Replace or Rebuild?

This is not a new concept.

First there was "engineering economy" which all civil engineers were required to take (you will be asked at least one question on the PE exam).

Then "value engineering" on government funded projects by EPA.

More recently, "life cycle cost analysis" is the buzzword.

All of these methods attempt to determine the best "viable" alternative by considering true cost (take into account inflation).

ENR (Engineering News Record) Cost Index goes back at least 100 years.

These same principals can and should be applied to a production process.

Some questions i'd ask myself: 'Will the replacement eqpt. be more efficient than the old?' , then: 'Am I more/less likely to be able to obtain spares in the future?'

there are solutions for rebuilding worn machinery, that change the equation: the posibility to apply on site, in operation, a new surface treatment and renew metal surfaces for many more years of operation, at a fraction of the cost of part replacement.

We applied this treatment to gears, bearings, vacuum pumps and compressors, with total success. see www.rewitec.com

Here you are identifying an alternative (repair/rebuild). Let us call this Alternative No. 2.

This is an important step. When available and viable alternatives are not first identified, the outcomes over the life-cycle of the (plant, machine, process, whatever) are not optimized.

So your decision tree may look something like this:

1) replace widget.

2) repair widget.

3) Partial replace widget.

4) No action (do nothing).

So, in this case, Alternative No. 2 has been considered (previous management team never considered "repair" alternative), all cost numbers where calculated over the life-cycle and Alternative #2 was chosen as the best viable alternative, all things considered.

Considerations may include reliability, cost, performance, maintenance, etc.

Costs must include labor, equipment, materials, everything! All costs must be converted to Present Worth $ over the entire life-cycle. Use sinking fund, present worth, etc. cost tables to complete the analysis.

Go back & read your post. The answer is the post itself. Good Luck