ORIGINAL: pe reivers
Of engines, we have two kinds.
1)Engines with bearings at both sides of the crank. like most garden and chain saw engines, Zenoah, 3W etc.
These engines have the cylinder at exactly right angles to the crankshaft, and the conrod big end can take quite high specific loads before things get hairy.
2) Engines with cantilever cranks, like DA, MVVS, Roto. In order to keep the conrod on the crankpin, the cylinder centerline is slightly rotated towards the engine rear, about 1/2 degree. Because now the connecting rod sits at an angle of 90.5 degees to the crankpin, the roller needles are loaded on their edges, and need much more viscosity in the oil, or the oil film will break. At the highest combustion pressures, the crank will bend slightly and improve the needle load distribution, but stil..
pe,
Thanks for taking the time explain the differences in the crank designs, and what it means in relation to the oils we use. I wasn't aware that the synthetic oils had that much higher of a flash point. Granted you shouldn't need it, but it's a nice insurance policy to have.
It sounds as if the cantilever crank engines are more critical of the oil used. Isn't ZDZ recommending the Pennzoil petroleum based oils?