Estimate the manual assembly time and design efficiency of

Estimate the manual assembly time and design efficiency of the piston assembly shown below. Suggest a redesign of this assembly to reduce the number of parts and increase the assembly efficiency. Estimate the manual assembly time and design efficiency of the redesigned assembly.
The assembly sequence of the piston assembly is as follows:
 The base is placed in a fixture.
 The piston is inserted into the base. The piston must be carefully aligned, because the piston rod does not engage the hole in the bottom of the base before it must be released.
 The piston stop is inserted into the cylinder.
 The spring is inserted into the cylinder and tangles severely with others in bulk.
 The cover is placed onto the base and held in place to maintain alignment.
 The two screws are inserted and driven home to secure the cover.
Figure: Piston assembly (dimensions in mm).
II. Perform a literature search to uncover reports where the applications of DFA or DFMA-type studies have resulted in product simplification or reductions in manufacturing costs. For each report give the reference and a brief summary of the findings.
III. The report will have cover page, content, abstract, statement of concept, principle, overview and analysis, critical review of related literatures. Citations are required.