1:20.Me 2-6-6-2 Review

Posted By Dwight Ennis on 01/17/2009 7:28 AM
With respect to Bachmann yanking that particular post, in all fairness to Bachmann, it could also be do to what in their eyes constitutes copyright infringement. Note Cale's post...

then Andre did post the review, almost in it's entirety asking the Bman to respond:
Bold mine

Andre' would probably have done better to quote a few sections and post a link to the entire review. Copyright infringement could also be just an excuse for yanking the post, but the "fair use" clause has severe restrictions on it now with the Digital Millennium Copyright Act, and lawsuits over copyright infringement are very much a reality now. And we all know there's no love lost between Bachmann and 1:20.me. hehehe




Good Eye Dwight! I was wondering if anyone caught that? Yes; a link or smaller bits and pieces or even mentions of speculated issues could have been posted...probably ignored, but posted none the less.

cale

Posted By lkydvl on 01/17/2009 8:47 AM
As to copyright, my thought was that since I was also noting where the material came from, it would not be an issue.



Andre`





Yeah me too, another reason I used the above quoted and bold text..oh well! We'll give you cool points for trying!

cale

Dwight and I met at the Train Shop in Santa Clara yesterday to do a bit of buying and snooping on the Mallet. They had four of the Mallets in stock on display shelves and the shop owner said he had test run all four and they ran very smoothly (there's a benefit of buying from your LHS). They were priced at $649...which is a good price from what I've seen. Some observations:

[*]On all four engines the eccentrics matched on the firemens side as far as rotational placement during assembly. [*]The eccentrics were installed such that they lagged the driver...opposite what the "consultant" on 1.20pointme had said was correct. Since this engine was never fabricated in real life, "correct" may be tough to establish. [*]We took one engine out of the display case, and the engineer's side matched the firemen's side...all eccentrics were installed in the lag position. [*]With it out of the display case, we were able to "unscientifically" test (mess with) the rear coupler arrangement that I have some concerns about. [*]It does indeed slide fore/aft as you move it to the side and apply load. [*]The springs that are on the coupler ONLY center it when there is no or very little load on the coupler shaft. [*]The last step on the coupler shaft IS the load bearing surface as I had surmised from looking at the photographs on 120pointme. [*]That coupler shaft bears agains a metal plate that spans the width of the cab. [*]Under load, when moving the coupler left of right, you can feel some small amount of sidewards resistance. It's a small amount and I doubt (there's a scientific term) that it is sufficient to cause a tender/follow car derailment. [*]Lubricating that rear metal plate would probably reduce the resistance to sideways motion...BUT [*]The lube will provide a place for dirt to collect while running as this area is very exposed [*]The centering spring area also is a place where dirt will collect...and that assembly has a small plate that runs in a channel with springs on each side...so some kind of lube is going to be needed anyway. [/list] [/list] [*]The cab swing is significant. We didn't ever put the engine on track while at the store, but we did position the motors as if it was on a curve...and IMHO, the center rear of the cab does extend beyond the outer rail in my estimation...so this weird coupler set up is vital. [*]Folks with tunnel portals on curves...and at the BEGINNING of a curve want to be careful here...more clearance might be required than usual. [*]Lastly....our most interesting find...the eccentrics on two K27s. There were two K27s...on shelves...one above the other. [/list] http://1stclass.mylargescale.com/mikereilley/Chat/K27%20lag.jpg

http://1stclass.mylargescale.com/mikereilley/Chat/K27%20lead.jpg

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)

Posted By Mike Reilley on 01/18/2009 10:21 AM
... snip
[*]The eccentrics were installed such that they lagged the driver...opposite what the "consultant" on 1.20pointme had said was correct. Since this engine was never fabricated in real life, "correct" may be tough to establish. [*]... [/list]


Actually "Correct" is relatively easy to establish.

Look at the Steam Chests of the engine in question. If it is squarish (flat top and sides) then it is probably a Slide Valve, if it is round (tubular), then it is probably a Piston Valve.

Slide Valves are Outside admission and Piston Valves are usually Inside admission.

With Outside admission the Eccentric Leads the Crank Pin, and with Inside admission the Eccentric Lags the Crank Pin.

THUS, if you look at an engine, if the Steam Chest is squarish then it is probably a Slide Valve with Outside admission and the Eccentric should Lead the crank pin

If the Steam Chest is round then it is probably a Piston Valve with Inside admission and the Eccentric should Lag the Crank Pin.


Mallets (or Malleys, as they were sometimes called, which is closer to the French pronunciation of the French inventor's name) are by definition two engine Compound locomotives where one engine (usually the rear engine afixed solidly to the frame) is High pressure, and the second one (the one that is hinged to the frame and is free to swing side to side to follow the curve of the track) is Low pressure (working of of the exhaust of the first engine).

THUS, with a Mallet, the rear engine's Eccentric should Lag the Crank Pin and the front engine's Eccentric should Lead the Crank Pin.

Round Steam Chest = Lags
Square Steam Chest = Leads

EASY!

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)

You (Matthew) are right, That is why I said to "look" at the engine to determine what kind of valve chest is on it.

Some Compound engines had the high and low pressure engines in the opposite positions.


I also used the words "probably" and "usually" because some engine designers didn't follow convention! That was rare, but did happen. Some tried Inside admission Slide Valves and some had Outside admission Piston Valves. The drawbacks to these situations were soon learned and the practice settled on what you find in "most" locomotives/engines.

Some engines were field modified, especially when the Piston Valve was invented, many Slide Valve engines were converted to Piston Valves with a sort of "retrofit kit" so they still had squarish steam chests, but internally they were Piston Valves. Some still had Outside admission and so followed the "rule", but others were switched to Inside admission and that cornfuzes the "rules".

Visual examination sometimes fails the "rule". This then leads to the only difficulty in determining what "should" be, especially if the model has no prototype... make up yer own story as to what is in the Steam Chests and stick to it! "Hey, this loco was an experimental one built for the Hawaii to Taiwan RR and had Slide Valves on one side and a combination of Poppet and Magic Valves on the other."

I feel stupid asking this, but . . . .

I have been trying tofollow this thread because I would like to have one of these engines someday but I don't understand somethings.

Are eccentrics and counterweights the same thing?

I have looked at the two links by Mike Reilly and I cannot see any difference.

So, maybe there should be a forum that deals with the basic terminology and construction of a steam engine.

All I know is I love to see them and watch them and smell the smoke and grease.

How they operate is a total mystery to me.

So if you don't mind, could someone take the time to describe exactly what it is we are talking about so an idiiot like me can understand it?

Thanks,

John