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Coal Firing Aster's Big Boy

by Yves Guillaume

I have been coal firing my UPS BIG BOY 4002 (first series manufactured in 1981).  However, to anyone who is desirous of following in my footsteps I offer the following advice.   

 (1) Modify the blower jets. For gas firing the arrangement is fine, but the jets are too large for coal firing. Furthermore, the twin blower jet fitting in the smoke box is attached to the steam line exiting from the boiler front end by a rather flimsy arrangement using an M2 screw (I believe). All that has been changed on mine.  

(2) Still in the smoke box. There will be need to seal the space between the copper boiler itself and the boiler casing. When I did my conversion, I could not for the love of Mike understand why I was not getting adequate vacuum (drafting), only to realize that that space was the problem. 

(3) The two ash pans have damper openings front and back. I blanked off the front openings on both. The ash pan to the front of the firebox has the front damper opening located very close to the eccentric sheave and cam for the axle driven water pump. No need to tell you why that opening should be blanked off. 

(4) The fire grate provided in the Aster Big Boy kit (4002 series) was a ‘folding’ type. After one steam up session, the grate became badly distorted and I had to condemn it and have one made (in one piece) and placed permanently in the firebox. A couple of years ago Hans Huwyler (Aster Hobby USA) had some made (a 2 piece arrangement) which has so far held up beautifully. That would be the way to go. 

(5) Don’t let the apparent ‘shallow’ grate put anyone off coal firing Big Boy.  

In conclusion, therefore, one can successfully coal fire Big Boy. I usually get a ten to fifteen minute run at the very least before re-stoking.


A view from the boiler backhead. Fire grate visible. No water added yet !

Underside of Big Boy to show where front damper opening is sealed off. Fire grate is visible from damper opening facing the rear. Same was done to ashpan at back (above rear bogie).

A view of the smoke box – top half removed.

Blower jets and blast pipes – modified as shown.

Preparing for a run.

Charcoal soaked in mineral spirits being shovelled in. About sixteen shovelfuls are added.

Extractor fan is on and the fire is lit.

I got rid of one water line. One less clack valve to worry about. Refer back to pictures 1 and 6 to see where one is blanked off.

About ready to move off. You can see the fire glow from the two damper openings (at the rear of each ash pan).

Topping up before departure. Photographer kept me back !

Prior to opening the throttle, I am opening the water by-pass line to avoid the rear drivers “snatching” at the start-up.

Big Boy let loose !

Southern Steam Trains thanks Yves Guillaume for his generosity, expertise and supportive friendship within the Gauge 1 live steam community.  This article offers information and inspiration to those embracing the art of coal firing in small scale live steam locomotive.




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