classified steam repairs

[gacuster]

The new Kalmbach publication "In Search of Steam" mentions locomotives that have recently undergone "class 5 repairs."  What did this involve?  I assume that there were class 1-4 repairs as well and am wondering what those consisted of too.

[feltonhill]

The following list is based on AAR descriptions from 1924.  There are slight variations depending on the individual railroad

Class 1

New boiler or back end

Flues new or reset

Tires turned or new

General repairs to machinery and tender

Class 2

New firebox or one or more boiler shell courses new, or wrapper sheet new

Flues new or reset

Tires turned or new

General repairs to machinery and tender

Class 3

Flues new or reset (superheater flues may be excepted)

Necessary repairs to firebox and boiler

Tires turned or new

General repairs to machinery and tender

Class 4

Flues part or full set

Light repairs to boiler and firebox

Tires turned or new

Necessary repairs to machinery and tender

Class 5

Tires turned or new

Necessary repairs to boiler, machinery and tender including one or more pairs of refitted driver bearings

General Repairs to Machinery

Drivers removed

Tires turned or changed

Axle journals turned if necessary

All driving wheel boxes and rods overhauled and bearings refitted

Other repairs needed for the locomotive to perform a full term of service

[gacuster]

Thank you for the excellent answer.  No wonder railroads had such extensive shop facilities during the steam era!