Portable tools such as chain saws or power cutters are used in many different handling positions, even up side down. They are therefore usually crankcase scavenged and lubricant, e.g., oil is supplied to the crankcase. This lubrication system works in every handling position.
However, oil tends to collect in the crankcase so there is a surplus in the crankcase and tends to be a shortage for some lubricating places. By adding more oil this can of course be compensated for, but this will increase oil consumption and increase emissions of oil smoke in the exhaust gases.
There are even lubricating places that are very difficult to lubricate at all, e.g., a bearing on the crankshaft supporting a centrifugal clutch normally used for portable tools. Some tools use a sealed bearing that is pre-filled with grease.
The seals will wear resulting in loss of grease and the shaft will corrode increasing the wear of the seals and the loss of grease and shortening the life of the bearing.
Other tools use a duct arranged in the crankshaft so that one end of the duct reaches the bearing area. The other end of the duct either ends in the crankcase to get oilmist there, or ends in the outer end of the crankshaft to be lubricated with grease occasionally. In both cases the efficiency is limited and also dirt easily fills the respective duct so that the lubrication will be decreased or stopped.