The Steamboating Forum

Lopez Mike wrote:On a related issue, I have seen some slide valve steam engines where the port surface on the cylinder stood above the rest of the machined side of the cylinder such that the valve travelled slightly beyond the raised area. Thus as the port area wore down there would not develop an edge at the end of normal travel.

Which would also stop the valve edge for wearing off changing the timing.

We will not hold our breath waiting for my engine's timing to be set carefully enough for wear to be an issue.

Nice work Fred..

On the tug, each cylinder has a counterbore down the end of the ring travel. The piston actually peaks past the counterbore top and bottom to the edge of the rings. The counterbore is large enough to slip the ring compressor down in side for fitting the pistons. No chance to build a ridge. I think they did that to reduce head clearance and conserve steam. As the others have stated, I wouldn't be too concerned about cylinder ridging. That happened with old cars that had zillions of miles on them. I still have an inherited ridge reamer here that I used on the first engine I ever overhauled under the tutelage of my father. An old worn out 283 smallblock.

Not understanding an port edge wearing off on a slide/ D valve configuration. It is two mated planes, how is a valve port edge lost? Unless the valve is too small and is allowed to rock over the ports, all of them I've came in contact with have a very large surface area with heavy friction at higher steam pressures and why the piston valve, being a balanced valve is favored for higher efficiency. Though the old adage is "Slide valves wear in and piston valves wear out"

Mike, I would say you are in the vast majority with your engine timing myself included.

-Ron

Ron,
The end of the slide valve comes to a stop at pretty much the same place each time. The valve wears evenly but the cylinder surface only wears where the valve rides. I've seen them pocketed in an amazing depth. Mostly from poor lubrication, lack of any valve pressure balance, superheating and, in the case of coal burning locomotives, fine clinkers getting down from the exhaust nozzle when coasting. Because of the latter, most coal burners had coasting valves.
Non of these situations occur regularly in a small launch, of course.

Completed the cylinder and steam chest parts.

Used a drilling template for the cylinder heads made from a common chain drive sprocket. The sprocket hub (other side of the picture) was bushed to match the cylinder bore, inserted into the bore, and clamped in place. Pilot holes drilled with reasonable precision.

The number of sprocket teeth can be selected to give reasonable spacing of bolt holes, without use of an expensive indexing device. In this case I needed 16 equal spaces for 8 bolt holes, straddling casting centerline, so I used a 64 tooth sprocket. Bolt circle diameter is scribed onto the sprocket face while mounted in the lathe, then pilot holes drilled.

If anyone is building this engine, I will lend the drilling templates for the cylinder flanges and valve seat surfaces.

Completed cylinder casting, bored, counterbored, milled, and tapped

Machining the crank end cylinder head is a special case, as the mating to the cylinder bore and the crosshead bore must be accurately concentric.

In this case the ridges for both of these bores as well as flange faces could be made at a single chucking in the lathe, as the casting has an extension (for the piston rod packing gland) allowing the machining of both flange faces while maintaining perfect alignment. These ridges and flange faces need to be accurate so that the cylinder bore is alligned concentric and parallel to the crosshead bore.

Light cuts taken here, due to the small chucking diameter.

Completed cylinder and steam chest assembly. Steam into the steam chest 3/8 NPT on the side, with a port, 1/4 NPT on the cover, which might be used if a balanced valve is used.

I made drawings of this machine work if anyone needs them, let me know

Fred,

Looks good. What kind of lower end are you going with?

-Ron

Preliminary planning, a Vertical Inverted Engine, fairly typical for most launch engines, except the baseplate will be mounted above the crank main bearings. Marshall-Bremme valve gear of course. Still in the conceptual stage. I have the crank and connecting rod from an IC engine. Overall height will be alittle less than 20 inches.

I plan to make the crosshead and support columns as a weldment (additive manufacturing is the "new" term for this), rather than a casting. With proper stress relief that assembly will work fine, and look like a casting. The rest of the engine will be fabricated similar to the methods used for the sidewheeler walking beam engine.