The next step in the re-assembly of my steam engine was to measure the clearances in the bearings and install spacer shims. Vintage engines, especially those with babbitt bearings, require the use of shims of varying thickness to achieve the correct fitment tolerances in the bearings and sliding surfaces.
Additionally, these shims increase the service life of the engine by allowing you to tighten-up worn bearing surfaces. By replacing the shim in a loose bearing with a thinner one, the "slop" in the bearing is eliminated.
I purchased a set of steel shim stock from McMaster. This set came with individual sheets in a wide range of thicknesses. I have heard from some sources to use brass shim stock, but carbon steel is (effectively) noncompressible, so it will not get hammered thinner by the reciprocating motion of the engine.
While I had it in pieces, I also took the opportunity to drill a grease passage in the wrist pin, so that the upper bearing of the connecting rod can be lubricated without requiring disassembly
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| Package of steel shim material of multiple thicknesses |
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| Determining the required shim thickness with feeler gauges |
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| A pair of shims for the valve slid cover. Loose enough to not bind, but tight enough to keep from rattling. |
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| Boring a grease passage in the wrist pin |
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| This will allow grease to be pumped directly to the bearing surface from the end of the wrist pin |
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| Tapped to accept a Zerk fitting |
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| Shims installed in the top of the connecting rod. This sets the fit between the rod and the wrist pin. |
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| Checking final fitment. |
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| Modified wrist pin re-installed. Now the joint can be lubricated without disassembly. |
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