What does SpaceX do with all the engines?

Question

SpaceX has had 8 successful launches in 2016 according to a wikipedia article. The launch manifest agrees with that, but leaves out the launch pad failure.

According to another wikipedia article, they are producing around 200 engines per year:

By June 2015, SpaceX was producing Merlin engines at the rate of four Merlin 1D engines per week, with a total production capacity in the factory of a maximum of five per week.

9 launches gives 90 engines (9+1 per flight), if I am not mistaken. That leaves 110 unused. There are also 45 recovered engines. In principle, SpaceX has a stockpile of Merlin engines for at least 11 launches, so what are they doing with all these Merlins?

Answer 1

... are producing at the RATE of four Merlin 1D engines per week.

That is the key. They have had two stand downs due to loss of vehicles (CRS-7 in flight, AMOS-6 during a test). During that time, they can stop production, when it is clear they have a 3-6 months recovery ahead of themselves. Or else they can assume they will recover next week, continue at the 4/week build rate and only once it is clear their stores are full, pause production.

It is clear that SpaceX has decided that they need modifications to the basic Falcon 9 design for easier, better, faster, cheaper reuse after recovering a bunch of stages. The initial engines recovered first were used for tests. One core is on display with 9 engines at the Hawthorne factory.

One of the cores was fired multiple times at the McGregor test site (JCSAT-14 mission).

One of the cores is being rebuilt into one of the Falcon Heavy demo flight's side boosters. (Thaicomm-8 mission).

One is being reused as a launch vehicle for SES-10 satellite (CRS-8 mission).