This will give you a general idea of what is involved when you have a basic engine problem on a 2 stroke engine. The blower in the prictures is a PB500 but it is basically same as the 620. The 620H had a cracked ring and fragments ended up on top of the cylinder. The failure was a result of a crankshaft seal slipping out of place. Unfortunately the engine would still start so the crew ran it until it failed. The first set of pictures show the tear down. The picture of the piston was the actual 620H. YOu can see the damage to the piston. The next to last picture shows one way to get that flywheel off. I used a big screwdriver under the flywheel and a hammer to hit the center bolt. Some times that don't work. The last picture shows the 4 bolts behind the flywheel that have to be taken out to pull the engine apart. The tear down is pretty simple.