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

To restore proper bearing clearance, I considered boring out and sleeving the original bearings. Then I came up with a better idea. I have some 3/16"(4.76MM) dia. drill rod, which is just enough over the original 4.5MM shaft size to take up the excess clearance in the bearings. Plus, drill rod already has a precision ground finish. All I would need to do is enlarge the bearing holes with a 3/16" reamer.

I had to come up with a way to fixture the engine frame so that I could accurately ream out the bearing holes. Reaming the holes out individually, with a hand-held portable drill would work, somewhat, but what fun is that? If I could come up with a way to mount the engine frame in the lathe, with the bearing holes accurately aligned, it would be a fairly simple manner to ream them out. I decided to mount the engine frame to the vertical slide on the lathe. This allows rotational adjustment in the vertical and horizontal axes, as well as providing adjustment in the x and y axes. Here is the setup I came up with:

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I chucked a piece of steel rod, and turned it down on the end to fit the unreamed bearing holes. This was used to align the engine frame in the lathe until it was clamped in place. I made a stepped clamping shoe from a piece of aluminum to clamp the engine frame to the vertical slide:

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Here's a view looking toward the headstock:

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Making the new shaft was a straightforward turning job, after which it was transferred to the mill to cut two small flats: one for the flywheel setscrew, and one for the governor pulley setscrew. The flywheel was chucked in the lathe, and the threaded hole reamed out to 3/16" dia. Also, a new flywheel spacer was made to fit the larger shaft. Drilling and tapping the flywheel hub for a setscrew was a bit of an operation, as it needed to be at a slight angle to clear the rim. I managed this by tilting the mill head a few degrees:

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With everything now reassembled, the new shaft turns easily in the re-sized bearings, and the flywheel runs dead true. Here's a shot of the finished crankshaft assembly:

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I deemed the accessory pulley too small for a setscrew, and just used some Loctite 609 to lock it on the new shaft (after reaming it out to fit.)

(next up: sight glass seals)