I'm a small engine mechanic who repairs Stihl equipment. At a recent service school the instructor showed a photo of a converted FS55 weed trimmer and commented, "This is NOT covered under Stihl warranty!" :-)

Stihl produces two different types of chainsaw engines. The homeowner grade stuff has the engine built separate from the main frame of the saw; the professional grade stuff has the engine and main housing all in one. Their weed trimers/brushcutters would probably be better bets for conversion than their saws due to weight considerations with the good saw engines. The new "4-Mix" four stroke/two stroke hybrid engines should make very good aircraft conversions, but I haven't gotten my hands on a good used one yet.

If you can find an eleven digit number on any part of your old chainsaw I can look it up and tell you what model it is, and whether it's current production. Contact me directly at [email protected]