Plan to build....steam!!

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I generally don't ream cylinders I bore them.

Unlikely to get a brake hone to fit this engine so turn down a bit of scrap aluminium or even hardwood and use that as a lap, charge with 600g silicon carbide powder and oil mix

I generally don't ream cylinders I bore them.

Unlikely to get a brake hone to fit this engine so turn down a bit of scrap aluminium or even hardwood and use that as a lap, charge with 600g silicon carbide powder and oil mix

View attachment 156265
Yes I'd be confident of a nice finish in the CNC, not so much on my lathe in the shed at home.....I will leave a heap of stock for practice feeds....
See my comments above.
45psi is more than adequate for free running small engines on the bench. - Say less than 1 in bore x 1 in stroke? But good for a performance large boat - say 5ft long. - depending on the engine and speed - IMHO.
But if you want to run a 1in bore by 1 1/2in stroke engine developing some decent power - say for a dynamo - for bench display, then the "fire in the single boiler tube" won't develop adequate quantity of steam, so the pressure will drop rapidly when you try and run the load.
Problem - the Boiler fire tube is just 1 large tube to capture the heat. The burner is only maybe 30mm diameter, and may well be restricted to a gas jet that gives 1.5kW of gas heating power, as lot of which will come out of the chimney as hot exhaust.
Try and find a boiler that takes a much larger burner - positioned beneath the boiler shell and allowing the gases to pass through flue tubes before going up the chimney. That way yo can have maybe 3 times the size of gas burner and much more surface area to take all the heat into the water to make lots of steam for a larger engine.
Do we actuially know if the flue is just a plain bore or more likely has a series of cross tubes which will greatly increase the heating area.
Assume the worst... I have experienced (scrapped) boilers (made by others) that had cross-tubes and had failed due to stress concentrations versus over-pressuring the boiler. If fitted and the job made properly, including calculations - and certified, then all should be OK and safe and durable. But cross tubes also severely restrict the burner you can put in the fire-tube, as they usually take-up about half the cross sectional area of the flue, and cause the burner to be limited to around half of the size you can put in a fully open flue.
My Marine boilers take the flue gases straight thorough a fire-tube, down and beneath the boiler shell, then up the sides of the boiler to the funnel at the top of the casing. Some with exhaust passing through flue tubes going the whole length of the boiler... (depends on "size and simplicity" demand). But my point is that these boilers look OK, and have a pressure rating, but no clues as to BURNER kW rating or how MUCH steam can be delivered. Usually they are the simplest design to "Grab your money" with the nice external appearance.
"Look, No Lagging" = waste of heat and shortage of steam.
At least:
Lagging Kit:
Each boiler is delivered with a wood lagging kit as shown plus fitting instructions...
My lagging is about 1/2" thick (balsa over a composite radiant and thermal barrier) so you can hold the boiler with a bare hand when in steam (but I don't). It really makes a difference to the QUANTITY of steam delivered.
No Superheater - something that really makes a difference to the engine's performance without needing a bigger burner.
But why do they not mention cross-tubes? - probably there are none.
My 3 in dia boiler with a 1.2kW gas blowlamp can power a 5/8" x 5/8" (aluminium body) Stuart Star engine adequately to drive my 48in naval picket boat at a reasonable scale speed (10kn). But cannot realistically do the same with the heavier (cast iron) 3/4" bore and stroke Stuart Sun engine. And it is well lagged, passes exhaust around and through the boiler, has a superheater coil, and re-cycles warm condensate into the boiler. It really needs over 2kW of burner - not in a fire-tube - so it can accelerate to scale max speed for the class of picket boat.
Public Domain,
Sirius' Picket boat 2005.JPG

Shown with Sun engine (low at stern from heavy engine). The photographer wanted it "posed" so was not running...
So "Buyer beware" when buying off the web... ASK the seller about the cross-tubes & flue tube surface area, power of burner, (gas, pressure and jet can be converted to kW), lagging details, superheater, etc. before paying any cash.
AVI file (plays with Microsoft Media Player for me) of the picket boat mentioned above in action. Uncontrolled as the crew have jumped overboard I think?
M'sft isn't good at advising how to convert the AVI file into something this site can accept...(MP4, MOV, etc.). Must go now but will try again later.
If you are extracting more of the heat from the burner due to having cross tubes rather than it going straight up the chimney then the burner doe snot need to be so large as the greater efficiency means you get more from the smaller one. A spiral arrangement of small tubes will take up a lot les sthan half the flue area. Take a look at this boiler for example.,2851.msg56214.html#msg56214

Easy enough for max to contact the maker and ask what the exact build is. They say it will run a boat with twin 19mmdia cylinders so that is something around Stuart D10 size running reasonably fast. Example above also powers a modified D10.
Sorry, the file I attached to post #67 did not appear.
My comments re power of boilers is only my experience, and I am sure there are some better than others. But I have developed an anti- cross-tube idea from seeing the limitations and failures with cross tubes. And from seeing better success and reliability with other designs.
My suggestion is based on trying to help Max get the best for his money. As there u is no mention of boats, just wanting to steam the engine on the bench, an under fired boiler can give more steam than you can get from a marine boiler, and he is not constrained by the size of a model boat hull, so does not really need a marine style boiler.
I imported Clip-champ to convert the old file to something acceptable. I hope it is of interest?

This is what I mean when I describe the boat as capable of scale speed - harbour speed! The wake indicates the "Scale" speed.... or you can time the bow-to stern time to pass a point. Then work it out for a 57ft. boat.
I reckon about 57ft in 3 seconds = 19ft/sec => 13knots.
But these boats were capable of nearer - possibly over? - 20knots when in full steam and "in action"? - which is half as fast again, and I think takes more like 2 1/2 times the power from the boiler. Hence my belief in the limitations of these model boilers with a single flue burner. The next larger jetted burner simply cannot clear the flue gases through the boiler so blows back... and then cannot ingest the air to burn the fuel properly! Current burner (jet no 8) ~1.25kW gas power... next jet size (12) gives ~1.8kW of power. I should need a no. 16 (~2.4kW gas power) to achieve full scale speed for this launch. But that needs twice the diameter of fire-tube and chimney flue. - Or twin burners and a larger chimney than the scale chimney currently fitted.
Of course a bench boiler can be larger, as it isn't constrained by the boat size!
Hope this helps you understand the sizes of burners and boilers?
Sorry, the file I attached to post #67 did not appear.
My comments re power of boilers is only my experience, and I am sure there are some better than others. But I have developed an anti- cross-tube idea from seeing the limitations and failures with cross tubes. And from seeing better success and reliability with other designs.
My suggestion is based on trying to help Max get the best for his money. As there u is no mention of boats, just wanting to steam the engine on the bench, an under fired boiler can give more steam than you can get from a marine boiler, and he is not constrained by the size of a model boat hull, so does not really need a marine style boiler.
So you suggest I would be better served with an upright underfire boiler? I'm not interested in boats at this stage, just a steam plant basically.
Maxjon. An horizontal under-fired boiler gives most space for a large burner. Either a lot of flames, or one that has a large radiant surface (more efficient heat transfer) the some flue tubes through the length before the exhaust goes up the chimney. There is usually plenty of space beneath and at the ènd of the firebox for extra steam tubes as superheater tubes. These add huge amounts of power to the steam without raising the pressure ... the gases around the whole of the shell, and through flues, gives a large surface area for heat transfer to water and steam from the hot gases before losing the remainder up the chimney. In my experience, marine boilers with blow-lamps can be very innefficient, but also the size of the tube limits the burner size. I have 2 boats and a 3rd marine boiler, and all are limited to smaller burners than if I could put a large ceramic burner beneath the boiler shell. Here's a "packaging" job to fit inside the boat hull.
Tomken 1.JPG
Tomken engine room.JPG
And another outside the boat.
Sirius Sun engine & boiler.JPG
Vertical boilers can be quite good with a lot of small flues. But the compromise is that the radiant surface is reduced to the area of the end of the cylinder, less area of flues where radiant heat shines straight tthrough. Put the same cylinder horizontal with only half to 2/3 the flue tubes and a good radiant burner can be not only larger, but more efficient at transferring the radiant heat to a larger area (cylinder side), and still transfer much of the heat through the flues.
On the burning gas view, a vertical boiler usually has limited space for completing combustion before flames go into flue tubes, when the temperature drops and CO combustion is extinguished.
An horizontal boiler can be easily made with a larger space to complete the combustion before the exhaust cools to extinguish CO combustion.
I hope this helps?
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Here is a boiler I am repairing: 3 in diameter and 6 in long.
Before strip-down (in its casing) but with water gauge, smoke box and chimney removed20240206_154833[1].jpg20240206_154843[1].jpg:
After some repairs. (Stays added: still Work-in-progress!):
And the burner:
This is currently dismantled for re-sealing. (after 25 years use!)

Here's another boiler I have repaired and needs cladding (Insulation) adding. - 3 3/2in dia x 8 in long.
And here is a burner of around 3kW that will suit either of these horizontal boilers.20240508_135247[1].jpg
Or full-on:
Inside the fire-box there is a change of gas dynamics, and the "back pressure" causes the flame to be more uniform across the burner. This burner is between 2 and 3 times the "power" of the burner I can fit inside a similar sized Marine Fire-tube boiler.
Hope this helps?
Is that burner one from Stewart?? I have a Stuart 504 boiler that somebody long ago replaced the older wick style burner with 2 others that I can't identify. Are there other options for burners either here in the US or other places?? Have not decided if I want to just look at it or get into live steam. Currently use compressed air to demo my other engines.
Burners are Home Made from ceramics I buy from the web. £10 each. The tin is often a sardine tin, kipper ti
nm or other suitable sized tin to save making one. But I also make in aluminium, brass and from tin cans cut open for the sheet tin-plate, and my largest used a biscuit tin. (I call it Up-cycling!). I make my own jets from 0.25mm upwards, but if I am making a tiny burner and need a 0.2mm or 0.15mm drill - I don't bother, I but the No 5 or no 3 jet and don't worry about the cost. Cheaper than my skill with small drills!
If you want a design, PM me and I'll oblige if I can? Even make and sell you a burner if you prefer? (I have sold many on 3&@y but there isn't profit in it so now only to friends)
I suggest you speak to your local club about re-commissioning the boiler. It will need a 2 x NWP Hydraulic test, after a visual examination, then a steam test to prove the Safety RELIEF valve relieves at < 1.04 x NWP (max 4% overpressure) - with the burner on full and all valves shut. Then you'll get certified for a year or 2... - And the Insurance Company will cover you....
Hope this helps?
Thanks for your reply.

My primary purpose of the post was to gather information about burner alternatives as the burners are non functioning. The NC Dept of Labor has a specific section on "Hobby Boilers" with details as to what is required. (somewhere ran across a site that had a listing by states with links to applicable regulations - super helpful!! Understand these often vary by state at least here in the US.) After seeing what was involved, basically had decided to pass the boiler along including what learned and stick with compressed air for demonstrations and shows.
Aha! I found this one... 13 - labor/chapter 13 - boiler and pressure vessel/chapter 13 rules.html
Which cites the simple rules that I adhere to in the UK (with local variation) except it costs me my annual membership of a club instead of your $50 fee.
So (forgive me stating what you can read on the links):
  • "Model hobby boiler" means a boiler that generates steam, whether stationary or mobile, and is used for the purpose of entertainment or exhibiting steam technology, where the boiler does not exceed
    • i) 20 square feet of heating surface;
    • (ii) a shell diameter of 16 inches;
    • (iii) a volume of 5 cubic feet; and
    • (iv) a pressure of 150 psig; (Silver soldered copper boilers should not exceed 100psi according to ASME).
  • Hobby boilers, locomotive boilers and exhibition boilers shall be inspected annually, at the beginning of the season when they are anticipated to be operated.
    • Internal Inspection Hobby boilers: certification cost: $50.00
    • In addition to the requirements outlined in this Chapter for manually fired boilers, model Model hobby boilers shall meet the following requirements:
    • (1) Each boiler shall have as a minimum:
    • (a) A properly operating pressure gauge that shall not be less than 1 ½ times nor more than four times the operating pressure of the boiler;
    • (b) Two safety relief valves each of which shall be capable of protecting the boiler from over pressurization. Requirements for ASME/NB certification are waived. If an ASME/NB safety relief valve is utilized, only one safety relief valve is required;
    • (c) An easily accessible mud-ring valve;
    • (d) A water gauge glass; and
    • (e) If constructed of copper, a fusible plug in the top of the crown sheet.
    • (2) Upon successful completion of the inspection and payment of the fees, the Chief Inspector shall issue a Certificate of Inspection valid for one year.
    • History Note: Authority G.S. 95-69.11; 95-69.14;Eff. July 1, 2006; Pursuant to G.S. 150B-21.3A, rule is necessary without substantive public interest Eff. July 22, 2018. 2018; Amended April 1, 2022.
Realistically, having 2 Safety Relief valves isn't a major issue.
The "mud-ring" valve is just the Blow-down valve in UK terms. A good idea but not compulsory in the UK. Useful for emptying the boiler after use...
The "fusible plug" applies to copper boilers with a firebox that must be covered by a water level covering the crown sheet, as most loco boilers, but may be something in a proprietary bought boiler, if it is appropriate for the actual boiler design selected? (e.g. A vertical bench boiler with firebox?). A US maker of boilers you can buy should explain this in his certification when you buy the boiler. (e.g. I doubt a non-US one would have that!).

I suggest you don't simply give-up, as the rewards of running live steam at a show are worth it in my experience.
That US code covers larger boilers than are likely to be tested at club level in the UK

at 5cu ft they will soon exceed out 500bar/ltr maximum but at the other end of the scale we have a set of test requirements for very small boilers which the type being discussed may well fall into that require a lot less f a hobby boiler. Then there is one in the middle that would cover loco and smaller traction engines.
Since you asked earlier about the boiler and burner, I have almost finished re-building the ceramic that is over 25 years old and getting tatty.
I recently played with jets as it will run a bigger gas jet than I was using. (0.3mm) no. 8.20240510_175348[1].jpg
I had decided a 0.4mm was sensible:
- Without over-heating the burner to melt-down!
I also altered the internal baffle (removed it) in favour of some "swarf" - coils of aluminium - to act as "gas flow disturbers" and encourage the initial part of the burner to ignite.
This means that when in the boiler firebox, the change of "hot surroundings" and back pressure will cause the fire to burn over more surface area than before. But I also figured that a bit more air, and more length of mixer tube could improve it further? - The maths goes: The jet provides a fixed input of energy converted to 1/2 mVsq. kinetic energy of gas. The high velocity and developed sub-atmospheric pressure of the gas jet sucks in the air, but the law of conservation of momentum means the gas jet at high velocity becomes a gas and air column at lower velocity. (More mass = less V). Then expansion along the mixer tube converts velocity into pressure, so the positive pressure can push the gas mixture through the pores of the ceramic, keeping the ceramic cool, and keeping the flame front from burning back to the jet! I want more "pressure in the burner plenum" and less velocity, so adding air is a good thing - up to a point.
So I added a small extension with an extra pair of air holes:

I think this is an improvement!
So now I'll make a proper single jet holder to intake venturi and mixer tube.
Hope this is of interest?