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I’m sure we’ve all experienced it at some stage. Someone has hammered the bolt or stud to get an engine out and now the thread is mushroomed and the nut doesn’t fit.

How do you sort that one out?

The old methods would have been to run a thread-file over the threads to realign them, reshape the end with a grinder or maybe even to cut the end of the thread off with a saw if it was really bad.

£6 delivered from eBay, well worth having one
£6 delivered from eBay, well worth having one

How to fix it

You don’t need to do that any more thanks to the wonders of CNC tool machining. The modern solution to this conundrum is a simple conical cutter called a Deburring Tool or an External Chamfer Drill. You simply fit the tool to a drill, spin it clockwise a few turns and the cutter will put a nice gentle lead onto the thread, cutting through the mushroomed head.

VIDEO | Conical cutter

When can you use

  • Where this method works well is on larger diameter threads (M10 and over) of long studs and bolts.
  • It works best on softer fasteners. Stainless studs or hardened threads will not cut so easily or at all.

When you can’t use

  • The tool I bought does not work on small diameter threads (e.g. M6).
  • It can’t be used on short studs that only stick out of the casing by a small amount.

Where can you find one

Any of the main online marketplaces like eBay or Amazon. Simply search for ‘External Chamfer Tool’ or ‘Deburring Drill’.

Verdict

It makes short work of a previously common and slow to resolve problem.

The best tip is not to hammer studs out in the first place with a steel hammer. Use a copper faced one and a punch to remove it fully in future.

Words and photos: Sticky

Thanks to Paul Casey for the suggestion

Have you got the latest updated Spanner’s Manual? 

For more of the latest tips on engine rebuilds (including use of the Buzzwangle for ignition and port timing) see the latest edition of The Complete Spanners Manual – Lambretta Scooters.

Have you got your kit and scooter sorted?

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