... life. As a general rule, we recommend that the brushes be set at 4 psi pressure. To calculate the ... at equal distance around the commutator. For a 4 pole machine, the spacing will be every 90 ... , brush wear, and commutator wear.Machine Neutral:To obtain optimum machine performance, the brush must be ... you may observe sparking under a no-load condition. Depending upon how far off neutral the machine is ...