DS21 & DS21M / DS19A & DS19MA Repair Manual — Page 188

22. Stripping the cover. a) Remove the pipe assemblies. b) Compress the return springs of the gear change control pistons: Using tool 3171-T will save time on this. After compressing the spring, hold the piston in this position with the aid of a screw (4) 4mm diameter x 40 mm long under the head (plain washer under the head). If the tool is not available, use a screw (3) 4mm diameter x 80 mm long under the head, with a nut and plain washer.