These little motors are an ideal introduction for any budding IC engine enthusiast, young or old. Pretty rugged but very basic. Engineering wise they’re pretty rough but good enough to actually work.
Last year I was presented with a poorly Eachine 6 cc for improvement. The Rubber piston rings would only last a few days before being ripped to shreds. Upon closer inspection the Stainless Steel cylinder liner was just a bored hole and even though they had used a particularly slow feed rate you could detect the groove with your fingers. After around 15 minutes with my Delapena cylinder hone I achieved a near mirror shine and no more ragged up piston rings.
I then turned my attention to the main bearings. A pair of closed cup needle rollers. To work properly these are normally press fitted into the holes which ensures the correct inside diameter. I decided to change them for precision Oilite bushes. And removed around 0.3 of a mm of excess slack. The big end bearing is made from a couple of Brass halves in the traditional manner with no means of proper lubrication. I drilled a 3 mm hole from the back of the shell along the length of the conrod. A 1 mm hole through the back of the shell was drilled centrally to allow tle light oil held in the conrod to lubricate the big end journal.
My last improvement was to move the gudgeon pin back by around 6 mm reducing the compression ratio. I set the ignition timing to just, or about TDC.
The engine now ran much slower and more to the point, quieter. It still jumped forwards but I’m sure that if a decently made support plinth was made it would be near perfect.
A small sight feed lubricator and a couple of oil cups added a better look to the finished article.
Graham.
