Re-facing Slide Valve & Ports

[Builder01]

Harold, okay, sounds like silicon carbide would be the abrasive of choice. Thank you for the answer to my original question!

Maybe I will replace the slide valves with cast iron before I scrap the cylinders? It should also be possible to just replace the sliding surfaces with cast iron.

Meanwhile, I will reface the port faces and slide valves with silicon carbide abrasive. I am also going to see if I can get two clicks out of my lubricator instead of the one that it is presently set to do.

David

[Builder01]

Should I scrap all of my bronze bushings and replace them with cast iron? Have I set myself up for disaster on all of my rods?

David

[Bill Shields]

no no no no....bronze bushings are just fine. Don't panic here..just think things through.

changing the sliding surfaces with cast iron is a real undertaking. It is best if you design things that way from the get-go.

these cylinders are a silver soldered assembly of steel and phosphor bronze (on the top) with cast-iron sleeves for the pistons.

Silicon carbide is the best for what you are doing, but if you have something else available, I would not panic. Just use a good coating of light weight oil along with the sheet abrasive, work in an figure '8' and go slow...you will be ok.

making the valves from cast iron may not be a bad choice (actually it is a good choice), but if you are in a time crunch, I would just get the surfaces flat and call it a day. Even if you make new valves, you need to get the surfaces flat, so you will be saving no time.

Scratches in the surface can be caused by all sorts of things other than lack of lubricant...not the least of which can include contaminants in the steam.

One thing that people don't think about is junk from the smokebox, getting down into the blast pipe while 'cleaning up' at the end of the day. Once the crud is in there, all you need to do is push the loco BACK and FORTH a few times, and you have a good suction coming IN through the blast pipe, carrying everything with it, straight into the steam chests...

Not to feed fuel to the fire, but I have a small loco that runs completely without lubrication with brass on bronze and has for darn near 20 years...as do (almost) all the Raritans since day one -> designed with brass valves on (red) brass cylinders (or is it brass on brass...Joe T can answer that without looking in the book.)???

if you think the problem is because of no lube, then it might be best to spend your time fixing the lubricator..especially if you are going to use iron anything...since it will pit if left wet and standing unless it is doused in oil when you are finished running (but may be done with an oilcan through a plug).

one thing that I WOULD check is if there is a 'cut way' on the cylinder surface at the end of the valve stroke. Not having this can allow the cylinders to wear 'dished', and introduce excess wear. No matter what you do, if you are going to have the cylinders OFF and there are no 'grooves' at the end of the valve stroke, I would take care of this BEFORE you clean up the surface.

No, I have not yet cut the cut-away relief in the example cylinders above..but will be doing so shortly.

if you cannot visualize what I am describing, attached is a photo of a 55 year old loco that has never had the valves / cylinder surface touched.

YES it is cast iron on bronze...but you will see that the CI is beginning to pit and will not be long before it requires a resurface.

[Builder01]

Bill, thanks. It was just that some of the posts sounded like that bronze is not suitable for a bearing surface. (So I was slightly kidding about tossing out my bronze rod bushings).

The fact that you have gotten 20 years of a brass on bronze surface is quite telling. Folks sometimes forget that many things, that are not appropriate in full size, can work fine for a miniature.

I would like to get things working properly with the materials at hand before changing anything to iron. I don't look forward to replacing bronze with iron and then making sure everything is lubed at the end of a run, such that nothing pits or rusts. This is supposed to be one of the benefits of bronze over iron for cylinders and valves.

You are the first to mention the "cut away" or "relief" at the end of the valve travel. I made these cylinders and there is no relief at the end as the drawing did not show this. I was wondering if I should add this. Sounds like you have a vote on adding this, I will do this as it's easy enough to do once the cylinders are off the frames. Yes, do it before refacing the cylinders.

A question about the relief groove is, where should the edge of it be? My club track is quite "hilly" and I always notch up after the first long grade. This means the end of the valve travel is not always to the max when notched up. Should the edge of the relief be a little shorter (distance wise) than where I might normally be notched up?

David

[Builder01]

Bill,

Your 1st and 2nd photos did not initially come though. I only saw the last photo. The first photos are pretty cool! I see what you have done, very nice! I see the common groove to connect the exhaust ports. Is this for a 3-1/2" gauge loco, or, smaller?

David

[Bill Shields]

thought you would ask this.

the 'inside edge' of the relief should be just under the overlapping edge of the valve with the valve gear in FULL TRAVEL.

basically the edge of the valve 'peeks over' the cliff created by the relief groove. What you DO NOT WANT is for the internal CUT-AWAY of the sliding valve to 'see' the edge of the groove...otherwise you will get a massive steam leak.

If you run 'hooked up', then you can consider cutting the grooves a bit closer to the ports...just be careful.

The 55 year old cylinders you see in the photo are dead flat and still seal like new.

I am (not) surprised you have not seen this, however if you look through any of the old design books (like Steam Locomotive Study Course), you will see this groove illustrated..not as a 'groove' but the valve / cylinder mating surface is 'up in the air' at the ends so that this 'relief' is really a cast in surface that is not machined to mate to the valve.

These grooves are not often seen in small live steamers (usually not seen in the design), but I can freely admit that over the years I have rebuilt several locos that did not have these grooves and the mating surfaces were no longer flat.

[Builder01]

Bill,

Okay, the position of the edge of the "groove", as you have described is exactly where I would have suspected it to be placed. I will place it so it is just under the edge of the slide valve when in the notched position. This will also work just fine for the full gear position. (I will certainly check to confirm this!) Yes, do not allow the slide valve to "connect" the inside of the steam chest to the exhaust port - that would be bad!!

David

[Bill Shields]

You have it.

In REALITY, if you can work it out, you want the 'leading edge' of the valve to ALWAYS be 'peeking over' the edge of the groove at all used cut-offs.

another picture....for others who may be just 'getting in the groove'....

[Bill Shields]

this should be obvious but....

before you cut the groove, be sure that you have all the 'slop' out of your valve gear....

[Dick_Morris]

On material selection - what is a good material to use for the steam and valve pistons when SAE 440 bronze bushings are used for cylinder liners? I thought it would be good to not use cast iron to stay away from any rust and pitting. Should stainless steel be avoided due to potential galling?

[Harold_V]

Stop and think WHY CAST IRON is used (or Meehanite if you are familiar with name) as opposed to Bronze.

Young's modulus of CI is almost 2X that of Bronze.
Coefficient of thermal expansion of Bronze is 2X that of CI

Excellent points, Bill.

Along with those qualities, cast iron is one of the easiest of all alloys to pour, according to pretty much everything I've read (no personal experience). It flows well, very unlike many of the copper alloys, which can be difficult to cast.

I suspect bronze/brass was used extensively at one point in time simply because it was far easier to melt than iron, and the cost of copper, then, was not substantially higher than iron. As an example, I recall paying about $18 for a 250 foot roll of 12-2 w/ground Romex (a long time ago, mind you).

A crucible furnace is more than adequate for those alloys, while iron is difficult to manage with a crucible furnace. That's due to the higher melting temperature of cast iron. It isn't common for iron to be melted that way, although it is done, especially by the home foundry. Typically with less than uniform results, however.

H

[Bill Shields]

bronze on bronze is a good combination for your pistons/valves.

the primary goal should be to not damage the bores of the pistons / cylinders.

are you using any type of metallic piston / valve rings? If you are, and they are CAST IRON, then perhaps cast iron also for the pistons / valve bodies could be considered.

stainless is bottom of my list list