Tractor Repair: b 414 IH diesel tractor, crankshaft pulley, harmonic vibrations

Question
Hello Arnie,
  I have used this tractor for the past 10 years to mow grass with. It has never had any repairs that I know of; ran great with no problems. I first noticed a slight vibration in the engine, and after a few weeks was worse with bumping sound. I pulled the oil pan off, and 2 main bearing caps are broken laying in pan. The 2nd and 3rd from flywheel. One bolt on each broke, and then the cap  broke next to the bolt left in block on both. What do you think could have caused this? I have considered trying to find 2 more caps; and using plastigauge to fit them; but am afraid problem may still be there. Do you know where I might be able to find the caps and any advice would be greatly appreciated.
                               Thanks,  
                                Steve

Answer
Hello,

  It would be impossible for me to determine an exact cause, but here are a couple of things to check.  Check for a loose flywheel or front crankshaft pulley.  They can set up harmonic vibrations that could cause it.  Every rod and main bearing and the entire crankshaft should be checked for a defect.  Also check for a broken crankshaft.  This is not as easy to see as you might think.  The pieces will still fit together and rotate as a unit, and you might only see a fine crack so you have to look very closely.  Bearing caps should be obtainable from a tractor salvage yard, but they might need to be align bored by a machine shop because the caps and engine block are bored together when they are made.

                    Good luck,

                          Arnie