Care and Cleaning of Model Heli Engines
Recently after talking to others I became aware of misconceptions regarding this controversial subject. Our helicopter engines are very expensive so anything we can do to improve their longevity is a definite plus. One should consider the fuel being used and its properties. Alcohol by its very nature likes to absorb water from the atmosphere. That being said reinforces the basic need for after run oil, pinching off of the fuel line to run the engine dry of alcohol and draining the fuel cell after a days flying. We can minimize the damaging corrosive conditions inside our engines by doing so. Another property of our fuel is the oil content. Model engines run on a high oil content of about 20% oil in the fuel. This oil will leak out the exhaust flanges and partially evaporated fuel that spit out the carb will leave oil behind to stick to the engines external surface. With high operating temperatures this becomes baked on the engines external cooling surfaces. This provides a barrier against heat transfer or air cooling. So we should periodically clean the outside of our engines in the interest of a healthy cooling system. Coking or carbon buildup inside our engines occurs over the long term and can be the cause of poor performance along with elevated engine temperatures. It is kind of like a slow chain reaction…more heat and a more rapid build up of carbon and so on. Carbon build up in the exhaust port can restrict gas flow causing reduced power output with poor performance and higher than normal temperatures. The crown of the piston and the combustion chamber are also subject to coking. This can unknowingly increase the compression which may manifest itself in the form of preignition. Again poor running with higher temps will result. Some people think that it is good practice to clean the surface of the piston that is in contact with the cylinder of varnish. This is not a proper thing to do. Your engine at this stage in life is broken in and happy with its internal cylinder to piston clearances. This varnish has also filled in the microscopic pores in the pistons surface and aids in sealing compression. If you remove this good varnish your piston will fit loosely in the cylinder and we all know that the ABC engine configuration relies on a tight fitting piston for good compression. On an older ringed engine the removal of this good varnish may result in piston slap due to increased piston to cylinder clearance. As far as cleaning the internal engine of combustion by-products goes stick with cleaning the top of the piston, cylinder head , exhaust port, and ring grooves if the piston is so equipped.
In performing cleaning there are many ways which I leave to your imagination subject to the following conditions. Do not remove or scratch the metal and stay away from corrosive cleaners. If you must use such cleaners thoroughly remove them after use. After removing carbon flush out all the particles and oil everything to prevent corrosion. Make sure the piston is installed in the same position it was removed eg. the back side of the piston is still facing the rear engine cover. This is also a good time to inspect the crankshaft bearings for rust and the connecting rod for looseness. Long term storage of engines requires the preservation of the internal parts by means of a corrosion inhibiter. Select one that will not gum up or evaporate over time. Try light machine oil. Don’t use WD-40 as it is more of a cleaner/solvent than an oil and has limited staying power. Apply oil through the glow plug hole and in the carb opening then flip the engine over by hand to distribute the lubricant to the bearings. When this is completed install the glow plug , cover the inlet and exhaust to keep moisture out. In closing I’d like to say that if your engine works fine don’t take it apart just to clean the inside as a routine maintenance practice. Clean it when doing other maintenance if it is needed, such as an annual bearing replacement or inspections. With proper care and inspection an engine should last several years for the average sport flyer.