We have done the piston cylinder change mode on several bikes, and we still had blow-by which is the cause of the oil propogation. The true fix is to better vent the crank-case. Changing the pistons and cylinders does not solve the problem in all casees. Let me explain to you the problem, you have a very over-square piston 100mm bore by 62mm stroke, at high RPM you have some level of piston rock, and ring flutter. This causes some of the compression mixture to leak past the piston/rings and pressurize the crank case. At high RPM and oil temperature you start transporting oil through the vent. The return hole in the vent is to small to allow all the oil to return it is transported up the vent into the air-box. We have tried and experimanted with many fixes pistons-cylinders, pistal- pistons, etc the best fix is to modify the breather as I previously stated. We do leak down tests on the engines both cold and hot and the engines are tight, good ring seal, the problem is not ring seal or cylinder wear, it is caused by piston rock and ring flutter. The new engines with the deep sump will be much less prone to have this problem. Fix the vent if you need conformation and don't belive me ask someone who knows Ducs, I would try Bruce at BCM or John Hacket at JHP, I have discussed this problem with both of them on several occasions.
