Chainsaw Repair

"Quote " Now, coming to the transfer ports, they would have a retarded timing because the piston top opens them, right?

Depends on how you look at it and who's theory you subscribe to .By lowering the cylinder and leaving the top of the transfers as they were in theory the crankcase pressure will be slightly higher when they open .

For example many Stihls have a transfer opening 20 degrees after the exhaust port opening .Ample for the stock running RPMS but not enough time for complete blow down if running at speeds exceeding the factory designed speeds .

If the compression is raised high enough by the initial lowering of the cylinder and the exhaust port raised a few degrees it gives a longer blow down and thusly a more "cleansed " tranfer of fuel and purging of the residual exhaust fumes .Therefore making the next power stroke more effective .---at least in theory 

Now things can be improved by using external secondary transfers or internal finger ports but that gets into the catagory of race saw engines .

The biggest challange in the conversaion of transfer ports is the abilty to "sweep " the area above to intake port .Now on that my theory or one I use is with a raised dome piston which alters the flow as the transfer passes over it .Others use flat top pistons and have great success .So it just comes down to theory and experimentation .