How to Change a Crankshaft on a Chainsaw
All malfunctions of chainsaws can be divided into two main groups: malfunctions of the engine with all its components and systems (ignition, fuel supply system, cylinder-piston group, exhaust system) and malfunctions of other components (chain brake, lubrication system, clutch, tire, etc.).
- The engine will not start;
- Starts up, but stalls;
- does not develop power, i.e. normally works at idle, but stalls under load.
When repairing a chainsaw with your own hands, you need to act by exclusion. check alternately all possible causes of the malfunction, starting with those that take less time to check and eliminate (see here for the design and operation of a two-stroke engine).
Ignition system. Almost all types of engine malfunctions listed above can be caused by ignition system malfunctions. Therefore, when they occur, it makes sense to start troubleshooting with a candle. This is all the more justified because the state of the latter can provide useful information about the operation of the fuel system. So, if a problem occurs, you need to turn out the candle and inspect it.
The wire is disconnected, and the candle is twisted with a special key.
If the candle is dry, it means that the problem is most likely not in the ignition system, but in the fuel mixture not entering the cylinder. You can wrap the candle back and take up the fuel system. If the candle is heavily sprayed with the fuel mixture, then there is an excess of it. This may occur due to misregistration of the carburetor or violation of the rules for starting. The candle is wiped and dried, the cylinder is drained, cutting off the fuel supply and working as a starter. to vent the combustion chamber and remove excess fuel. Then set the candle in place and repeat the launch.
The presence of a large amount of black soot also indicates a malfunction in the fuel system.
The ratio between oil and gasoline in the mixture may be violated, the carburetor is not adjusted, or poor-quality oil is used. The candle is washed in gasoline, cleaned with a needle or an awl of carbon deposits, clean the electrodes with a fine sandpaper and put in place.
In all these cases, it is not superfluous to check the gap between the electrodes of the candle. Depending on its brand, it should be in the range of 0.5-0.65 mm. It is necessary to check the sealing gasket of the candle. If it is worn or damaged, the tightness of the combustion chamber may not be ensured, which leads to a decrease in compression in the cylinder and problems in the engine.
Even if in the case of checking the spark plug there is good reason to believe that the fault is in the fuel system, you need to check the spark plug for a spark. At least in order to be sure that everything is in order with this. For this:
- put on the spark plug cable;
- using pliers with insulated handles, apply thread or nut to the cylinder;
- pull the starter handle and look. there is a spark or not.
If there is no spark, you just need to replace the candle. If the new candle does not have a spark, it is necessary to check the condition of the high-voltage wire for an open and contact with the candle.
The reason for the absence of a spark can also be a faulty ignition module or a violation of the gap between it and the flywheel magnetic circuit. It should be 0.2 mm. Violation of the gap becomes especially likely if before that the saw was disassembled with the flywheel and the ignition module removed. The clearance is set using a 0.2 mm thick gasket placed between the flywheel boss and the ignition module. Defective ignition module must be replaced.
Having checked the ignition system in this way and not having detected a malfunction, we can proceed to the fuel mixture supply system.
Fuel supply system. If inspection of the spark plugs found that fuel does not enter the cylinder, you need to consider all the possible reasons for this. It could be:
- non-receipt of fuel from the tank due to a clogged hole in its cap (breather), while a vacuum is created in the tank that prevents fuel from flowing out;
- contamination of the fuel filter installed in the tank;
- not receipt or insufficient supply of fuel mixture from the carburetor to the cylinder.
To diagnose the first two reasons, it is enough to disconnect the fuel hose from the carburetor and see if fuel flows out of it or not. If it flows fully, the breather and filter can not be checked, if it does not or weakly flows, we can assume that the cause of the malfunction is found. The breather is cleaned with a needle. The fuel filter is removed through the filler hole of the empty fuel tank using a wire hook, together with a suction hose from which the filter is disconnected and cleaned or replaced with a new one. Chainsaw manufacturers recommend changing the fuel filter every 3 months.
Video: How to Change a Crankshaft on a Chainsaw
Insufficient intake of the fuel mixture from the carburetor into the cylinder or a violation of the correct ratio between fuel and air mixed in the carburetor can occur for several reasons: due to clogging of the air filter, unregulated carburetor, clogging of its channels or mesh filter.
As a rule, repairing chainsaws is not complete without cleaning the air filter, since it gets dirty quite quickly. When this happens, air intake to the carburetor decreases, the fuel mixture at the outlet of it turns out to be too enriched, which disrupts the normal operation of the engine. Carefully remove the dirty filter for cleaning so that dirt does not get into the carburetor. The filter should be cleaned or washed in water with some detergent, dried and installed again.
Carburetor misregistration is eliminated by its adjustment. This is usually done with three screws. maximum and minimum idle speed and propeller. Adjustment must be carried out in strict accordance with the instructions, non-observance of which can lead to engine damage. Some saw manufacturers leave only one adjusting screw (idle). to exclude unwanted interference by inexperienced users in the carburetor. For an example of adjusting the carburetor of a chainsaw, see the article Working with a chainsaw.
If the carburetor adjustment did not help, you need to clean its channels and filter mesh, and at the same time check the integrity of the membrane. Carburetor. one of the most complex chainsaw devices, so proceed with disassembling and cleaning it with a full understanding of the responsibility of this operation. It consists of many small parts that have the peculiarity of quietly popping out of their seats and irretrievably lost, so that, having disassembled this capricious device, you can not assemble it.
Below is a diagram of another carburetor chainsaw.
If there is no experience and self-confidence, it is better to entrust the repair of a chainsaw carburetor to a service center specialist. Sometimes for high-quality cleaning of the carburetor it is necessary to apply ultrasonic cleaning.
Muffler. Often the cause of engine malfunction, especially in the case when the engine is operating normally at low revs and stalls under load, becomes clogging of the silencer’s spark arrester, which prevents normal exhaust, from the combustion products. Repair in this case consists in removing the muffler, disassembling (if it is collapsible) and wet cleaning it from soot using detergents. The non-separable muffler is dried with a hairdryer after washing. Remember that soot contains substances that are carcinogens, and dry cleaning, which may cause inhalation, is unacceptable. When removing the muffler, the engine outlet is plugged with a clean rag.
One of the reasons a muffler may clog. this is the use of a fuel mixture with an excessive amount of oil (the amount of oil is more than recommended by the manufacturer), and the use of either non-suitable oil for two-stroke engines or low-quality oil.
Cylinder piston group. Malfunctions of the cylinder-piston group are the most serious. This is the deterioration of the cylinder and piston, scratches and seizures on their surface, wear or sinking in the grooves of the piston rings, wear of the crankshaft bearings. Most of these malfunctions lead to a drop in pressure in the cylinder and, as a consequence, to the inability to start the engine, or its inability to give full power. There are several ways to assess the status of a cylinder-piston group (CPG).
You can remove the muffler and look through the opened window, in which a part of the side surface of the cylinder is visible. Despite the limitations of the review, a general idea of the state of the CPG in this way can still be obtained.
It is useful to measure the compression in the engine, which is quite informative regarding the condition of the parts of the CPG. The operation is carried out using a compressor installed in the candle hole.
The crankshaft is rotated using an electric motor (drill) with a flexible shaft or manually by a starter, while controlling the pressure on the pressure gauge. The last for a workable chainsaw should be at least 8-9 atm (0.8-0.9 MPa). With its decrease, engine power also drops. At a pressure of 5 atm, the engine may perhaps work, but only at idle.
It is possible to accurately assess the state of the CPG only by completely disassembling the engine. disconnecting the crankcase from the cylinder and removing the piston. If the latter has scuffs, chips or deep scratches, it must be changed. In relation to the cylinder, when developing or damaging the surface, it is possible to squander it under the repair size. The cause of low compression may be wear and coking of the piston ring. The serviceable ring should be clean of carbon deposits, sit in the piston groove freely and firmly pressed against the inner surface of the cylinder.
Chain lubrication system
With a significant (small is considered normal) oil leakage, it is necessary to check the tightness of the connection of the tubes to the pump fittings. They may fall or crack. Violation of the tightness of the oil pipe, in addition to sagging, can lead to insufficient lubrication of the chain. The pump begins to suck in air, which affects its performance. The leak is eliminated by replacing the tubes or sealing them with sealant.
The most serious damage to the lubrication system are cracks in the oil pump housing. In this case, it will have to be replaced.
Replacing Wear Parts
If you do not replace the wearing parts in time, their excessive wear will adversely affect the other parts of the chainsaw. In particular, if you do not change the tire and the drive sprocket in time, increased vibration will adversely affect the crankshaft bearings. The maximum depth of the tooth teeth should be 0.5 mm. In practice, sprockets are often operated up to a wear depth of 1 mm or more. not suspecting that this leads to an increased load on the crankshaft bearings and their accelerated failure. When 3-4 chains are worn, it is necessary to change the tire itself, by this time its wear reaches its limit values.
The chainsaw tire wears out especially in the area most often cut, usually. this is the underside of the guide rail. For uniform wear, each time the chain is replaced, the tire must be turned 180 ° relative to the horizontal axis.
When installing a new chain, a new drive sprocket should be installed. Since under normal load the service life of the drive sprocket is twice as long as the service life of the chain, it is advisable to use one sprocket for alternating operation of two chains. Thanks to this, the sprocket and chains wear out almost simultaneously. If a new chain is placed on a worn sprocket, then the leading chain links wear out much faster. For cost-effective operation of the chainsaw, always spend together: one guide bar, two chain sprockets, four saw chains.