Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I am with @Stoker!

I feel your pain on dealing with sight glasses and getting the seals (and spraying out hot water when you think they are okay)!

I'm not sure exactly how the original sight glass was sealed to the boiler. There is a 2-bolt clamp at each end of the U-shaped sight glass, retained with tapped holes in the boiler. A shallow counterbore surrounds each sight glass hole. How this was all sealed up originally, I don't know. Upon disassembly, there was evidence of repair attempts in the past.

Because of their flexibility, and wide range of sizes, I prefer o-rings for sealing jobs like this. I made a CAD drawing which shows a section through the boiler and sight glass, on the centerline of one of the fittings. It shows the original hole enlarged with an 82 degree countersink, with a silicone rubber o-ring and brass washer. The 2-bolt clamp will compress the o-ring, and wedge it between the sight glass and the 82 degree countersunk hole. The brass washer was needed because the hole in the clamp was to large to properly compress the o-ring.

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I had some concerns about cracking the sight glass with this setup if the countersunk holes were off center, or misaligned in some way relative to the holes in the boiler. To assure proper alignment, I decided to make a pair of brackets to precisely align the boiler in the mill. These would consist of some 1/2 x 4" aluminum plates, 4-1/4" long, with a 2-3/4" hole in each. They would be saw-cut thru the center, and drilled & tapped for some clamp screws. I used a 2-1/2" dia. hole saw to rough out the holes:

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A boring head was used to enlarge the holes to the full 2.750" diameter:

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The top of each bracket was center-drilled on the exact centerline of of the 2.750" hole. This would enable the mill spindle to be easily aligned with the hole in the bracket, and could thus be used to align the holes in the boiler at "top dead center" in the brackets. Here is a shot of the engine mounted in the mill vise with the with the boiler brackets. A 60-degree center in the spindle is used to establish alignment:

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With the boiler retained and aligned in this way, it's an easy task to drill the countersunk holes in precise alignment with the boiler, and at the exact spacing of the sight glass ends. Also, the depth of the countersunk holes can be precisely set. Here's a view of the boiler with the finished holes:

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Preparing to assemble the sight glass, o-rings, brass washers, and seal clamps to the boiler:

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Sight glass, o-rings, and brass washers installed in the countersunk holes:

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Seal clamps installed. Note that the clamp screws will need to be removed when the sight glass guard is installed, as it uses the same screws as the seal clamps:

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Hopefully this installation will prove satisfactory. The o-rings are rated up to 450F degrees, so there should be no problem on that score. The screws will need to be sealed at final assembly, as they thread right thru the boiler shell. There are a total of twelve(!) threaded holes in the boiler that need to be sealed in some way.

No kidding! If you notice, in one of the pictures of the sight glass, you can see what looks like a crack in the inside of one of the bends.     I was worried about this at first, but it seems it is just a shallow groove used to mark the location of the bend. I would hate to have to make a new one.

How much heat is required? Can a propane torch be used, or something hotter? [ Guests cannot view attachments ]

Thanks, Stoker. Hopefully I won't have to bend one for this engine, but it's good to know that making a new one isn't too difficult.

100% Awesome!  Well done... you can now send it to me to keep it safe ;-)

Paula, your work is superb!