A Dying Chainsaw’s Last Words: Top End Rebuild

Unfortunately for me, rebuilding the carburetor was not enough for my 026.  Herein lies the tail of rebuilding the engine of my Stihl 026. I think this has something to do with the problem…

Fair warning.  This post is going to be pretty cut and dry.  No funnies.  No fluff.  If I took as long as I usually do to describe the events that have transpired you would be reading for a very long time. More importantly… I’d be typing and typing and typing forrrr evvvvveeeeeerrrrrr.  Now that that’s out of the way.  Let’s begin!

Doctor!  I need a doctor, the patient is not breathing!

Alright, so here we are again.  The saw didn’t do any better after the carburetor rebuild so onto further work.  When I was given this saw, I was told that it was low on compression.  Time to tear ‘er down and rebuild the top end.  Start by removing the bar, air filter cover, starter, and engine cover.

 

 

Flip over the saw and remove the clutch drum.  Follow along with the photos and you’ll be just fine. To remove the drum, don’t grab the sprocket with pliers!  Just be patient and wiggle it loose.

 

Next, we’re going to remove the handle.  There are 3 screws to remove.  They are located inside each of the rubber “AV” bumpers.  One is at 1 o’clock above the flywheel.  The other two screws are on the the opposite side of the saw along the bottom edge, inside each of the plastic “plugs.”  One plug is located at the chain catcher, the other is at the far edge of the crank case.

 

Now to separate the crank case.  I don’t have a photo of my set up for splitting the case, so words will have to suffice.  I used the corner of my workbench as the surface of contact in the area of the crankcase where the handle attaches.  To further explain…  Look at the bottom of the crankcase… See the area that is empty (where the handle usually lives)?  Slide the saw (flywheel facing up) against the bench so that this area is “filled” by the bench top and that the left side inside edge is sitting against the top of the bench.  Whew, that was wordy.

Get a hammer and gently begin tapping against the crank shaft from the flywheel side.  Continue doing this until the case begins to open at the seam.  Don’t expect or try to make the case come apart in 5 hits.  You’ll probably break something.  Once the case begins coming apart, gently use a screwdriver pry to case open.

Here’s a tip for reassembly, wrap some sand paper around the locating pins and the bearing area of the crank shaft and sand them down ever so slightly.  This will allow you to reassemble the case without needing so much force (which you won’t be able to evenly apply without a press).

Once the case was apart, I went nuts trying to clean out every nook and cranny of this thing. Honestly, the minimum that needs to be accomplished here is to keep debris out of the crank shaft area.  If you’re wondering why I split the case to begin with, it was so that I could replace the main crank case gasket.  You will need to scrape off the old gasket and clean up the surface so that a new gasket can be installed.  I ended up using a flat razor blade to scrape away the material.  A word of caution, the crank case is aluminum and can easily be gouged by the razor blade.  Take it nice and easy and you’ll be just fine.

Once the old gasket and sealant is all cleaned off and you’ve sanded down the locating pins as I previously explained, you’re ready to reassemble.  Give everything one last wipe down and inspect the gasket surfaces for any debris.  All good?  You’ll need to apply gasket sealant to each side of the case in an even and thin layer.  I used Yamabond 4.  Then lay the gasket on the right half of the crank case. Now you’re ready to slap the two pieces together.  Line up the two halves (right side against the bench) and use your hammer to begin tapping the assembly together.  Start by hammering around the crank shaft area with light “circling” taps.  Once the locating pins begin aligning with their respective holes, hammer directly above those areas.  No need to get the entire case completely pressed together, you can finish closing it up with the crank case screws.

Here I have installed the piston rings.  These are made of iron and can be easily broken if you’re hamfisted.  There is a little split in each of the piston rings.  Place the tip of your thumbs in this split and gently spread the ring open so that it will slide over the piston.  Set the ring in the lower of the two grooves on the outside of the piston and align the split with the small pin in the groove.  

Repeat the above process with the remaining ring and place it in the upper groove on the piston. Once you are finished, your piston should look like the one in the photo below.

You will probably notice that the rings seem to be very loose on the piston and maybe you’ll think they are even too big.  Fear not, they are correct.  The reason the rings seem oversized is so that they will compress in the piston ring groove and slide against the inside of the cylinder.  

Here’s how I set the piston into the cylinder.  The first step is to lube up the cylinder.  I used a heavy oil for 2 stroke motors.  It’s 100:1 as compared to the usual 50:1 and worked great for this application.  Why did I put oil on the cylinder?  Lots of scoring can occur while an engine is being broken in because the rings and cylinder haven’t been coated with oil yet.  Spreading a bit of this stuff inside the cylinder before I install the piston gives me a good chance of missing out on some of this premature engine wear.  Ok ok, enough about that.

Line up the piston so that the ring splits are facing away from the exhaust port (rectangular opening in cylinder).  I did actually get a picture of this, so examine the photo if words don’t do it for you.  You really don’t want to twist the piston once you have it seated in the cylinder, so get the alignment as close as possible before you push the piston in.

I used two small screwdrivers to compress the piston rings evenly so that the piston drops into the cylinder.  Take care to not scratch the rings.  If you’d prefer, you can use something like a plastic toothpick.  Repeat the process for the remaining ring and then you can move on to attaching the piston to the piston rod.  In the photo below, I’ve applied the gasket sealant and installed the right side cir clip.  Try to not get the sealant too close to the inside edge of the cylinder.

Before you get ahead of yourself, put the sealant and remaining gasket on the crank case.  It should be located just below the cylinder head (where you removed the original gasket). To link these two items, you need to put the roller bearing inside the hole of the piston rod.  Then slide the piston and cylinder into place so that the inside of the roller bearing and the hole in the bottom of the piston line up.  Once this is done, slide the linkage pin into place and pop the remaining cir clip into the piston. Congrats!  That was kinda fiddly, huh?  

Now you’re ready to bolt down the cylinder head.  Four torx screws are all you need.  If things are going well for you, it should look kinda like this.

Well, not you’re ready to put the handle back on.  Really, this is just a matter of running some screws into place.  The only difficult part of this was getting the impulse line back through the handle.  Good luck with that actually…it was a pain.  I only attached the screw in the handle that is closest to the exhaust port so that I had more maneuverability.  I used needle nose pliers, hemostats, and a small screw driver to get this hose through the opening in the handle.