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A Very Special Thomas Flyer – Re-babbitting and boring the connecting rod bearings

Progress is being made on the 1910 Thomas-Flyer being mechanically rebuilt here in the shop and this post shows you the process of re-babbitting and boring the bottom end of the connecting rods to finish size. First off a little bit of information about the precision rod boring machine, which is used for this operation.

This machine dates to the 1930s and was one of a batch the LeBlond Machine Tool Co. made up for Federal Mogul, the well know bearing company. The company used them in their regional re-babbitting facilities. This one came out of the Hartford, Connecticut, branch and it was restored here a few years back. This type of connecting rod lathe is close to impossible to find today as most of them were scrapped in the 1960s after modern insert bearings became common.

It can bore all the way up to a 19.5-inch center-to-center long rod and it has been used here once, to bore the rods on a ’20s Caterpillar engine that were close to that length and the crankshaft was a bit over 6 feet long. It is five feet wide, by five foot tall and weighs in at somewhere around a ton. In spite of being 80 years old it is one of the smoothest running machines in the shop and produces an unbelievably smooth surface cut.


The rod gets set up on an precision expanding mandrel (left above) on the small end, which is held at the top. The center to center distance is set by the crank and lead screw on the vertical column and it is accurate to .001 an inch. (one thousandths). The bottom of the rod is held by a two-jaw chuck, which centers it over the horizontal boring bar. The cutter, which is held in the boring bar, is set with a boring rod mic (center above) to the size of the cut that you want to take.

The bar rotates at up to 3,500 rpm and the carriage of the lathe moves the rod sideways and feeds it over the spinning bar. The two disc-shaped pieces on either side hold fly-cutters so that you can machine the rod thrust faces on each side to the correct width and also cut a chamfer on each side so that it will clear the radius on each side of the rod journal on the crankshaft.


The Thomas rods as shown (above left) after fresh babbitt has been poured into place and after the first rough clean up of the parting faces (precision finished before boring). The (center) photo shows custom machined bronze connecting rod bushings for the top ends. The (right) photo shows a bottom end after oil grooving and machining the bore to size and facing the side thrust surfaces.

You can also use this machine to rebore the bottom end of re-babbitted inserts or the bottom of damaged rods (followed by honing) and then the machining of new larger inserts. The new rod made by Cunningham (below) and the inserts first machined from bronze and then babbitted for a Mercer, show the other style of babbitted inserts that are also used in early cars, after finish boring to size.

You can see three pages of our earlier posts here on the Thomas-Flyer 6-70 (just scroll down).

11 responses to “A Very Special Thomas Flyer – Re-babbitting and boring the connecting rod bearings

  1. I really enjoy the articles regarding the re-manufcturing and machining of parts for these great old vehicles. I especially like the tooling and setup notes. I worked at LeBlond as a manufacturing engineer years ago, before and after they were purchased by Makino. The older machinists in the shop were just terrific craftsmen. You should have seen the crankshaft lathes we built!

      • As I recall it was early 80s. There was an order for 2 machines, the old drawings had to be unearthed, lots of special parts made. There were only a few (old) shop guys and engineers left who knew how to build the machine. It was right around when Makino bought them out and stopped all of the LeBlond production. I know I was fascinated to see it work when it was being runoff prior to shipping! A LOT of “monkey motion”! Sorry for the delay in responding.

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