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I have one of these coming, but it's not here yet. Anyone else in the MLS community have one delivered (or ordered?) I too will be interested to see how they chalk up to the one in the review.

The photos in the review, particuarly the comparison photos to the LGB unit show it to be a bit larger than I'd thought it would be after seeing some of the photos on the Bachmann site, which to me is a good thing.

Matthew (OV)
 

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David,

I was following your explanation, and really enjoying it, but had a question ....

The review on the Durango Dan site references this: http://www.google.com/books?id=TKV-AAAAMAAJ&printsec=frontcover#PPA103,M1 which made a really good read on Walshert's Valve gear .... and its explanation of "outside" and "inside" admission is exactly backwards from yours. (Page 102 and 103) ... so I confess myself a bit confused.

Also, both the model in the review and in the bachmann Movie that Stan mentions have three cranks one way and one the other .... and he says they may ALL be like this. Is there an example of a prototype locomotive set up this way that you've heard of? If so, what was the reason?

Matthew (OV)
 

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A mark of a good review is that it presents the reader with enough information about the subject being reviewed that the reader can draw his own conclusions about what is being reviewed. That, in a nutshell, is the difference between:

"To me they appear to be working properly"

and

“As delivered, three eccentrics pointed one direction, one pointed the other. Experimentation has shown that as delivered the front engine eccentrics need to be mounted forward of the axle, with rods down. If not, it is easy to have one reverse link “knee over” and lock the valve gear. The results could be disastrous. One set of valve gear on the locomotive reviewed was discovered locked in this manner when it was removed from the box. The rear engine eccentrics needs to be mounted aft of the axle (with rods down), to keep the reverse link from hitting the stops. The valve gear is NOT adjustable, the valve rod does not move in and out of the valve body.”

One of those statements containes useful, factual, information, that might help me come up with a way to make a $600.00 locomotive out of a $600.00 mistake. If it does, the folks in Philadelphia will have the advisor to the 1:20.me review to thank for the fact that I'm not leading the torch and pitchfork crowd when it comes to Spectrum locomotives.

As a community, when the facts point in a less than fantastic direction, we need to stop blaming the messenger, and recognize the difference between product review, and product promotion. And for those who feel compelled to "defend" the company or its various personalities, a critical review that recognizes problems is NOT negative. As pointed out above, at least with an identified problem, I can work on a solution, and maybe make something good of it, whereas if the problem is denied or quashed, and questions go deflected, unanswered, spun, or ridiculed, I am dead in the water with no way to fix the problem (which, for all of the shouting, will still exist.)

Matthew (OV)
 

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Cale said that. It's the quote problem again... Cale didn't go down far enough to separate the first line of his post from the next, which was double spaced and did make it out of the box. Probably why he tried twice.

(and no, I'm not being critical of anyone at Mylargescale by explaining this ... I'm trying to offer a solution to a problem. See the diffrence?)
 

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Locomotives with piston valves typically have the eccentrics positioned as in the first of your two K-27 links (the one on top) above.

The link on the bottom shows the other choice, which you'd see with slide valves.

On the Mallet, since it has piston valves, you'd expect the eccentrics to match the top photo.... all four of them.

Now, as David Fletcher pointed out, there are exceptions to this rule ... most involving the positioning of the gear that makes the sliding part of the link block move up and down. But the Mallet, at least as the model is built, is not one of those exceptions, since it matches the construction of Weyerhauser #110 very closely (and the 1:20.me review illustrates that.... so I'm referring to that as a source here.... just in case folks still want to argue about copyright!)

The point is, when the link block is moved down, the eccentric moves in synch with the radius rod, and the locomotive moves forward. When the link block is raised, the link acts as a rocker arm, and reverses the action of the eccentric rod, causing the radius rod to move exactly opposite from the eccentric rod, and the locomotive moves in reverse. If your eccentric rods are backwards, it'll all still work, except that you'll have to move the reversing lever backwards to go forwards and vice versa. If everything else matches, and you have one leading and one trailing, one part of your locomotive will be trying to move forward, and the other will be trying to move backward.... which doesn't work on a locomotive that actually uses its pistons and valve gear to generate power and motion.

Does it matter in an electric model locomotive? Probably not. There are Aristocraft locomotives from a while back that everyone loves a lot that have all that hardware cast in plastic. Old Lionel stuff often doesn't even have all the pieces... and they've been favorites of people for a long time. But, if I'm going to spend a lot of money on a finely detailed model, I'd like it to be right. Notice that with the K-27 above, one of those is right, and the other ... is not. Which would you select, given the choice?

Now ... there is a separate issue involving the binding of valve gear components based on their position. As far as I know, there has not been any published information on what the source of the problem is, or how to best go about addressing it, but there have been pictures posted of valve gear on the Mallet that is, to say the least, "out of whack." I have not heard of any such issue on the K-27, beyond needing to have the eccentrics reversed, which mine have been. So I'll be watching to see when my Mallet arrives, because I want it to run well, and because, well, it matters to me that the valve gear is arranged correctly.

To those to whom it does not matter ... good health, and happy running.

Matthew (OV)
 

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Uh, Semper.... I was with you right up to the end there.

On many Mallets, the front, low pressure engine had slide valves (with the squarish valve chests you describe) while the rear high pressure cylinders had piston valves. On those locomotives, what you outline above is exactly right.

On later models, though, all four cylinders were equipped with piston valves, both the large low pressure cylinders up front, and the smaller high pressure cylinders in the rear. On these engines, all four cranks would "Lag" or follow the eccentric, as they're all valves of the same type.

The Bachmann 2-6-6-2 has piston valves on all four cylinders.

(and, for sake of completeness, in a locomotive with four sets of slide valves, all four cranks would "lead.")

Matthew (OV)
 
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