51. Change over to No.2 lube oil filter and clean No.1 filter.

A、
A、 Turn No.2 lube oil filter to No.1 filter and clean No.2 filter.;

B、
B、 Turn No.1 lube oil filter to No.2 filter and clean No.2 filter.;

C、
C、 Turn No.2 lube oil filter to No.1 filter and clean No.1 filter.
;

D、
D、 Turn No.1 lube oil filter to No.2 filter and clean No.1 filter.