To the best of my knowledge there are non of the 4 cycle "micro" engines that have oil filters. The small Hondas and Robin Subarus don't have an oil filter and, of course, 2 cycles engines may have a fuel filter that would also filter the oil mixed in the gas. The Subaru-Robin EHO 35s I used to run carried only 80-100mL of oil and I changed it very often, because there was no filter and only 2 quarts of oil would last more than an entire year. Change the oil often and it shouldn't be an issue. Remember, these little engines don't have a regular oil pump, so there is no simple effective way to put a filter into the system. Most use a pulse from the piston moving down the cylinder to "pump" oil in a mist around the crankcase, onto the cylinder/bottom of the piston, and up into the vavle train over the cylinder. It sounds sort of goofy and primitive and quite ineffective, but it works very well and has proven over time to be effective.