Tuesday, July 26, 2011

Replacing the chain oil pump on a Stihl 034

While running my chainsaw, I noticed the chain was getting tight on the bar, and not operating free.  As I examined it closer, I found the bar was not being oiled. It turned out that my oil pump had stopped working.  Here's how to replace it.

  1. Get out your tools.  The 034 comes with a rudimentary tool kit that has almost everything you will need.  A flat head screwdriver, a number x torx, a 5/8th socket, you will also need a small flat head screwdriver, and a pair of needle nose pliers.
    The next four steps are pretty routine.  If you have never removed these parts, this guide is not for you.
  2. Remove the cover from bar, and remove the bar and chain.  
  3. Remove the air intake cover from the back of the saw (quarter turn on the locking knob and pull up).
  4. Disconnect the spark-plug wire (pull straight from plug).
  5. Remove the top cover (flat head screwdriver to loosen the screw on the top).
  6. Remove the flat head screw that holds the metal chain guide plate on, and remove the plate too.
  7. Drain the oil from the bar oil tank by removing the cap, unhooking the retaining chain, and pouring the oil into another container.
  8. Remove the two torx screws holding the plastic cover around the flywheel, and lift the cover off.
  9. Pry the lower cover up from near the bottom -- carefully.  It has a post on it that presses into a hole, so it you pry off to the side, you risk breaking this post.
  10. Using a small flat head screwdriver, remove the snap-clip that holds the sprocket drive in place.
  11. Lift off the washer and sprocket.
  12. Lift off the flywheel.  
  13. Remove the strap that stops the flywheel.
  14. Remove the spark plug.
  15. Now comes the tricky part.  To remove the clutch wheel, you have to stop the piston from going up and down. Stihl makes a special tool that is inserted through the spark plug hole and blocks the piston from moving.  We are going to use a clean (emphasis on clean) rope.  Thread a bunch of the rope down into the cylinder to fill it.
  16. The clutch has left-hand threads, so turning it clockwise will cause the piston to block against the wad of rope in the cylinder and then loosen the clutch.  
  17. The assembly that sits below and has a loop around the crankshaft is the oil pump.  Remove the nylon worm-drive gear from the center by turning it clockwise.
  18. On the bottom of the saw, turn the oil feed all the way in.
  19. Remove the two torx screws from ring on the oil pump that goes around the crank shaft.
  20. The pump is pressed down into a ring recessed into the crank case.  You have to pry it out.
  21. The pump comes with a new oil line so remove the old one -- and you are going to destroy it getting it out. Start by locating the brass grommet that fits inside the end of oil line where the oil is supposed to be coming out.  I had to dig at mine pretty aggressively to get enough of it exposed to grab it with a pair of needle nose pliers and pull it out.  
  22. Pull the oil line and the oil pump out.  Yay.  
A chainsaw is a pretty dirty environment.  Spend some time cleaning things up before you start putting it back together.  The grommet that creates the seal between the pump and the reservoir is really a flange on the end of the oil pickup tube.  I suggest removing it as well and cleaning it out with some compressed air.

Reassembly:

  1. Clean out the grove in the crank case where the oil pump presses in. This is important because if you don't the oil pump may not seal and pick up oil from the reservoir.
  2. Feed feed the new oil line into it's passage way.
  3. Put the two torx screws in to hold the oil pump in place.  Tighten them incrementally, alternating to minimize binding, but making sure the oil pump is securely seated.
  4. Put the thrust washer back against the crank case.  
  5. Put the bushing on the crank shaft. 
  6. Thread the worm gear back onto the crankshaft.
  7. My pump came with what looks like a long spring for a pen.  That spring is to keep the oil line from kinking.  Slide it inside the oil line.  Press the new brass bushing into the end of the oil line to the line in place.   
  8. Thread the the clutch on to the crankshaft (remember it is left-hand threads).
  9. Slide the roller bearing onto the crank shaft.
  10. Slide the flywheel onto the crankshaft over the roller bearing.
  11. Put the sprocket back on.
  12. Put the thrust washer back on.
  13. Put the snap clip back on.
  14. Put the strap that stops the flywheel back on (make sure the break is disengaged).
  15. The rest of the reassembly is just reversing the remaining steps.
  16. Before putting the bar back on, clean the chain grove in the bar.  Also, take a look at where the oil line feeds the oil through the small hole in bar and clean it out too.
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