my matsui mwm145w washing machine wont do a spin cycle?

My washing machine will drain but when the washer tries to wash or spin it cuts out lve replaced the carbon brushes even though the old ones were hardly worn with about an inch (25mm) of brush remaining When l changed the brushes l secured the drum with he transportation bolts provided when l purchased the machine The drum turns by hand but does not appear to be as free as it was On other machines lve owned it was possible to tension the drive belt but l cannot see how to do it on this one as the motor is held in place with approx four bolts that do not appear to have any means of adjusting the drive belt tension the machine is approx four years old but hasnt done that much work yet as the original carbon brushes verified Can any one help out please lve racked my brains for a solution