I have a Honda Foreman in the shop. This is the standard everyday machine here in rural Alaska.
The owner said that it was hard to start and they thought it was not running correctly. I started it up and noticed right away that the engine was making a terrible rattling sound.
I pulled it in the shop and checked the compression. As I suspected, the compression was very low.
As soon as soon as I pulled the valve cover off I could smell the burnt oil. These engines are air and oil cooled, if they get over heated the oil gets cooked . This photo shows the "fins" where the oil flows over the top of the head. The baked on brown crud is a sure sign of overheating.
When I pulled the cylinder off, the piston was scored. This photo shows my setup for jacking the piston pin out. The paper towels are there to prevent pieces from dropping into the engine. Like most of these small engines, the connecting rod is one piece and cannot be removed from the crankshaft. The pin is held in the piston by two circlips, normally when you take the clips out you can push the pin out by hand. Sometimes it gets stuck and you have to use more force.
It is impossible to swing a hammer in the small area and using a hammer would risk bending the connecting rod. I have found that a piece of all thread with the appropriate size spacers and washers can be used to "jack" the pin out. In this case the pin was stuck in the connecting rod because the rod was overheated/ ran without oil.
This engine is going to need a new piston, cylinder, crankshaft/connecting rod, and all the various gaskets. The parts are around $900 and there is about 12 hours of labor in the job. Pay attention when you change that oil!