[David Fletcher]

Chaps,
For what its worth, typically where Walschaerts valve gear is applied to piston valves, the eccentric will face forward, or lead the main rod crank. When applied to slide valves, the eccentric faces aft. Reason is that the designers intended to the Johnson bar and reverse links to funtion identially regardless of whether piston or slide valves were used so they simply changed the location of the eccentric relative to the main rod.

Piston valves typically have Inside admission and exhause to the outside, while slide valves are the reverse...thats why the valve travel work in opposition in both valve types.

Piston valves became popular as boiler pressures increased and super heaters started to be used, where slide valves performed poorly.

Many Mallets have piston valves on the rear engine and slide valves on the forward engine, becuase slide valves can handle the low pressure steam for the front cylinder, and thus the rear engine has the eccentric facing forward, and the front engine has the eccentric facing rearward.

On the Bachmann model, all chassis units have piston valves, so in principle the eccentrics should all face forward..., I've not looked at the photos, other than have a nice side view of the 110 with all eccentrics facing forward (as seen from one side), as are some of those drawings and sketches around which would make sense. There are some Mallets with piston valves to both chassis, with the eccentrics still facing in opposite direction - you'll notice on these engines, the rear engine's radius rod is lifted from behing the reverse link, whille the front chassis has the radius rod lifted fore of the revese link...in forward operation,..when the Johnson bar is pushed forward, this lowers the forward radis rod, but raises the rear one! Thus the engine still goes in forward motion, despite the radius rod on the rear chassis being at top of reverse link, while forward chassis valve rod has the radius rod at bottom of reverse link. With pneumatic actuators working some of these lifting rods, I have no doubt that the same engine would have had its eccentrics changed over time depending on the set up of the actuators...confused..it all make sense when you check out the photos!

I'd look to see if the model works best with the eccentrics all forward. Also, if the mounting of the eccentric was like the K-27, and could face forward or aft almost equal distances, the actual eccentric travel about the hub should be idential regardless of which way the eccentric faces, and shouldn't bind up like Dave shows. How are those crank pins fixed I wonder...maybe the crank pin is not set in the right position causing the eccentric travel about the axle to be too wide..which will damage rods regardless of which way the eccentric faces.

Darn good review Dave.
I'll wait till I see one in person to decide whether to buy. I'm selling my K-27, dont run it enough!

Ah just found some shots on the internet:
Side view, eccentrics lead main rod on both engine units:

http://loggingmallets.railfan.net/list/wt110a/weyer110ameh.jpg

sketch of the 110 - cant tell if this is original baldwin drawing or some later thing.
http://www.1880train.com/images/locomotive110b.jpg

Also looking at those Bachmann photos and video, the wacky motion with the eccentric rod seems to me to be due to the length of the tab on the end of the reverse links (expansion links for our UK friends) to be about half the length it should be, and slightly iin the wrong angle..but she's not 110, or anyhing else like her, but something Baldwin never got round to detailing, so who's to worry.
David.

 

[David Fletcher]

Matt,
I cant open what ever that is you're referring to, but YES Sorry I got it all backwards as soon as you raised it! Mixed up in my head between the two systems - Piston valve addmission is centre, slide valve is side. swap what I just said, bottom line, both systems are opposite, so the eccentrics will be opposite if the radius rods are to set the same way on both chassis'.

I could easily concieve how an engine like this could have 3 eccentrics facing one way, and only one facing the other, it would entirely depend on which way the cams pivoted relative to the lifting rods...dono why you would, but yes can be done. Its possible....and I'm guessing here, but the actuator for the valve gear is under the engineer's side tank, just in front of the cab. It pushes and pulls the reversing rod down one side of the loco to the lifting rods via some pivoting 'L' shaped cams...you can see them there on the model...when all the cams rock in the same direction with the valve change, then the eccentrics will always face the same way relative to main rod (on an all piston valve loco), but as seen in the photos, when one set of cams rocks down (lowering the radius rod), while the rear set rocks upward , raising the radius rod, then in order for both engine units to run in the same direction, the eccentric on both engine units will be opposite. Now on this crazy 3 matching, 1 different thing, maybe only one side has the cams rocking in opposite directions due to some space constraint where the actualtor takes up space where the cam would otherwise rock...this would mean the radius rod on one side of the loco lowers, while on the opposite side of the same chassis its lifted to the exact same amount, and the eccentric on that both sides would need to face in opposite directions. I cant believe someone would engineer that, but I dont know modern locos that well, who knows...check the photos I guess to see if the radius rods on both side of the loco lowered or lifted the same on all sides or not.

The one way to really know what should happen with this model, is to look at the connection of the lifting rods to the radius rods on the real engine, and see how that lifting rod is connected to that pivoting 'L' shaped cam. If you can see that the cams can pivot in the exact same way on both chassis, on both sides of the loco, then all the eccentrics should face the same way (forward of the main rod crank). If the cam look like they would pivot in opposite directions on the two chassis relative to each other when the Johnsonbar is moved forward etc, then reverse the eccentrics on one chassis - have the forward chassis with eccentrics facing forward, and the rear chassis eccentrics facing aft, which seems to be visible on several of those WA Mallets I can see. If you can check some photos of the real locos in motion (ie with radius rod out of neutral), you will see the radius rod on the front chassis down, and the radius rod on the rear chassis up...if you could see both sides of the loco from the same period in motion, see if the same condition is on both sides of the loco, then you'll know whether a 3-1 thing was done.

I'd just set the eccentrics to make sense with the lifting rods on this model and you'll be logical.

David.

 

[David Fletcher]

Chaps, check the video of the preseved 110 at the Black Hiills (on the 20.3 site), all radius rods on both sides facing down in forward and up in reverse. All eccentrics on both sides of the loco lead the main rod crank (eccentrics face forward in all cases). Go with that on your model. Historical photos do indicate locos of this type do have eccentics on the rear chassis facing aft, and radius rods opposing. Here is a photo example:
http://loggingmallets.railfan.net/list/bd9/rayon9meh.jpg
Note how the radius rod on the rear chassis is at top of reverse link, while forward chassis has the radius rod bottom of reverse link. The only way this engine will run in one direction is for the rear chassis eccentric to face aft and the forward chassis eccentric facing forward, which is exactly the case on this loco. The web site has the same loco photographed the year before from the other side, and its identical in its set up. No 3 -1 thing:
http://loggingmallets.railfan.net/list/bd9/wing-rayon9.jpg


Since this model is based on 110 to some amount, I think the 3 eccentrics facing one way and only 1 in the other on the Bachmann model is a mistake, like the K-27s not being consistant in this regard. It shouldn't damage the valve gear out of the box, so long as the eccentric travel of the aft facing eccentric doesn't move a circle of wider travel than the other 3 eccentrics, causing the reverse link to rock too far back and both and cause that bind in TOC's photo.
Set up your eccentrics on the 3rd axle on both chassis like this photo:
http://loggingmallets.railfan.net/list/wt110a/weyer110ameh.jpg
With the all eccentrics facing forward when the cranks are at bottom, thats how the 110 is preserved today.
David.