1901-1953 Indian Motorcycle – Parts – Accessories – Service

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  5. Indian Verticals: Tech Tip: Crankshaft & Rods

Indian Verticals: Tech Tip: Crankshaft & Rods

The rotating assembly of your engine (e.g. flywheel, crankshaft, rods, pistons, and all interrelated parts) is where the most time and attention should be given. Consider that if anything is not correct in this assembly, the result is obviously a complete engine tear down and possible failure effects include:

  • Crank journals damaged beyond repair
  • Cylinder sleeves cracked or broken due to excessive rod play
  • Broken rods
  • Cracked pistons

The above failure effects have been personally observed in some of the many engine teardowns that I have completed. These points will be difficult to argue against.

Tip: Have your crankshaft and rod bearings machine ground by an experienced professional.

Rods:

The Arrow, Scout, and Warrior rods were all alike. Care should be given to keeping rods with their original caps. The factory machined these rods as matched sets, and keeping the sets together ensures the housing will be perfectly round. Best practice is to always check concentricity anyways.

Differences in the lower bearing cap nuts can be observed. The image below is of two rods, each with different nuts. The rod on the left has high castle nuts with small cotter pins to lock them. The rod on the right has the more common lock nuts.

The lower rod bearings are made of babbitt and are sized
as STD., -0.10″, and -0.20″. As the crankshaft journal
wears (e.g. the diameter decreases), undersize babbitt
inserts can be installed. These inserts are then custom fit
to a ground journal by means of lapping them to the
required tolerance. The image to the right shows a
disassembled rod with its babbitts removed.

The image to the right shows two NOS replacement
bearings. Both are stamped according to their undersize
amount.
Until replacement babbitts are made available, many
restorers have found Crosley engine rod bearings to be a
suitable substitute (Service Motors at ph. 574-664-3313).
They are narrower, and require machining the lower rod
and cap to accept them. Recently there has been some
success with ThermoKing compressor bearings, as the
Crosley’s are becoming obsolete. Contact Jim Preussner
for information on this setup.

Rods should have very little “play” when installed on the crank journal. If a rod appears to have too much play, carefully disassemble it without removing the inserts and look for signs that the Babbitt has worn through. Good Babbitt should appear as a dull gray color. If there is any portion that appears copper, the Babbitt is worn out and the inserts should be replaced. Below is an image of a worn out journal bearing. Even the copper is worn through in some areas.

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