The Classic Motorcycle

Broken tap solution


Tim Britton’s story of the broken off tap imbedded in the clutch of his ‘Project Triumph’ (TCM, June 2022) prompts me to write about a repair process that a friend of mine put me onto 10 years ago.

My problem at the time was a snapped off and seized mudguard retaining stud in one of the lower front fork legs of an Ariel Red Hunter. Replacemen­t Ariel lower fork legs don’t grow on trees and are pricey if you’re lucky enough to find a good one, so I really wanted to save the one I had.

Personally, I shy away from the so-called ‘easy outs’ that Tim mentions. A stud/bolt/tap/etc seized in tight enough to have snapped off is unlikely to come out using a screw extractor. You’ll more probably end up with a broken ‘easy out’ wedged inside the snapped piece, with both still jammed in the hole, too.

Tim’s last resort, involving the sacrifice of some threads by punching the offending piece out from behind with a hammer, is too brutal and damaging for a sensitive person like me to even contemplat­e. The hightech answer, as suggested by my friend, is to take the part to a workshop equipped with spark erosion technology.

This works by passing a highly focused electric current between an electrode and the broken piece submerged in a dielectric liquid. The flow of electrical energy produces a small puddle of molten metal in the end of the piece, from which droplets come off as sparks as it is progressiv­ely and precisely eaten away by the current (Google it!).

The technology certainly worked on my Ariel fork leg, leaving a clean hole with no loss of thread depth. Maybe the cost couldn’t be justified for Tim’s clutch, but for hard to find and valuable parts, I’d certainly recommend it. The attached photo shows my Ariel fork legs restored with all new internals – bushes, stanchions, springs and oil seals supplied by Draganfly, along with a new mudguard retaining stud in the cleaned-out hole.

Lawrie Bradly, Melbourne, Victoria, Australia.

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