S.P. 4-8-0's

[UP 829]

I understand S.P. had a small group of locos with this unusual wheel arrangement. Anyone know more about them, in particular why the 4 wheel lead truck? The drivers don't appear overly large in the picture I've run across. Were they built for a specific use or branch line? I'm guessing they may have been compounds originally, but compound 2-8-0's were quite common.

[jimrice4449]

They had a fair sized bunch of them, especially in view of the relative rarity of the wheel arrangement (N&W notwithstanding).  I don't have any SP roster info available but I believe they were built as simple for branch line use in highly curvaceous areas.   That guess is borne out by the fact that most of them wound up in Oregon.

[KCSfan]

I am not familiar with the SP 4-8-0's but the 4 leading wheels suggest they were at least originally intended for passenger service. Perhaps SF Bay area commuter or mainline passenger service in mountanious areas before the advent of 4-8-2's and Northerns.

IIRC the N&W 4-8-0's, at least in the later steam years, were used mainly on branch line mixed trains. Despite their overall slow schedules, these mixed trains often made moderately high speed dashes between towns and the 4 leading wheels served to guide the engine around the many curves of the N&W's Appalachian branches at the higher speeds. This makes me believe that Jim may very well be correct about the SP using these engines in branch line service.

Mark 

[oldline1]

Mark,

What does "IIRC" mean?

Thanks,

Roger

[KCSfan]

Mark,

What does "IIRC" mean?

Thanks,

Roger

 

IIRC = If I Remember Correctly 

Mark

[oldline1]

DUH!!! That one had me stumped!

Thanks,

Roger

[AltonFan]

Most of these engines were originally built as compound engines, in which steam was ehausted from one cylinder into another.  This was done to obtain greater thermal effeiciency.  The four-wheel pilot was used in this instance to support the additional machinery in the cylinder area.  When these engines were rebuilt as simple engines, they retained their four-wheel pilots.

It should be pointed out that most 4-8-0s were built in the last years of the 19th and the earliest years of the 20th centuries, before superheating was invented. 

Twelve-wheelers demonstrate one of the exceptions to the generalization that "four-wheel pilot = passenger train".  Most were designed as heavy freight engines, and had typically had drive wheels smaller than 60" (50"-56" was more typical), which limited speed.  (OTOH, one of the last 4-8-0s, built for the Mexican National Railways in the 1930s, was essentially a 4-6-2 with a drive wheel substituting for the trailing truck.)

Another reason a railroad might use a four-wheel pilot on a freight locomotive is to allow lighter axel loadings on the drive wheels in areas with poor track.

For some reason, I've always liked the looks of 4-8-0s.

[espeefoamer]

Southern Pacific used their 4-8-0s mostly on branch lines in Oregon.