The hand-spin test

Lift the carriage clear of the rails, or tip the machine safely, and spin each wheel by hand. A healthy wheel turns several revolutions freely and silently. One that stops immediately, feels gritty or makes noise has a failed bearing.

Do this whenever you clean the rails. It takes a minute and catches the problem before the wheel starts damaging the rail.

Flat spots and material wear

A wheel that has sat under load in one position for a long period — a machine stored unmoved for months — can develop a flat spot. It produces a regular tick at the same point in every carriage stroke.

Polyurethane wheels also wear down gradually. When the carriage sits noticeably lower or contacts something it should not, the wheels have lost diameter.

  • Wheel does not spin freely and silently by hand
  • Regular tick at the same point in the stroke
  • Visible flat spot or material loss
  • Carriage sitting lower than it should
  • Noise persisting after thorough rail cleaning

Replace as a set

Wheels wear together and a new wheel alongside three worn ones sits at a slightly different height, which loads it unevenly and makes the carriage sit fractionally out of level.

A full set is not expensive and it restores the machine to its original glide, which a partial replacement does not.

Check the rails at the same time

A failed bearing usually means the wheel has been dragging rather than rolling, and dragging scores rails. Inspect the running surface before fitting new wheels — putting good wheels on a damaged rail wastes them.

If the rail is scored, find out whether it can be replaced. On better machines it can; on cheaper ones it often cannot, which is a useful thing to know before the next purchase.