How much compression should a chainsaw have?
Having read tips on the Internet about how to properly wind up a chainsaw, many people begin to spoil their machine, significantly reducing its service life.
What Compression in a Chainsaw
Not long ago, the engine was running like clockwork, but its output has dropped, fuel and oil consumption increased. Vibration is noticeable at idle speed. the engine is obviously “inebriated”, i.e.е. one of the cylinders is not working properly. And if changing the plugs will not change anything, in such cases, to determine the cause of the malfunction often resorted to measuring the compression. one of the easiest and most accessible ways to diagnose.
What Affects Compression?
Theoretically, the maximum cylinder pressure at the end of the compression stroke, when the piston is in its top dead center (TDC), depends on a number of factors. In terms of repair practice, they ultimately affect the amount of air that enters the cylinder. the higher it is, the higher the compression. First of all, you need to know the throttle position. covering or closing it, obviously, will greatly reduce the pressure in the cylinder. the amount of air is understandably affected by the degree of contamination of the air filter. Some mechanics make mistakes in timing, such as installing the timing belt or camshaft drive chain. This changes the timing of intake valve closure, shifting the onset of compression in the cylinder to one side or the other. Then the compression values will be different. Valve timing has a major impact on compression. Thus, a small gap in the intake valve actuator will lead to their later closing and, accordingly, to a decrease in compression. Simultaneously, a small gap in the exhaust valves increases the so-called valve overlap. the angle of rotation of the crankshaft, during which both valves in a cylinder are opened simultaneously. The result is the same.compression will be reduced. Engine temperature will also have an effect on compression. the smaller it is, the more the air compressed in the cylinder will be cooled and the less its pressure will be. By the way, the clearances in the valve train will also “follow” the temperature. the lower it is, the smaller the clearances and the less the compression.
- first of all let’s point out the temperature of the engine. it increases compression, as parts fit together better, taking dimensions and mutual position more in line with the working ones;
- it is then recalled that the oil that enters the combustion chamber through the valve guides, piston rings, crankcase ventilation system and turbocharger seals, significantly increases the compression, because it has a sealing effect;
- fuel entering the cylinder in the form of droplets, on the contrary, reduces compression, as it liquefies and washes oil from the parts and has no sealing effect due to low viscosity;
- leaky check valve or compressor hose and high spring force on the check valve will have the same effect;
- and finally, the higher the crankshaft RPM, the less leakage through the leaks, the higher the compression.
HOW to measure compression chainsaw 4500
on the Campion 254 chainsaw Video commentary forAnton Rogachev.
Compression Check on a chainsaw (For Anton Rogachev)
How to measure compression correctly?
If all the above factors are taken into account, the following simple rules should be observed when measuring compression:
- engine must be “warm”. fuel supply must be shut off. You can, for example, turn off the gas pump, nozzles or use other ways to prevent large quantities of fuel from entering the cylinders;
- All spark plugs must be removed. Selective dismantling of plugs, practiced at some service stations, is unacceptable because it increases the resistance to rotation and reduces the engine speed arbitrarily when cranking the starter;
- the battery must be fully charged, and the starter. is defective.
Compression is measured with both open and closed throttle. Each of the methods gives different results and allows you to identify different defects. So, when the choke is closed, obviously little air will enter the cylinders, so the compression will be low and be about 0.6-0.8 MPa. The air leakage in this case is comparable with that of the cylinder. The consequence is that the compression is particularly susceptible to leakage. even for small leaks its value drops by several times. This assumption allows conclusions or assumptions about the following engine defects: Valve to seat fit not fully satisfactory; valve hang-up, e. g., due to faulty assembly of the hydraulic tappets mechanism; cam profile defects in camshaft designs with hydraulic tappets, including uneven wear or runout on the cam back; leakage caused by burnout of the head gasket or a crack in the combustion chamber wall. When measuring compression with the choke open the picture will be different. Large amounts of incoming air and increased pressure in the cylinder, of course, contribute to increased leakage. However, they are obviously less than the air supply. As a consequence, the compression does not drop that much (to about 0.8-0.9 MPa). So the way of measurement with an open shutter is better suited to determine more “rough” defects of the engine, such as breakages and blowouts of pistons, breakages or hang-up (shrouded) of rings in the piston grooves, deformation or blowouts of valves, serious damage (scuffing) of the cylinder surface. In both methods of measurement, it is desirable to consider the dynamics of pressure build-up. This will help determine the true nature of the fault more accurately. So, if at the first stroke the value of pressure measured with a compressometer is low (0.3-0.4 MPa), and at the subsequent strokes the pressure rises sharply. it indirectly indicates the wear of piston rings. In that case, pouring a small amount of oil into the cylinder (3-5 cc of oil in the cylinder) would be the best way to change the sprocket.The longer the cylinder and piston group, the higher the compression in the cylinder block. If, on the other hand, the pressure during the first cycle is as high as 0,7-0,9 MPa and then hardly rises during the following cycle, a leaky valve or head gasket is more likely. Of course, the cause can be determined more accurately using other diagnostic tools.
Chainsaw design and general fault classification
The prerequisite for a successful repair is correct diagnosis. Therefore, to determine why the chainsaw has failed and, most importantly, how to make it work again, first of all, it is necessary to know the features of its design.
It should be noted, it is not particularly difficult, as it includes:
- The engine (two-stroke gasoline engine);
- The functional part (the saw bar and the chain);
- systems that ensure that the two units work together (ignition, filtration, lubrication, etc.).д.), i.e. the instrument as a whole.
In order to simplify the diagnostics of faults, they are usually divided into two main categories:
Most often failures occur in the engine systems, but the other parts of the tool due to intensive use or improper maintenance can at any time break down. So how to determine where exactly the fault occurred? A simple logic will help us in this.
If the problem is in the engine, it will be:
As for all the other faults, as a rule, they occur during the normal operation of the motor.
Malfunctions of Chinese chainsaws: an overview of popular ones and their solutions
Buy a cheap chainsaw made in China is not particularly difficult: in markets, construction hypermarkets and online stores there is a huge number of benzoinstrument from the Celestial Empire. However, the low price almost always hides poor quality.
Among the most popular faults of Chinese chain saws should be listed:
- Lubrication system does not work properly. Clogged oil ducts are cleaned, and if the oil pump failed, it is necessary to replace.
- The starter rope breaks.
- Breakage of the plastic starter shaft. It can be replaced with a simple metal bolt.
In the case of the slightest suspicion of improper operation of the chainsaw, it is worth immediately making a complete diagnosis of the tool. Only with proper use and timely maintenance can you count on a chainsaw lasting a long time.
Almost every villager or dacha owner has a chainsaw these days. They are in high demand, because they are quite easy to work with. Even if broken, the saw can be repaired with their own hands, although it may take a long time. In the economy, consumers use household or semi-professional (farm) saws, which are designed for a small front of work.
What is needed to change the sprocket on a chainsaw?
The main thing that is required is an understanding of the inner workings of the saw and a certain knack: if you are holding this power tool in your hands for the first time, it is better not to experiment with repairs and leave it to more experienced people.
If you are confident in your own technical competence, replacing the sprocket on your chainsaw will require:
No Spark in a Chainsaw Causes AURAMM.RU
Our client still malfunctions chainsaws are divided into two main groups: problems with the motor with its complete nodes are not systems (ignition, fuel supply system, the cylinder-piston group, the exhaust system) and other nodes (chain brake, lubrication system, clutch, tire, etc.) are not faulty.).
Let’s move specifically to the main ignition components of the gearless chainsaw. Let me list the parts of the ignition system:
- Flywheel with magnets (magneto)
- The ignition module
- Glow plug
- Armored wire (high voltage wire)
- Closing (on-off) wires
Here I call the flywheel a magneto. In fact, magneto, this is the general title of the entire alternator, not directly the flywheel with magnets. So don’t emphasize my habit of naming, in this case, “things by other names.”).
What is the flywheel? For beginners I will explain that visually it reminds a giant (specifically in a chainsaw) duralumin fan gear, the blades of which, when rotating, play a role first of cooling the motor. The flywheel is installed on the left side of the chainsaw, behind the starter cover. The flywheel is mounted by mounting it on the crankshaft with a key and two pins. There is a thread on the end of the shaft to secure the flywheel with a nut. This nut needs to be tightened firmly when installing the flywheel, otherwise it may cut the key, which prevents free running. By the way, the key is placed on the crankshaft so that when the magnets correlate with the ignition module core, the piston was at the proper level (top dead center) to cut the spark and ignite the fuel.
At the end of the flywheel, in the middle of the blades, there are powerful magnets with different polarities “north-south. Usually two magnets are installed, but on some chainsaw models there may be more. Opposite to them on the other side of the flywheel are installed counterweights, for uniform rotation.
Powerful magnets with different polarities “north-south”, which make a magnetic field when the flywheel rotates
Next to the magneto (flywheel) at a certain distance (gap) is installed ignition module (coil with an electric board in a polymer or textolite “jacket” on a laminated iron core, which also serves as the attachment to the body of the saw). The ignition module can be installed on different sides. to the right of the magneto (flywheel), on the left or on top. depending on the model of the chainsaw.
Husqvarna ignition module with high-voltage wire
From the module (coil) go the on-off wires (breaker) and the cable (armor wire), mounted in the cap, where the glow plug is inserted. Plug wires have a small cross section unlike a spark plug cable which carries high voltage. The spark plug has a side and center electrode, a body and an insulator, respectively. The spark plug is screwed into the cylinder head and transmits a spark to ignite the fuel mixture in the engine.
Chain Lube System
If there is significant (a small amount is considered normal) leakage of oil check the tightness of connections of pipes to pump fittings. They may be loose or cracked. A leaking oil pipe can cause not only leaks but also inadequate lubrication of the chain. Pump begins to suck air, which affects its performance. No spark on chainsaw | video in Zaporozhsky. Leakage can be eliminated by replacing the tubes or by sealing them with sealant.
READ How to Change a Piston on a STIHL 180 Video
The most serious breakdown of the lubrication system are cracks in the oil pump housing. In this case, it will have to be replaced.
NO SPARK IN THE CHAINSAW, ignition coil replacement
This video examines ignition coil failure, its replacement and starting the chainsaw. Also watch my.
An insufficient flow of fuel mixture from the carburettor into the cylinder or a disturbance in the correct ratio between fuel and air mixed in the carburettor may be due to several causes: a clogged air filter, a non-adjusted carburettor, clogged carburettor ports or a clogged filter screen.
As a rule, the repair of chain saws does not do without cleaning the air filter, because it gets dirty pretty quickly. When this happens, the air flow into the carburetor is reduced, the fuel mixture at the outlet of it gets too enriched, which violates the normal operation of the engine. Remove the dirty filter for cleaning carefully, so that dirt from it does not get into the carburetor. Clean or flush the filter with water and some detergent, then dry it and put it back.
The carburetor is adjusted if it is out of adjustment. This is usually done with three screws. maximum and minimum revolutions and the idle speed screw. Adjustment should be performed in strict accordance with the instructions, failure to comply with which can lead to engine damage. Some saw manufacturers leave only one adjustment screw (idle speed). to prevent unwanted interference by inexperienced users with the carburetor. No spark on chainsaw no sparks chainsaw. YouTube. For an example of adjusting a chainsaw carburetor, see Working with a Chainsaw.
If adjusting carburetor didn’t help, clean carburetor passages and filter screen, and check for continuity of carburetor diaphragm. The carburetor is one of the most complex devices of a chainsaw, so proceed to its disassembly and cleaning should be fully aware of the responsibility of this operation. It consists of many small parts that tend to pop out of their places unnoticed and get lost forever, so that if you disassemble this capricious device you might not be able to reassemble it.
Below is a diagram of another chainsaw carburetor.
If you lack experience and confidence in your own strength, it is better to entrust the repair of the carburetor chain saw to a specialist service center. Sometimes good carburetor cleaning requires the use of ultrasonic cleaning.
Muffler. why there is no spark on the chainsaw? Find out the answer for free from the experts! It is not uncommon for the cause of engine failure, especially when the engine is running normally at low RPM and stalls under load, to be clogged with combustion products of the muffler spark arrestor, which prevents normal exhaust. Repair in this case consists of removing the muffler, disassembly (if it is demountable) and its wet cleaning from carbon deposits with detergents. The non-disassembled muffler can be dried with a hair dryer after the wash. Remember that soot contains substances that are carcinogens, and dry cleaning, due to which you can inhale them, is unacceptable. When removing the muffler, the engine exhaust port is plugged with a clean rag.
What to flush the carburetor of a chainsaw?
To clean the node from strong contaminants, it is best to use a product that comes on sale in pressurized cylinders. The cleaner comes with a dispenser and a long thin tube, which allows you to spray in all hard-to-reach places.
Remember that the carburetor on a chain saw is cleaned with flammable chemicals. Work with them must be in a special protective mask and only in well-ventilated rooms.
Read also: How to bend the muffler pipe with his hands
To clean the carburetor on the chainsaw, the unit will need to be partially disassembled. The throttle, adjustment screws, carburetor body, and other carburetor parts will need to be washed with canister cleaner and set aside until completely dry. Once all the elements are dry, the assembly can be assembled and put back on the chainsaw.
What to do if the chainsaw doesn’t brake?
The opposite of the previous situation, where the gas tool reaches high power very quickly and does not brake it. At the same time, you can see that this can not be eliminated in any way, neither by screwing on the body, nor by cleaning the carburetor. It would seem that what more do you need, the saw works, gives power as instructed. But the trouble is that in this case you need ten times more fuel than usual.
The following steps may help:
- Check the gas cable;
- Inspection of the return spring, which may have just come off;
- Seal the rear valve, which must be very tightly closed.
Usually one of these events can make a lot of sense.
Another technical problem is the situation when the chainsaw itself picks up speed, which is usually not the only reason. In this case, the saw may periodically stagnate under load, preventing it from being fully used for its intended purpose.
The main causes may be:
- A clogged carburetor or fuel/air filter;
- The integrity of the fuel supply hose is compromised;
- Leaks in the supply line from the carburetor to the engine cylinder;
- Once again, one of the screws (usually the G screw) of the carburetor system is improperly installed.
Therefore, the easiest thing you can do at home is to clean the carburetor and filters, both air and fuel. It is important to maintain proper adjustment of the L and H screw elements at the same time. Some people advise to completely remove the fuel filter from the stock, but this is not an option, because the carburetor will not last that long.
So before you get started, you just need to see if it sinks, if there are any bends in the hoses that the fuel flows through, and then it will be taken for more drastic action.
As you can see, there are many problems, but a great panacea for each of them is a timely diagnosis, which can answer many questions about the technical failure of the device before it appears.