To increase the power of the 125-cc motorcycle "Minsk", athletes and amateurs have developed many methods of forcing the engine. The efficiency (power gain) of each method directly depends on the complexity of the work performed. The simplest methods involve the use of common parts and no need to use any machine tools.
It is necessary
- - a set of files and files;
- - welding unit;
- - piston with rings;
- - carburetor K65I with an intake manifold from Izh Planeta
Make sure the engine is in good condition on the main bearings and oil seals. The crankshaft is in perfect condition. The piston you have purchased is factory made, with an intact ring of the correct shape and tight circlips.
Measure the bypass and crankcase passages in the cylinder. If there is a difference in their sizes, cut a gasket for the cylinder along the contours of the engine crankcase and attach it to the cylinder. Then, chamfer the channels 10 mm deep until they match the stencil made. Round off the chamfer corners with a radius of 3 mm.
File the inlet window so that it rises 1 mm. During the operation, make sure that the engine piston at its bottom dead center does not open this window with its upper edge.
Make grooves in the piston crown to improve the timing and heat dissipation of the engine. Make the grooves flat (and not round, like the piston crown) and arrange them symmetrically. They should reach almost to the center of the piston. Level the transitions with sandpaper.
Polish the piston rings with sandpaper on the inside, and also chamfer the inside radius at 0.25 width and 0.5 height. Shorten the piston skirt by 5 mm if you are not going to change the carburetor. If you plan to change the carburetor, shorten the skirt by 11 mm. At the same time, cut it off at an angle, and adjust the bypass ports in the piston to match the windows in the sleeve.
Plug the bottom ring groove on the piston. Next to the stopper and symmetrically on the other side, drill a recess with a diameter of 2 mm to a depth of 2 mm and press in an aluminum wire. Align the press-in place with a file. Polish the bottom of the piston to a mirror-like surface. Chamfer as little as possible around the entire circumference of the piston skirt.
Install the K65I carburetor with 32 mm jets and an intake manifold from the Izh Planet motorcycle. Shorten the collector from the cylinder side by 30% and grind the collector itself down to 24x34 mm. In this case, the carburetor installed on it should take a horizontal or slightly tilted position. Bend the studs to the required angle to secure the manifold to the cylinder. Then adjust the cylinder jacket in the intake port until it is in smooth alignment with the manifold.
When assembling the engine, discard the cylinder head gasket. Seal the flange with adhesive sealant and tighten with the carburetor without using excessive tightening forces. Install a 1980 muffler. It has a long, cigar-like appearance with a smooth taper at the end. When installing, bring it as close to the cylinder as possible, shortening the length of the exhaust manifold to a value of 300-350 mm. Remove the protruding horse muffler. Put the KAMAZ oil filter as an air filter.