Hi; Since I joined this site I have read a lot about porting and modifing cylinders etc. A week ago I came across a Stihl 028 woodboss in excellent cosmetic condition and was told the saw had low hours useage. The owners 15 year old son had decided to clean up the saw for his dad and for some reason thought he could remove the flywheel nut by removing the muffler and inserting a 3/8 threaded bolt through the exhaust port over the piston and then twist off the nut in a clockwise turn. Well when it did not come loose he did try in a counter clock twist and got it off only to discover he could not remove the flywheel any way and then replaced and re torqued the nut, removed the bolt and pulled the recoil .
The piston moved a bit then stuck in the bore, more pulling and eventually the pull cord snapped. The son eventually told his dad the saw was running and just stopped dead. They put the saw up for sale to get rid of it and I picked it up for 50. After dismantling I found the damage and the piston crown was squeezed down hard on the right side so tight it split the top ring and in the left side of the exhaust port it dented the piston crown leaving thread marks from the bolt in the piston.
I ordered a new piston and rings,pin and keepers and figured this would be a good candidate to do a mild porting job on. This is my first such undertaking and I only removed 15 thou. off the top and sides of the exhaust port and 10 thou. off the intake bottoms and transfer ports. I made a new 5 thou. gasket and after a light hone and radius job on all openings in the cylinder I cleaned , washed and dried the cylinder. Fitted up and installed the new piston and rings well lubed and reinstalled all parts to get ready for start up. I only bolted on the back portion of the muffler shell and on the first pull the saw started and idled for two minutes before giving it throttle. It stumbled for a split second then responded with an ear splitting roar and has ran excellent since. After installing the two front muffler covers it ran quiter but seems to be suffering from the restrictions of the small exhaust ports in the muffler.
The exhaust port size at the head is now around 26mm wide and 13 mm high, the muffler has a turn down deflector where the exhaust flows down into the plenum first then turns up through a port that is 6mm by 37mm where it reaches the top of the muffler front cover then is returned back downward through a similar sized duct to exit the muffler front. This seems too restrictive and does not allow the saw to breathe. I removed the muffler front covers and the saw comes alive but would wake the dead as my ears are still ringing two hours later. Does anyone out there have any suggestions on how much to open up the muffler or is there a better muffler available, a dual port maybee? Pioneerguy600
The piston moved a bit then stuck in the bore, more pulling and eventually the pull cord snapped. The son eventually told his dad the saw was running and just stopped dead. They put the saw up for sale to get rid of it and I picked it up for 50. After dismantling I found the damage and the piston crown was squeezed down hard on the right side so tight it split the top ring and in the left side of the exhaust port it dented the piston crown leaving thread marks from the bolt in the piston.
I ordered a new piston and rings,pin and keepers and figured this would be a good candidate to do a mild porting job on. This is my first such undertaking and I only removed 15 thou. off the top and sides of the exhaust port and 10 thou. off the intake bottoms and transfer ports. I made a new 5 thou. gasket and after a light hone and radius job on all openings in the cylinder I cleaned , washed and dried the cylinder. Fitted up and installed the new piston and rings well lubed and reinstalled all parts to get ready for start up. I only bolted on the back portion of the muffler shell and on the first pull the saw started and idled for two minutes before giving it throttle. It stumbled for a split second then responded with an ear splitting roar and has ran excellent since. After installing the two front muffler covers it ran quiter but seems to be suffering from the restrictions of the small exhaust ports in the muffler.
The exhaust port size at the head is now around 26mm wide and 13 mm high, the muffler has a turn down deflector where the exhaust flows down into the plenum first then turns up through a port that is 6mm by 37mm where it reaches the top of the muffler front cover then is returned back downward through a similar sized duct to exit the muffler front. This seems too restrictive and does not allow the saw to breathe. I removed the muffler front covers and the saw comes alive but would wake the dead as my ears are still ringing two hours later. Does anyone out there have any suggestions on how much to open up the muffler or is there a better muffler available, a dual port maybee? Pioneerguy600
