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

I appreciate all of the positive comments! The weather here has taken kind of turn, as Fall seems to be asserting itself a bit. Thought I'd stay indoors today, and catch up on some of the documentation for this project. I'm pretty much finished with all that (I think!) needs doing, short of a final run test. I've done several tests with compressed air, and one under steam, which revealed areas that need work.

In the last installment, I was bemoaning the state of the filler cap thread, and vowed to do something about it. I want to keep the original cap, for aesthetic reasons, but replace the weak threads with a slightly larger new thread. The original thread size was not any size I was familiar with... U.S., Metric, BA, etc. The closest I could come up with was 9/32-32. I decided to go up in size a bit, and use 5/16-32, which is a fairly common ME ("model engineering") thread, and I have a tap and die for that size. I will also make a bushing for the boiler, as really should have been in the original design.

I'll machine off the old thread, and counterbore slightly for a 5/16-32 brass threaded piece. This will be held in place with a #4-40 stainless threaded stud (leftover from another project), and Loctite 620 hi-temp retaining compound. The brass threaded piece will also have a step to retain a captive PTFE washer. Here's the drawing:

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To hold the cap in the lathe, I made a little fixture from a piece of 7/8" dia. aluminum. It was counterbored to fit the O.D. of the cap, and drilled & tapped for (4) retaining screws:

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After removing the old thread, counterboring, and tapping for the #4-40 stud, this is how it looked:

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A 5/16-32 threaded die, mounted in the tailstock, was used to make the new brass threaded piece. It was then drilled and tapped for the stainless stud. With the teflon washer in place, the parts were assembled using Loctite 620. Here's the finished cap assembly:

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Next step was to make a 5/16-32 bushing for the boiler. I reamed out the threaded hole in the boiler, and counterbored slightly to accommodate a brass bushing:

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The bushing was soldered in place with Stay-Brite 8:

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Here's the finished cap assembly installed on the engine:

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With that part of the job completed, it was time to focus attention on the crankshaft.

(to be continued)