Disparaged Y class engines!

NW Mailing List nw-mailing-list at nwhs.org
Wed Jun 26 08:39:07 EDT 2013

In a discussion of Bigboys and Challengers I responded:

With all the discussion about articulated's, lemme drop my 2 cents......

BB and Challengers were "OK" designs but had different parts front to back engines, so maintenance was more costly(parts availability) N&W took the USRA 2-8-8-2 and improved the exhaust porting in their Y5 series, which allowed them to get out to 55-60 mph, while still being able to start in simple, providing 152K tractive effort. while not "High Speed" they were optimzed to the grades and curve on the N&W. This was NOT done with the C&O H8's. They also developed the "A" class 2-6-6-4 earlier than the C&O H8's and even though they had slightly larger drivers (67" vs 70") the increased bioler pressure gave them a slightly higher TE than the H8's. Factor of adhesion was higher for the H8's due to their higher axle loading and smaller drivers (4.10 vs 3.78). By 1952, N&W had added 16 tons of lead onto the front engine frame to combat slipping due to better valve timing and the addition of the booster valve. Those Y6b's could generate 170K lbs TE at 6 mph. They were still able to get out to about 60mph on the flatter areas. The "A" class could get up to 100mph on the flatlands, like the "J" class passenger loco's. C&O's H8's might have been improved by increasing boiler pressure to 300lbs but they were already using them wrong for most of their service life as drag locos. It wasn't until 1948 and later that they realized the H8's could pull enormous trains at 65 mph.


The N&W Mallets pounded the rails at speeds above 40 mph, and so they were restricted by the management to slower drag speeds. Fortunately for alcon, that worked out the best. Any time you have massive reciprocating and eccentric weights circling small drivers, which the Y's had, where there is so little counterbalancing mass able to be applied effectively in the smaller circumference, you get high dynamic loading on the rails which literally pulverizes the ballast (not a good thing), splits ties, and bends the rails...also not good things.

The I RESPONDED...............

Not true. The only engine that had problems with counter balancing was the K3 4-8-2's, which had their main siderod connected to driver #3 instead of #2 for more starting TE. They pounded the rails as driver #3 hopped above 38mph and it was those engines that were restricted to 35mph. The Y class drag engines were mostly used in areas where 20-35 mph was the speed limit. They only time they went faster is when working with an A class engine.

The Y5's and Y6's had 58" drivers and more counter weight, but it was the Y2 - Y4 series that were unable to get past 40mph due to the bottleneck in their front engine exhaust porting/piping.


We can disagree. I believe the Y6's had 57" drivers. I have read many threads on the subject of articulated steamers around the www, and the consensus is that the drag engines were best at drag speeds for a number of reasons, including dynamic augment due to their counterbalancing problems associated with the longer cranks relative to their smaller tire diameters and their associated wheel mass, the hunting of the hinged front end engine holding the massive LP cylinders, but also that they simply ran out of lungs/steam at speeds above 45 mph or so with the reverser set forward and the throttle pulled well back.

The Y's and A's could accompany each other down grades at the end of a pushing shift at speed where horsepower was not being applied, but when it came to speeds above 45 mph, that's what the company designed and built the A Class to do.

Are any of his responses true?
Did the rails get pounded by the Y class engines?
Did N&W management restrict their speeds because of this?

Mark Lindsey
Stuck in the 1930's

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