Affordable home master solutions
A very common cause of failure to start the engine chainsaws or benzotrimmer, which few people pay attention to when starting up, is hidden in the processes taking place directly in the engine itself. When the engine fails to start after installing a new and fully functional carburetor on the engine, after replacing the piston rings, or after preventive maintenance, you should pay attention to the formation of the fuel-air mixture.
They say that a good knock on the engine itself comes out. But is it necessary to allow the engine to such a state when it is possible to prevent any “serious” malfunction in advance by identifying malfunctioning components and systems by the external signs of the engine that is still in operation?
A fresh, freshly purchased device is working properly, without jambs and for a long time. Over time, with an increase in the volume of the load, the engine will start not the same as before and there will be an assumption of weak fuel, soot in the cylinder and on the piston, weak compression. Of course, such and possible, other assumptions will be solid, since the term of the used chainsaw or benzotrimmer will be decently long.
In operation under load, such an engine will show good results compared to those that were in the first hours of operation after the acquisition. Fuel consumption will increase slightly, and the user will not attach importance to this. The engine will work without breakdowns until the next preventive maintenance.
When the crankshaft oil seals lose their properties and can no longer cope with their purpose, the observed picture in sufficient quantity will be determined by signs indicating their production or destruction.
The main task for the seals is to seal the crankcase cavity, the internal space, where in the corresponding periods of crankshaft rotation through the chamber purge gas distribution of the combustible mixture occurs.
When the piston moves to the spark plug, forming a combustion chamber in the cylinder, the finished air-fuel mixture enters the crankcase, due to the resulting vacuum, through the inlet channel. That is, at this moment, the incoming fuel mixture will fill the entire crankcase in the required volume. Simultaneously with filling the crankcase cavity with the mixture, a vacuum acts on the diaphragm of the carburetor fuel pump through the pulse channel, which pumps the fuel into the metering chamber of the carburetor.
When the piston moves from the spark plug, after the mixture is burned in the combustion chamber, an excess pressure is formed in the crankcase cavity, which allows purging through the bypass channels of the combustible mixture into the cavity of the piston chamber. The same excess pressure through the pulse channel will again be applied to the membrane of the carburetor fuel pump, which at this point in time will pump fuel into the pump chamber.
Even without taking into account the fact that such engines do not have stable idle speed, that part of the still unburned air-fuel mixture is thrown into the muffler, and part falls onto the carburetor air filter, good tightness of the crankcase cavity is necessary.
All processes occurring in the engine will be changed or broken, when the tightness of the crankcase cavity is broken even slightly. But also any processes or inappropriate engine operation can accelerate the wear of the stuffing box. Some external signs indicating a violation of the crankcase tightness may be similar to those that will be associated with other ongoing processes in a well-functioning engine.
You can pick up more signs that only tentatively indicate a particular malfunction of any engine assembly, and you can easily make a mistake in determining the location of the malfunction, only relying on the above examples. Additional confirmation will be an autopsy or partial disassembly of the engine. And before you take the key or screwdriver, you need to make sure the carburetor is correctly set, the tightness of the mating surfaces of the nodes, the integrity of the gaskets and much more.
Video: Gas Trimmer And Chainsaw Do Not Start
It is necessary to change bearings and gaskets on a chainsaw or gas trimmer.
If the crankshaft oil seals can no longer cope with their purpose, then an oil-based dirty coating will appear on the outer surface of the crankcase or the entire engine of the chainsaw or gas trimmer.
Stuffing box (rubber reinforced cuff for shafts) on the flywheel side of the engine is larger and wears out more often than the oil seal on the starter side, and therefore dirt will appear on the side of the flywheel of the engine. From the flow of blown air, oil will fall onto the hot ribs of the engine cylinder, in confirmation of which a corresponding burning smell will be felt.
For a normally working engine with nominal permissible values of the available total clearances, the optimal variable loads do not exceed the safety factor of the crankshaft and bearings. The engine has been running for quite some time.
Over time, long-term operation due to natural wear on the bearings increases both radial and axial clearance, which will lead to an increase in the working clearance of the bearing in operation. An imbalance will appear on the crankshaft, having a noticeable effect on the life of the seals, which will no longer cope with their purpose. The contact pressure exerted by the crankshaft necks on the thrust bearings has a variable value, since crankshaft The engine runs on torsion under the influence of variable torque.
over, during long-term operation, no matter how hard the user tries to protect the engine from dust, dirt will accumulate between the bearing and the oil seal, which will accelerate the wear of both the bearings and the oil seal. In addition, soot will appear in the working chamber, which is collected during the combustion of a dirty combustible mixture.
The air-fuel mixture distributed by the piston will not be held in the crankcase. In the piston chamber, this mixture will be supplied in insufficient volume. The engine will stop, and subsequently starting it will be impossible. over, at the moment the piston forms a vacuum in the crankcase cavity, additional air will enter through the worn oil seals, and the volume of the incoming air-fuel mixture from the carburetor will decrease.
Torn oil seal on a gas trimmer.
Crankshaft oil seal, it is a rubber reinforced cuff for shafts, has two edges that should fit the neck of the shaft tightly, and each edge has its purpose. The inner edge, it is also considered to be the working edge, is reinforced with a tightening spring with a certain stiffness. The outer edge of the stuffing box is not reinforced and prevents the space between the edges from outside the dirt, dust from getting into the working cavity of the stuffing box, acting as anther.
I believe that this edge is also working, especially since when a vacuum appears in the crankcase cavity, this edge to some extent prevents additional air from entering the crankcase cavity.
With prolonged use of a chainsaw or gas trimmer, without preventive maintenance, the material from which the oil seal is made will lose its elasticity and become brittle. The edge will crumble and the tightening spring will at best be thrown onto the neck of the shaft, or remain on the gland and tighten the neck of the shaft, forming deepening scratches on it, rendering the crankshaft unusable, which could still be "saved".
Even when a new oil seal is installed on the same crankshaft, the likelihood of its rapid wear will be confirmed by the vagaries of the engine. And if the seals are still installed on the shaft dry, then their quick wear is guaranteed. The engine speed at a chainsaw or petrol trimmer can reach 14,000 rpm.
At such revolutions, the gland edges rub against the surface of the shaft journal, their temperature rises, because of which the rubber shrinkage increases, followed by the loss of elasticity. It will be natural here that the stuffing box is nevertheless cooled by the air-fuel mixture, but still, with good sealing by the edges of the stuffing box, heating will be present.
Before installing the stuffing box in its seat, we lubricate the front and rear working surfaces of the inner edge with Litol-24 grease and slightly fill the space between the working edge and the inner surface of the outer edge of the boot. We apply grease from the front to the back facet, according to the outer diameter of the stuffing box.
Be sure to apply grease to the neck of the crankshaft as well. The grease must remain in the space between the edges of the stuffing box.
External application of grease will facilitate the installation of the gland, in addition, this grease will fill in small irregularities and surface roughness in the seat on the crankcase. Internal lubrication will reduce friction between the surface of the shaft journal and the lip seals in contact with it, greatly reducing wear on working surfaces.