Hitachi C10FC sparking commutator

Inherited this Hitachi C10FC dropsaw, and noticed excessive sparking around the commutator. Pulled out the brushes and noticed they were worn down to nothing. Replaced them with new brushes , used saw for a short time and noticed sparking!. Inspected new brushes and noticed serious erosion on one side of the brushes. What could be happening here ?, Note that there are two windings on the field and the finer one is open circuit - is this a braking winding, and could its failure affect the normal running of the motor ?. Any ideas appreciated. Cheers Mike
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Site Timeline is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.