Stuart #4 Cylinder Port Core Issue

[comstock-friend]

The core used to cast the cylinder on my Stuart #4 does not allow the ports to be machined to the drawings.

This kit was purchased in London in the 1970’s; glad I didn’t have to explain this to current TSA or UK equivalent on my flight back to Los Angeles! Obviously I can’t return the Stuart casting.

Anyway, the exhaust port is supposed to be 0.250 inch and it is, but the lands between the exhaust port and the steam ports are supposed to be 0.125 inch and they are less than 0.100 inch. The steam ports are also supposed to be 0.125 inch and they are greater than 0.160 inch. Obviously, machining the valve to the drawing (0.500 inch wide) will not work.

What is the best option?

• Re figure valve events with what I have? I’m not even certain I would have enough valve travel.
• or
• I have some 0.0625 inch O1 on which I can machine the correct port openings. Any recommendations on sealing this to the cast port face? Gasket compound or soft solder or whatever?

Castings are great until they don’t allow you to follow the drawings…

John

 

[Bob Sorenson]

Hi John: I built a #4 couple years ago and had the same issue. I recalculated the valve events. I don't think cast iron soft solders. It silver solders tho.

vr Bob

 

[Jasonb]

Mill a shallow pocket and J B Weld in a plate that has had the slots cut into it. I'd make the plate from a slice cut off some cast iron bar.

 

[GRAUBELE]

I once had to increase the distance from the slide box to the cylinder a little.
I made an intermediate plate for this purpose.
This is exactly how the control slots can be repositioned.
Simply make an intermediate plate with the correct spacing of the slots.
You need only one more gasket and the intermediate plate.
And the dimensional position correction on the crankshaft for the eccentric of the slide control.

Dieter

 

[Jasonb]

Pocketing the plate keeps the outside looking the same, this is a larger engine so there was room for screws, and like many fill size engines the valve chest is an integral part of the casting.

 

[timo_gross]

I once had to increase the distance from the slide box to the cylinder a little.
I made an intermediate plate for this purpose.
This is exactly how the control slots can be repositioned.
Simply make an intermediate plate with the correct spacing of the slots.
You need only one more gasket and the intermediate plate.
And the dimensional position correction on the crankshaft for the eccentric of the slide control.

Dieter

In the Elmers Engine that I made a plate like this is in the design. (visible sandwich) it can be only 1 or 2 mm thick.
Maybe a shallow pocket is an option. You could clamp it with the steam chest, it would not be visible, and not require much extra space, not require glue (Maybe I am overlooking the gas seal between cylinder and plate ) or extra screws.


Post how you finally did it. (it might also save the poor guy who drilled at the wrong angle and ruined the port face. Not me! I tried to drill from te port to the cylinder bore and broke the drill inside. (so I have a hole collection of bad cylinders, with various mistakes)

Greeting Timo

p.s. did anyone try SMD solder paste on cast iron?

 

[Jens Eirik Skogstad]

The core used to cast the cylinder on my Stuart #4 does not allow the ports to be machined to the drawings.

This kit was purchased in London in the 1970’s; glad I didn’t have to explain this to current TSA or UK equivalent on my flight back to Los Angeles! Obviously I can’t return the Stuart casting.

Anyway, the exhaust port is supposed to be 0.250 inch and it is, but the lands between the exhaust port and the steam ports are supposed to be 0.125 inch and they are less than 0.100 inch. The steam ports are also supposed to be 0.125 inch and they are greater than 0.160 inch. Obviously, machining the valve to the drawing (0.500 inch wide) will not work.

What is the best option?

• Re figure valve events with what I have? I’m not even certain I would have enough valve travel.
• or
• I have some 0.0625 inch O1 on which I can machine the correct port openings. Any recommendations on sealing this to the cast port face? Gasket compound or soft solder or whatever?

Castings are great until they don’t allow you to follow the drawings…

John

John..

I have experienced many times casting is not perfect in the ports of the cylinder. In total, I have machined and finished 4 steam engines of Stuart 10D and Stuart triple expansion steam engine.

You mill in small cuts until you get the entrance ports in straight parallels without taking too much of the material. The height of the exhaust port is not critical and does not affect by slide valve, only the input port is important in timing to be able to open and close the slide. The sides of the gates are not important, only the height of the gates.

Measure the width between the entrance ports where the slide valve is to close in the middle position and mill to the right width inside the slide valve for the exhaust outlet.

Measure the outermost width of the two entrances + overlap which you can calculate from the drawing is the total length of the slide in outer dimensions of the slide valve.

Along the stroke itself, there is enough space for the slide without bumping into the edges of the steam chest. If in the case , then trim the length slightly larger in the edges of the steam chest so that there is a couple of millimeters of room without bumping into.

 

[comstock-friend]

Thanks everyone for the ideas. At the moment leaning towards Graubele's method as it is 100 % reversable. The eccentric can be mounted the thickness of the plate further outboard on the crank shaft. I have some hard brass plate, we'll hope the bronze (gunmetal) valve likes it.

John

 

[GRAUBELE]

In the Elmers Engine that I made a plate like this is in the design. (visible sandwich) it can be only 1 or 2 mm thick.
Maybe a shallow pocket is an option. You could clamp it with the steam chest, it would not be visible, and not require much extra space, not require glue (Maybe I am overlooking the gas seal between cylinder and plate ) or extra screws.


Post how you finally did it. (it might also save the poor guy who drilled at the wrong angle and ruined the port face. Not me! I tried to drill from te port to the cylinder bore and broke the drill inside. (so I have a hole collection of bad cylinders, with various mistakes)

Greeting Timo

Hello Timo

I'm not sure if it was a question for me or for Jasonb.
My intermediate plate is clamped with the steam chest and two paper gasket between.
With the exact hole pattern of the control slots at the gaskets.

Dieter

 

[timo_gross]

Hello Timo

I'm not sure if it was a question for me or for Jasonb.
My intermediate plate is clamped with the steam chest and two paper gasket between.
With the exact hole pattern of the control slots at the gaskets.

Dieter


View attachment 155572

The question was more a general thought, if anyone who reads it might have tried it.
Because I was cheating so far. Running this "sandwich" without any gasket. In my case for compressed air with no load on the engine this was fine. Does not give big trouble. I found some very thin teflon sheet that was surprisingly useful to make a small gasket for the rear cylinder head. (runnig on steam the leak at this end was too big)




For steam and with some work on the engine, I assume a gasket needs to be there.
Making those small gaskets is really time consuming. I just did not find a good way to to it.

p.s. I indeed overlooked the gaskets at first, now when someone reworks the attention (red arrows) it becomes obvious.

 

[GRAUBELE]

I don't just use ordinary plain paper for the seals.
It is the sealing material from the manufacturer ELRING with the brand name "ABIL".
I think the material should be available worldwide.
With compressed air you can't see any leaks.
When using steam, the steam condenses at the leakage point and you can see the water dripping.
Therefore, steam operation always requires good seals.

Dieter

 

[Jasonb]

I use a liquid gasket rather than paper. Should be able to get it from a motor factors

 

[Charles Lamont]

Wellseal is a good liquid gasket. The method explained by Jens Eirik is exactly what I would have suggested, and means no intermediate port plate is needed. I would only add that if the two steam ports end up slightly different in the distance between the edges (height in Jens' terminology), this can be compensated for by making the exhaust cavity in the valve sligtly offset between the inlet edges.

 

[Mechanicboy]

Measure and correct the errors in the ports that have occurred during casting. Look at the photos that say a lot.