What Causes Broken Starter Nose Cones?

Cracked or broken starter nose cones result from a variety of vehicle or installation related issues. Causes include:

starter nose cones

  1. Improper flywheel clearance (tight mesh.) Improper mounting alignment may occur on certain “pad mount” starters due to lack of installing a spacer shim or on “flange mount” starters due to not seating the starter completely flush to the bell housing. Even .015” variance (typical shim thickness) can affect proper mesh.
  2. Engine kickback or backfire. Besides generic timing problems, causes include a faulty Crankshaft Position Sensor (1996-2000 General Motors C/K, G, P, and S/T Series) and electrical system noise interference prompting the ignition module to fire the spark plugs prematurely (Hyster forklifts with 3.0L GM engine).
  3. Starter activation with engine already running. Instances of operator error on older vehicles is one reason why turning the ignition key on most late model vehicles simply sends a “crank request” to the Powertrain Control Module. In milliseconds, the PCM then decides if it’s safe to activate the starter.
  4. Excessive engine resistance. Dirty or improper weight motor oil may cause excessive mechanical resistance to cranking, as can brand new “crate” motors with (initially) tight piston rings.

Missing starter support brackets, loose starter mounting bolts, and harmonic engine vibrations cause most other damaged starter nose cones. The likelihood of preexisting flaws in starter nose castings remains very rare.