Medco 4 Restoration  -- Boiler Work

The long, slow process of rebuilding a locomotive boiler


Last, but certainly not least, we come to the boiler: by far the largest component of a steam locomotive. Over the course of the last year it has received the lion's share of attention and money and will continue to be the focus of activity for at least another year.  Jerry Hellinga has assumed the monumental task of overseeing the rebuilding of this large hunk of steel and will have spent thousands of unpaid hours of his own time on it before a fire can be lit in Medco 4's firebox once again.

Click on the pictures below for full size images.

Firebox end of boiler on blocks      Resting on oak blocks a few yards from the frame, the boiler sits naked, striped of insulation, lagging, gauges, valves, piping and accessories.  This is the firebox end and the part where most of our problems had occurred. 
     Oil from the tender flows to a nozzle at the front of the firebox and is atomized by steam as it squirts into the firebox and ignites.  The oval hole in the left of this picture is the firebox door opening.  Just above this door is the crown sheet; the steel plate that separates the boiler above from the fiery inferno below.  Portions of the boiler also wrap around all four sides of the firebox effectively jacketing the combustion chamber with water under great pressure.  The fire pan is attached to the bottom of the firebox, the only part not surrounded by the boiler. 
     Now, imagine the task of keeping all these layers of curved and formed steel intact under 175 psi pressure and with a 1200 degree fire blasting away in the firebox and through the tubes.  Hundreds of stay bolts hold the inner and outer boiler plates together.   Most of the boiler material is 75 years old, has been patched and has never been so thoroughly inspected since it was new.  Corrosion has occurred; thousands of heat/cold cycles have developed cracks and warps.  The challenge is to find the weak spots and repair them.
     The gray spots in this and other photos mark where ultra sound readings have been taken of boiler plate thickness.  This is the first step in locating areas that need attention.
Scaling the boiler      The barrel portion of the boiler, pictured here looking through the flue sheet from the smokebox end, was in pretty good shape and needed no serious repair.  However, before a full exam could be performed, years of accumulated scale had to be removed.  In this picture Jim Dougall is wadded up running a needle chipper to break loose these deposits.  Loud, dusty and monotonous describe this job, but it's got to be done.
     If you'd been wondering where the background for these pages came from, it should be obvious now.  Flues (through small holes) and superheater tubes (through large holes) run through the boiler barrel and are secured at the smokebox end through this flue sheet. 
Emerging from boiler through steam dome Larry Tuttle exits through the top of the steam dome (the only way in and out) after a couple hours chipping scale.  The job's really not too bad once you get into it, but it's certainly not for the claustrophobic.
View from inside  the firebox Back in the firebox end, some of the boiler sheet has been cut away below the door opening.  The rust colored plate forms the firebox side of the boiler while the exposed grayer plate at the back of the lower firebox, with burned off stay bolts protruding, is the outside of the boiler. 

The half dollar size nubs in this and other boiler pictures are stay bolt ends that have been peened over.  In order to remove any plate, these must be burned away.

Deterioraton in boiler plate This is the sheet that was cut out in the view above.  Jerry is pointing to deterioration  that has occurred where the plate was attached to the mud ring at the bottom of the boiler.
Cut out boiler section with mud ring exposed Compare this picture with the one at the top of the page and you can see where some of the outer plate has been removed and the mud ring is exposed.  The C-clamp on the mud ring is helping to hold in a new piece of boiler plate.
Replacement boiler plates in place, welded This is the inside view of the same corner pictured above.  Note the new corner plate clamped in place and awaiting the welder.  Also, note the mud ring at the bottom right.  The deteriorated plate Jerry was pointing to came from this corner. 

To the left of the clamps and new plate is an irregular section of new plate already welded in place.  Suffice it to say, certified welders performing full penetration welding is a must with this 3/8" thick steel.  Other sheets of the boiler are 1/2", 5/8" and 11/16" thick.

Grinding staybolt holes Some of the stay bolt holes were damaged in burning out the stay bolts and others were oversized from previous repairs.  To fix this, the holes must be partially filled back in, rebored, reamed and retapped.  And before this can be done, the holes must be ground out to remove all threads and torch burns so the new material can be properly welded in place.  Here Larry is using a die grinder to grind these stay bolt holes.  He also found a couple cracks in the boiler plate in this area which now must also be repaired by welding.
View through firebox door A peek out from inside the firebox finds Jerry (right) taking a well deserved break and chatting with Chapter members Jim Dougall (left) and Rick Aubin (center). 
SOC/NRHS Home Page Medco 4 Page Mecdo 4 Disassembled Page
All images and text Copyright 1999, 2000 by the Southern Oregon Chapter, National Railway Historical Society.

This consist created by Larry Tuttle and  last yarded on April 9, 2000