Saturday, August 30, 2014

Steam Engine Restoration Part 10 (Video Post) - Casting New Babbit Bearings

After months of research and watching tutorial videos, I finally took the plunge and started the process of casting fresh crankshaft bearings for my steam engine.

This engine uses Babbitt bearings on the crank, which are cast in place between the structure of the machine and the rotating shaft it will be carrying. These were extremely common in old industrial machinery and engines of all types because they could be easily made to a high tolerance using basic hand tools.

Engines that utilize these bearings have hollow bearing blocks, which act as cups that hold the finished bearing in place. To cast the bearing, the rotating shaft is placed into the bearing block and suspended in the correct location using shims or collars. I machined a pair of steel shims that rested on the edge of the bearing block and held the crank vertically in place.

Crankshaft locating shims

The steam engine base with crank shims installed
I purchased a used casting ladle off of Craigslist and melted down the Babbitt metal brick using the propane forge. This burner maintained steady heat and quickly liquefied the brick. 

Finally getting to use the propane furnace!

Melting the Babbitt brick
 I packed clay between the bottom of the crank and the bearing block and poured the molten Babbitt into the cavity (detailed above in the video). After cooling and trimming down the excess material, the bearings were ready for test fitting. The next step is to pour the bearing cap bearings.

Trimmed and installed in the bearing blocks

Bearing halves removed for cleaning

The crankshaft installed in place for test fitting.

Wednesday, August 13, 2014

Steam Engine Restoration Part 9 - Shimming the Bearing Surfaces

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

Package of steel shim material of multiple thicknesses

Determining the required shim thickness with feeler gauges

A pair of shims for the valve slid cover. Loose enough to not bind, but tight enough to keep from rattling.

Boring a grease passage in the wrist pin

This will allow grease to be pumped directly to the bearing surface from the end of the wrist pin

Tapped to accept a Zerk fitting

Shims installed in the top of the connecting rod. This sets the fit between the rod and the wrist pin. 

Checking final fitment.

Modified wrist pin re-installed. Now the joint can be lubricated without disassembly.