Q. 36. -Does this motion of the engine have an equal disturbing effect on the valve's motion with the Walschaert gear?

A. No, it has no effect, unless the connection of eccentric rod to link foot is placed at too high a point above the centre line of the axle.

Q. 37. When the crosshead is at the exact centre of its travel, main-pin on the upper or lower working quarter, reverse lever in centre notch, and the combination lever in a plumb vertical position, at what point in its travel should the valve be standing?

A. The valve at this time should be perfectly central on its seat, with both admission ports covered. Q. 38. What is meant by the above expression of the main-pin being on the "working quarter"?

A.-When the main-pin is on the actual quarter— either the upper or lower-it is on a perpendicular line through the centre of the axle, but the piston will not be in the exact centre of the cylinder, owing to the angularity of the main rod. On the other hand, if the piston is at the true centre of the cylinder—as was supposed in the foregoing question—the main-pin will be a slight distance away from the perpendicular line through the centre of the wheel, or axle, but it is now on the working quarter because, technically, it has half completed a single stroke; if the back end of the main rod should now be disconnected from the

main-pin and dropped, or raised, as the case demands, until it was on a horizontal line, the opening for the main-pin in the stub-end of the main rod would centre, exactly, over the centre of the wheel hub, proving that it was half-way in its stroke. The longer the main rod the less its angularity and the lesser will be the difference between the actual and the working quarterpositions of the main-pin.

Q. 39. The engine standing with piston at the true centre of the cylinder on one side and the reverse lever in the middle notch of the quadrant, suppose that the valve was not exactly centred-opening the throttle would cause steam to blow from one of the cylinder cocks on that side of the engine: What could be the cause, and how remedy it?

A. First, be sure that the reverse lever is in the middle notch; a mistake may have been made in laying out the notches of the quadrant, or in setting it up; when the link-block pin and the link-fulcrum pin are centred together the reverse lever is in the proper middle notch, and when they are so situated and the valve is not covering the admission ports completely with piston in exact centre of the cylinder, undoubtedly the link bearer, which is attached, commonly, to the guides, varies a little in its position, either fore or aft, and should be moved enough to correct the error; or the valve-stem can be lengthened or shortened, but as

this induces other minor errors the other method would be preferable.

Q. 40. Would not moving the position of the fulcrum that carries the link produce other error in shifting the distance between it and the eccentric?

A.-Re-setting the link fulcrum might correct the whole motion, if it had been set up untrue; but if correcting the position of the link fulcrum should cause the error suggested, that, again, can be corrected. by adjusting the length of the eccentric rod. Here is a fundamental point to remember: The gear from the link forward, inclusive, is permanently set up, all motion bearers being in rigid attachment to the guides. Back of the link, however, there may be changes in distances due to wear and consequent lost motion, and for that reason the eccentric rod, alone, may be lengthened or shortened as may be found necessary.

Q. 41. On the big, modern engines that are being equipped with the Walschaert valve gear there does not seem to be any convenient way of changing the length of the eccentric rod except in the adjustment of the bearings at its back end; how, then, could the length be altered as advised?

A.-Outside of the method just referred to, as stated before, it is a "back shop" job to alter the length of the eccentric rod, and there is where it should be done. The earlier built engines, with much lighter rods, and

foreign locomotives of the present date, had, and have, adjustable eccentric rods. In Fig. 10, Wm. Mason's improved design of the Walschaert gear, the eccentric rod is shown to have adjusting nuts near the connection to the link foot.

Q. 42. Then, if the eccentric rod is the only part of the Walschaert valve gear that can be changed outside of the machine shop and the only part that should be altered at any time in the shop, this motion is not likely to be tampered with, nor to get "out of square"?

· A.-That is right. The Walschaert valve gear will not wear away in its bearing parts enough to make it necessary to have adjusting devices.

Q. 43. Explain when it will be necessary to correct the length of the eccentric rod.

A.-Set the engine with the main crank-pin on the forward dead centre on one side, and have the reverse lever moved from the go-ahead corner notch up toward the centre of the quadrant; while the link-block is rising, if the valve-stem is pushed forward slightly the eccentric rod should be lengthened; but if the valve-stem should be drawn backward by the rise of the link-block the eccentric rod needs to be shortened. In either case make but slight changes in the length of the rod, and keep on testing until hooking up the lever to the centre has no effect on the valve-stem nor

radius rod. Then test, and alter if necessary, the other side in the same way, but with the main pin on the back dead centre.

Q. 44. The numerous engravings of locomotives equipped with the Walschaert valve gear show that the link bracket is invariably attached to the guidebearer, or yoke, and the slide for the valve-stem is mounted on the upper guide-bar: Does this just happen so, and as a matter of convenience, or is there a reason why the main supports of the Walschaert gear should always be so contained?

A. It is very important that the trunnion upon. which the link oscillates should be fixed at an unvarying distance from the cylinder, and for assurance that the distance will be permanently maintained, the link bracket should be rigidly fastened to the guides; and as the valve-stem slide supports the combination lever and front end of the radius rod, it represents a point where no variation in the motion is permissible, and it, too, is secured fixedly to the guides.

A type of heavy-freight engine has recently been built on which it would have been inconvenient to hang the link as recommended, and a large, hollow, cast-steel bracket was laid across, joining the bars of the engine frame on both sides just back of the guideyoke, to act both as a frame binder and brace and a carrier for the link bracket. With one class of this