Rebuilding a 300 Hirth into a MOD motor
The PTO side. There is a lot of carbon build up on the piston and the rings are partially stuck. * * * The PTO side seal plate and gasket. The MAG side gasket was missing so one will have to be made.
A little hard to see, but the PTO bearing is rusty. Both crank bearings will be replaced. * * * This is the MAG side seal plate. Note the relief machined into the upper left portion. This was done to allow more room for the stator wires (points/ground/lighting). Also note the longer screw on the far right. This will go in the damaged hole as there are good threads farther down, and a thread insert will not be needed.
Here is the clutch taper with the stub cut off and the hole drilled and tapped. Now I can use a Salsbury clutch which is correct for the '69 Arctic MOD. * * * Here was another problem; it's hard to see, but the PTO seal was put in backwards. New seals will be installed and will be installed correctly... LOL!.
Here is another view of the PTO seal. The backwards seal most likely contributed to the oil and dirt build up on this side. * * * Here is the crank all cleaned up and ready to go. The rod clearences were within spec and the runout was okay, too.
The flywheel all cleaned up and ready to rock. And yes, cleaning out the oil and dirt from all those enclosed cooling fins was a bit of a chore... * * * The new NTN crank bearings.
Here is the air shroud that needed to be trimmed. Here you can see what it looked like before, with the cut piece set back in place. * * * Here you can see it trimmed and how much was taken off. Trimming was done with a fine tooth hacksaw and smoothed with a die grinder.
* * * 
* * * 
* * * 
* * * 
* * * 
* * * 