encumber vs throw a spanner in the works

encumber

verb
  • To restrict or block something with a hindrance or impediment. 

  • To burden with a legal claim or other obligation. 

  • To load down something with a burden. 

throw a spanner in the works

verb
  • To introduce a problem, dilemma or obstacle, something unexpected or troublesome. 

How often have the words encumber and throw a spanner in the works occurred in a corpus of books? (source: Google Ngram Viewer )