MO PAC? Pacific with Poppet Valves

Superheater · **Posted:** Thu Mar 27, 2003 12:31 am

I remember reading about a MO PAC (i think) 4-6-2 outfitted with rotary cam poppet valves. Engine was supposed to have a big boost in power @speed. If I recall correctly, the account said it developed the power of a 4-8-2 at higher speeds.

Anybody know whether the valves were kept on after trial?

Was the trial a success-just to little to late or did the technology of the time render it to maintenance intensive?

What was the engine and its disposition?

Appreciate any info, Thanks.

Superheater@rrmail.com

J.Nansen · **Posted:** Thu Mar 27, 2003 1:13 am

> I remember reading about a MO PAC (i think)
> 4-6-2 outfitted with rotary cam poppet
> valves. Engine was supposed to have a big
> boost in power @speed. If I recall
> correctly, the account said it developed the
> power of a 4-8-2 at higher speeds.

> Anybody know whether the valves were kept on
> after trial?

> Was the trial a success-just to little to
> late or did the technology of the time
> render it to maintenance intensive?

> What was the engine and its disposition?

> Appreciate any info, Thanks.
The Missouri Pacific did have a poppet valve 4-6-2.
Number 6100. All the dope on it can be found starting at page 187 of Joe Collias' book, "MoPac Power."
Apparently the locomotive turned in a pretty good record of itself.

j.nansen@worldnet.att.net

Hugh Odom · **Posted:** Thu Mar 27, 2003 7:24 am

"Trains" magazine also had an extensive article on the locomotive (in the late 1970's). It was originally built as a 3-cylinder by Alco, and was not considered successful. It was later rebuilt by the railroad (shortly before WWII I think) with 2 new cylinders with Franklin Type "A" oscillating cam (not rotary cam) poppet valves and other modifications.

Evidently, the engine was very successful and very well liked by crews, and retained the poppet valves until steam ended.

Good Steaming,
Hugh Odom

> The Missouri Pacific did have a poppet valve
> 4-6-2.
> Number 6100. All the dope on it can be found
> starting at page 187 of Joe Collias' book,
> "MoPac Power."
> Apparently the locomotive turned in a pretty
> good record of itself.

The Ultimate Steam Page
whodom@awod.com