Adjustment of valves on the moped "Alpha". Moped "Alpha" - photo, characteristics

Why do I need to adjust the valves on the moped "Alpha"? The moped engine FMB 139 is equipped with a gas distribution mechanism with a camshaft in the cylinder head. The valves are driven by rocker arms. During engine operation, the valves undergo thermal expansion, so there is a small gap between the rocker and the valve, which compensates for the thermal expansion. If there is insufficient or excessive clearance, serious engine damage may occur. The negative effect of incorrect gaps accumulates gradually and can cause burn-out of valves, destruction of the saddle, reduction of compression, overheating and deformation of important timing components. Adjustment of valves on the moped "Alpha" should be performed several times per season. If the thermal gaps are incorrectly adjusted, a characteristic knocking sound may appear when the engine is running, which is also the reason for adjusting the valves.

The motor of the moped "Alpha" FMB 139

The four-stroke engine FMB 139 is one of the main advantages of the moped "Alpha". Photo of the engine is presented above. This is a very reliable and economical small mass engine. Its volume can vary from 49 to 125 cm., And the power can be from 5 to 8 hp. Modifications to this engine may have a different cylinder volume. It is possible to install a more or less powerful version of the cylinder-piston group at home. The engine is equipped with a four-speed gearbox. Above it is located carburetor moped "Alpha".

Gas distribution mechanism engine FMB 139

The engine timing system FMB 139 is equipped with a camshaft located in the cylinder head. The valves are vertically and V-shaped and driven by a rocker arm, which in turn is driven by camshaft cams. This system is very similar to the timing of the Moskvich 412, only one cylinder, and two valves.

The camshaft is driven by a chain drive. It, in turn, is driven by a gear, located on the axis of the rotor of the generator, which is the axis of rotation of the crankshaft.

The prevention of the timing and the consequences of its breakdown

All the timing elements of the engine FMB 139 require a periodic and constant inspection of the degree of their wear and tear. The stretching of the timing chain and the wear of the tension elements can lead to its breakage, which will require enough troublesome repair, associated with the need to remove the generator rotor, or dismantling the entire crankcase to replace the oil pump gear. In addition, an open timing chain can cause deformation of the valves, which will require their replacement and grinding to the saddle plates of new valves. The failure of individual elements of the timing can cause a number of other serious failures.

Symptoms of incorrect valve settings

If the thermal clearances are too large, this can cause a characteristic knock or ringing that occurs when the engine is running. Loss of compression can also be an indirect consequence of improper valve settings. Indirect consequences of improper adjustment of valves can be an increase in fuel consumption with a decrease in power due to depressurization of the valves, as well as loss of synchronization of their operation, when the work of the valves begins to outrun or lag behind the cycles of the piston.

The arrangement of valves and their lapping

The valve on the moped "Alpha" is made according to the same scheme as for the car. They have a plate and rod, which lengthens due to thermal expansion when the engine is running. The normal size of the gap should be 0.05 mm. When the valves are heated, the thermal gap almost completely disappears. Plates of valves sealed in the seat sealed, and their edges should be perfectly attached to the edges of the saddle. Lapping of valves on a moped is no different from a similar operation for car engines and is done with the same paste by hand, or mechanically with a drill. To remove the valves from the cylinder head FMB 139 uses a special tubular puller.

Negative consequences arising from improper adjustment of valves

The pusher on the rocker should press the valve, but as the thermal gap increases, it begins to hit the valve, which causes a characteristic ringing noise during engine operation. This can lead to an acceleration of wear of the most important engine components. The valve plate begins to beat more strongly on the seat, which causes defects on the edge of the seat and the valve. In conditions of high temperatures, the edges of the edges in the places of small deformations begin to burn, they cease to adhere tightly to each other. The leakage is lost, the burning products of combustion break through the valve and destroy the surface of the edges even more. There is overheating of the valve, and in some cases, the seat and the valve, and the valve itself, which fragments enter the combustion chamber, scratching the piston and cylinder walls begin to crumble.

In the absence of a thermal gap, the exhaust valve first suffers. The cycle of his work is stretched, which leads to overheating and melting of its edges. If the valve is tightened, it can generally cease to close. During operation, an increase in the dimensions of the thermal gap usually occurs, which is the reason for the need for regular checks of this quantity.

Adjustment of valves on the moped "Alpha"

Valves on the engine FMB 139 are located on the top and bottom of the cylinder head. To reach them, you need to unscrew the covers. Adjusting the valves on the moped does not require removing the entire head. But you need to put the cylinder in a dead spot. To do this, on the top cover of the generator rotor there is an opening, closed, in turn, with a plastic cover. After having unscrewed it, you can see the case of the generator, on which marks are placed. With the kick-starter, you can gently rotate the rotor of the generator until the "T" mark appears. The same operation can be performed using the wheel. Moped should be put on the central step, turn on the fourth gear and gently rotate the wheel until the sight hole shows the "T" mark.

In order to precisely control this process, it is possible to remove the cover from the timing block of the timing star located on the left side of the cylinder head. This star has a mark in the form of a dot. If this label is in the extreme left position, then this will mean a dead point. After installing the cylinder in a dead center, the valves on the moped "Alpha" can be adjusted. It is necessary to loosen the fixing nut and pusher. Then you need to push the 0.05 mm probe between the pusher and the valve stem, manually tighten the pusher, but so that the probe can be removed. Then the position of the pusher needs to be fastened with a fixing nut.