To do this you will need the Simplex & Practik spare parts kit >

Tools required: 

• Allen (hex) key   2mm 
• 2x 10mm spanner (wrench) 
• Cleaning cloths  
• Petroleum jelly (Vaseline) 
• Protective mask and gloves 
• Paper installation tube: 
• 1-piece stout A5 (half letter) size paper 
• Sticky tape & pencil/pen 

What to do 

• Loosen the grub screw in the top of the curved handle using a 2mm Allen (hex) key. 
• Remove the rear locking nut using a 10mm spanner (wrench). 
• Remove the front nut cover and again using the 10mm spanner turn the front nut anti-clockwise and the shaft should turn with it, continue turning until the shaft becomes free.   
• Slowly and carefully withdraw the shaft, the spring will become free, be careful it does not fly out of the assembly.  Fully withdraw the shaft making sure the thrust washer/bearing/washer arrangement from behind the blade holder is retained.  There may also be a small quantity of thin shim washers, retain these also and note their position. 
• Clean all the components and apply a small amount of petroleum jelly to the thrust bearing arrangement.   
• To prepare an installation tube, take a piece of stout A5 (half letter) size paper and draw a line 35mm (1½”) from the short edge and fold the edge of the paper to the line, fold again but along the line itself then carry on folding to the far edge of the paper therefore making a flat tube.  Wrap a couple of layers of sticky tape around one end. 
• Wind up the two legs of the spring and carefully insert them into the paper tube. 
• Reassemble the shaft in the reverse order whilst holding the spring in place using the paper tube. 
• Once fully inserted and screwed in as far as it will go replace the locking washer and tighten using a 10mm spanner (wrench) on each nut. 
• Pull the paper tube away to release the spring.  Loosen the nut on the blade holder end of the shaft by one full turn then slowly tighten again whilst checking for loose movement on the blade holder, stop when all loose movement is removed. NOTE: This nut should not be too tight or it can damage the thrust bearing. 
• Replace the front nut cover finger tight.