What size of cylinders did the freight pacifics have and what was weight on drivers. Gary
Interesting question about a curious group of locomotives; but I only have part of the answer. From what I see in Edson's roster in R&LHS Railroad History No. 140, Spring 1979, many 4-6-2s in the 1031-1135 series were rebuilt with their 75 1/2 inch drivers reduced to 61 inches for local freight work. However, cylinders remained 25x26 and boiler pressure 215 lbs. so that tractive force jumped from 39,334 lbs. to 48,683 lbs. The weight on drivers is not given but total engine weight remained about the same so the factor of adhesion must have fallen substantailly. They must have been slippery and probably required some change in technique to operate satisfactorily.
The rebuilt engines were numbered 2030-2097. There was also 2098 which originally had 77 1/2 drivers, reduced to 61 inch, and 24x28 cylinders which remained the same. The IC must have been satisfied with the rebuilds since in 1948 it converted another Pacific with 27x30 cylinders and 215 lbs. pressure to use 61" drivers which raised tractive force to an exceptional 65,520 lbs. and reduced the factor of adhesion to a very low number. The Illinois Central "over-cylindered" many of its locomotives -- maybe a reader will explain the IC's thinking regarding its use of unusual combinations of driver size and cylinder size. My favorite IC rebuilds were the Atlantics that had drivers reduced from 80 inches to 63 1/2 for branch line freight service. In theory they had the starting tractive force of many a 2-8-2 but too little weight on drivers to use it.
The as built weight was 144,000 pounds and could run on 80 pound rail. Cutting 14 inches off the drivers would help in keeping the weight down to help in running on branchlines. Gary
Here is 2096:
http://donsdepot.donrossgroup.net/dr0502/ic2096.jpg
Gary - regarding your point about reducing the drivers of the Pacifics by 14 inches, (from 75 1/2" to 61") to reduce weight -- it didn't have that effect. Edson says the weight of the engines went from 249,900 lbs. to 242,150 ibs., a modest decrease of 3 1/2 tons. When the Atlantics had their drivers reduced the engine weight went up about 3 1/2 tons.
What is most surprising about these rebuilds is the factor of adhesion as I mentioned before. It is generally accepted that you need a factor of 4 or more for satisfactory adhesion, that is to keep the drivers from slipping. The as built tractive force of the Pacifics was 39,334 lbs. which means the engines must have had at least 160,000 lbs. on drivers. When rebuilt they produced 48,683 lbs. of tractive force which meant conventional design theory would call for roughly 200,000 lbs. on drivers or an axle load of over 65,000 lbs. --- that is more of an axle load than I think the Illinois Central could accept and therefore weight could not be increased in proportion to the increase in tractive force. However, it appears the Pacifics as rebuilt had a factor of adhesion of only around 3.3 which is exceptionally low. My question is, did these engines operate with a form of limited cut-off so that the starting tractive force was more in keeping with the roughly 80 tons they had on drivers? Why didn't the IC bush down the cylinders to decrease the tractive force --- so much tractive force was certainly not needed for the work assigned?
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