Rebuilding the 1987 2F in my 1980 FJ40. Each wrist pin is 20 grams heavier than the stock pins, everything else is exactly the same weight. The reputable machine shop I'm using says that inline 6's don't need balancing as long as all 6 pistons, pins, rods and rings weigh the same. Not believing this, I called several other machine shops who said the same thing. As an automotive repair tech and ex circle track racer, I've always balanced my motors. A little net surfing found this on Wiki.
"An inline six engine is in practically perfect primary and secondary mechanical balance, without the use of a balance shaft. The engine is in primary couple balance because the front and rear trio of cylinders are mirror images, and the pistons move in pairs (but of course, 360° out of phase and on different strokes of the 4-stroke cycle). That is, piston #1 mirrors #6, #2 mirrors #5, and #3 mirrors #4, largely eliminating the polar rocking motion that would otherwise result.
Secondary imbalance is largely avoided because the crankshaft has six crank throws arranged in three planes offset at 120°. The result is that the bulk of the secondary forces that are caused by the pistons' deviation from purely sinusoidal motion sum to zero. Specifically, the second-order (twice crank speed) and fourth-order inertial free forces (see engine balance article) sum to zero, but the sixth-order and up are non-zero. This is typically a tiny contribution in most applications, but may be significant with very large displacements, despite the usual and advantageous use of long connecting rods reducing the secondary (second-order and up) oscillation in the piston motion in those applications."
What do you think? Any advise from you guys who know these motors? Thanks in advance.
"An inline six engine is in practically perfect primary and secondary mechanical balance, without the use of a balance shaft. The engine is in primary couple balance because the front and rear trio of cylinders are mirror images, and the pistons move in pairs (but of course, 360° out of phase and on different strokes of the 4-stroke cycle). That is, piston #1 mirrors #6, #2 mirrors #5, and #3 mirrors #4, largely eliminating the polar rocking motion that would otherwise result.
Secondary imbalance is largely avoided because the crankshaft has six crank throws arranged in three planes offset at 120°. The result is that the bulk of the secondary forces that are caused by the pistons' deviation from purely sinusoidal motion sum to zero. Specifically, the second-order (twice crank speed) and fourth-order inertial free forces (see engine balance article) sum to zero, but the sixth-order and up are non-zero. This is typically a tiny contribution in most applications, but may be significant with very large displacements, despite the usual and advantageous use of long connecting rods reducing the secondary (second-order and up) oscillation in the piston motion in those applications."
What do you think? Any advise from you guys who know these motors? Thanks in advance.