!!) but OK. Used 'V-coil' kit from eBay purchase. All went well.

Then did a larger much diameter one elsewhere. OK again.

Only problem is that the larger the diameter is, the more difficult it is to keep drill straight if doing it by hand. With my first ones which were 1/4", the drill followed the hole well enough. The second was for a banjo fitting and so had to be spot on. Done with pillar drill which took me ages to set up.

As said, problem is to drill and tap straight. Of course best done on a drill press or milling machine. But time consuming to set up straight on the machine table. Not everyone can drill straight with a hand drill. A trick I've used a couple of times is to make a metal block and drill a right size hole in it at a drill press. Hold the block on the workpiece and drill through it. Then the hole will be fairly straight. Personally I find it harder to tap than to drill freehand. So another block with a drilled hole at tap size. Done it on a car engine, which didn't fit on my mill.

The nasty bit of making it in situ is the small piece of the helicoil that you break off after screwing it in. Since it's stainless steel it's not catched by the magnetic sump plug. A bit worrying where it goes.

Did mine 25 years ago with hand held tools and a carpenters square , Stuff rags in the engine to catch tang .