How to Put the Piston On a Motoblock

how set the piston at TDC on walk-behind tractor

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How to Put the Piston On a Motoblock

Motoblocks are generally reliable and stable devices. But with active use, they still break periodically. Malfunctions can affect even carefully thought-out motors.

How does it work?

To understand the breakdowns and eliminate them, it is important to understand how everything works in a normal situation. Let us dwell on models with internal combustion engines for greater simplicity. Previously, two-stroke motoblocks were found, but now they are increasingly being replaced by four-stroke counterparts. Diesel devices are also gaining popularity. As for the transmission, it can be performed in three different versions.

The traditional approach involves the use of a gear transmission. Despite a decent level of reliability, this device takes up a lot of space. The transmission of force takes place using either a cone or a cylinder. Light motoblocks are predominantly equipped with a gear-worm transmission. A typical operating principle of a motoblock controller contains:

  • device that monitors the number of revolutions;
  • traction connecting this unit to the throttle;
  • spring.

The control unit operates on the basis of pneumatic or mechanical coupling. "Pneumatics" means the presence of a kind of wing that responds to the speed of the air flow. Centrifugal options involve placing a special camshaft inside the crankcase. It is complemented by small weights and an easily moving stock. The thrust is made of wire, and the sensitivity of the spring determines how accurately the speed will be maintained.

The role of the gas distribution mechanism is to supply a mixture of fuel and air into the cylinder. But the same device also provides exhaust gas removal. To influence the compression ratio, a decompressor is used. Gasoline engines are necessarily equipped with carburetors responsible for the preparation of the fuel-air mixture. Regardless of the type of fuel, a starter plays an important role.

Necessary components

To assemble or disassemble the motor block engine, a smooth, well-lit area is required, where nothing will interfere with the work. They are looking for the same place for repairs. The installation kit for both imported and domestic walk-behind tractors includes:

  • nozzles;
  • head parts of blocks;
  • radiators;
  • carburetors.

Troubleshoot Launch Issues

Often, a motor block engine repair is needed due to the fact that this motor does not start. If this problem occurs after winter storage, you may suspect:

  • fuel or oil clogging with water;
  • oxidation of electrical contacts;
  • insulation damage;
  • the appearance of solid debris in the carburetor.

To prevent these violations, you must carefully inspect any connections before each start. Noticing the slightest clamp of the cable, especially its twisting, it is impossible to start the engine.

Even before the very first start-up, it is necessary to assess whether there is enough oil in the crankcase. With a lack of it, the rapid destruction of the piston group is likely. In less than a second, the cylinders are covered with burrs.

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In this case, a very serious repair will be required, and sometimes even the replacement of damaged parts. Sometimes instability in the functioning of the apparatus is provoked by the abandonment of the lubricant for the winter. If this is precisely the reason, in the first few moments after starting up, puffs of white smoke will fall from the exhaust pipe. Immediately after this, the power plant stalls.

Diesel motoblocks may also not start due to lack of oil. Only a few models are equipped with anti-drop systems. Most people will have to monitor the health of the walk-behind tractor on their own. It is also worth considering that failures occur due to the systematic use of inappropriate fuel. If the usual recommendations do not give much effect, you need to remove the candle and see if there are any oil stains.

Oil, especially soot, should be carefully cleaned. Then the candle must be dried. The cylinder is also required to dry. As a “drying”, a very simple technique is used: repeated sharp pulling out of the starter cable. Often the question arises: what to do if the walk-behind tractor does not start, while it smokes black smoke.

Usually such a manifestation shows that the engine is overfilled with gasoline. It is also worth worrying about damage to the piston group. If both assumptions turned out to be incorrect, you should contact the service center. Further attempts to fix the malfunctions on their own can aggravate the breakdown.

When violations are associated with a lack of fuel in the working chamber, the candle will be dry.

You can deal with such a problem if:

  • pour out the old fuel;
  • thoroughly wash the gas or diesel tank;
  • clean the air filter;
  • clean the fuel hose and nozzles with a jet of compressed air;
  • add fresh fuel;
  • After opening the fuel line, blow out the channel located in the gas tank cap.

Video: How to Put the Piston On a Motoblock


In some cases, the failure is due to the fact that gasoline got into the oil sump. Check if this problem exists, it is necessary after any adjustment, carburetor settings.

If fuel clogging occurs continuously, you need to look at the carburetor needle. It is likely that just this node has become a weak point. It is worth noting that sometimes the motor-block engine sometimes shoots at the muffler, and perhaps even with a flame.

The most likely cause is incomplete fuel combustion. It is provoked by:

  • passes in the ignition system;
  • excessively saturated fuel mixture;
  • unjustified heating of this mixture.

When the walk-behind tractor also does not want to act, interruptions in the ignition system must be sought thoughtfully and consistently. Examines magneto, caps, candles and high-voltage wires.

Of paramount importance is the search for even minor contaminants. If everything is clean, you need to inspect the contacts of the ignition wires. Next, they check the stability of the electrodes, measure the distance between them using a special probe.

Functional Failures

Quite often, among the malfunctions of the motor block engine, its unstable action appears. If the engine idles idly and stops trying to add gas, the reason is rooted in a lack of fuel. Clean the grids of the fuel tank, carburetor and pipeline tap. And when problems arise even at idle, it is advisable to check the centrifugal regulator. Often traction sticks there.

Suppose a walk-behind tractor simply slows down without jerking. In many cases, this is due to the use of improperly configured, inappropriate or simply very worn motors. But replacing the power plant is not always reasonable. Installing a better spark plug can help. It is also worthwhile to assume the appearance of malfunctions in the operation of the carburetor float in the high-voltage wire.

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If the motor-block engine knocks, it is required to examine the camshaft and crankshaft. It is there that there are mainly sources of extraneous sounds.

In all these situations, there is no special need to carry out major repairs. High-quality troubleshooting is very important. It’s pointless to try to increase compression in all any modern engines, anyway the decompressor will not allow it to be done.

Replacement and adjustment

Quite often, unfortunately, there is a need to completely change the motor on the walk-behind tractor. When choosing a replacement device, it is recommended to give preference to products of well-known companies. Traditional prejudices about the products of Chinese factories have long become irrelevant. To avoid overpayments, you need to carefully analyze how productive the power plant should be. Buying a too powerful unit is simply irrational.

Even if there is no talk of a complete replacement, it is important to know how to adjust the agricultural machinery engine. It is advisable to start disassembling only after flushing the motor and removing oil from it. Lubricant is poured out only with the engine warmed up after a short run. Next, it’s time to remove the fuel tank. Consistently removed:

  • fuel supply hose;
  • air filter;
  • screen covering the cylinder.

Then remove the crankshaft pulley. Following the pulley, it is required to remove the fan, reflectors, insulating flywheel casings. Unscrew the cover, removing the rings and coupling housings. When the washer is removed, you can press out the flywheel using a wooden block.

Now, having understood the flywheel, the cylinder cover, camshaft and cam follower are removed. Once access to the connecting rod is obtained, remove the oil sprinkler and locknut. After repairing and changing damaged parts, the engine is assembled in the reverse order. You should familiarize yourself with the scheme in advance, then there will be no errors.

Damaged valves for a petrol walk-behind tractor are replaced after removal:

  • gas tank;
  • the head of the cylinder block;
  • carburetor;
  • silencer;
  • boxes.

Often there is a need to replace the rings. But this should be done only in the process of a more serious repair. An isolated ring change is in itself irrational both economically and technically. In addition, a high-quality ring group usually has the same service life as the cylinder. Change them at the same time.

Installation on an elastic band is advisable if a Chinese motor is placed on domestic motoblocks. As a platform, rubber pads are often used. The parts of the front shock absorber from the car of the classical scheme are suitable as them. Along with the need to rearrange the individual parts of the motor-block engine, many people have a need to install an electric starter themselves. This starter will have to be correctly connected to the battery.

The crown is attached only to the removed flywheels. Pre-clean all interfering parts of the motor. To remove the flywheel in many cases, you can not do without a special key. A generator and its magnets are placed in the flywheel assembly. When the battery terminals and contacts are aligned, a trial run of the walk-behind tractor should be carried out.

Advice

In order to repair and set up a walk-behind tractor less often, it is necessary to protect the motor from falling. This is especially true for products with four-stroke engines. Their maximum slope during operation cannot exceed 25 degrees. For a long time, the unit cannot be tilted more than 15 degrees. Otherwise, you may be afraid that part of the engine will be deprived of lubrication. Soon she will fail.

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For the same reason, long-term idling of the walk-behind tractor is not recommended. Before starting work, you should always check whether there is enough fuel and lubricating oil. Change these fluids and even add them only when the motor is off.

Do not start the walk-behind tractor when the levers associated with the wheel drive are locked. The cold engine is started only after installing the carburetor air dampers in the closed position; Always use strictly recommended fuel.

Valves are adjusted using:

  • universal wrenches;
  • probes of various sizes;
  • flattened screwdrivers.

About the intricacies of repairing a Subaru ex21 engine for a walk-behind tractor "Neva" see further.

Faced with the fact that there is no normal manual for installing a kit with type-setting oil scraper rings. I decided to share and at the same time keep part of the information in this blog post. I didn’t take my photos, because and here everything is described in detail, and I have the rings of the same manufacturer.
And so, let’s start copying the context)))

". Next, you need to wear rings.

Rings took type SM, now they are called NPREurope. Oil scraper rings are type-setting.

Check the clearance in the locks inside the cylinders.

The clearance in the locks is normal. About 0.45mm compression, and 0.35mm type-setting oil scraper. In a previous post, I wrote that the gap in the scraper is very small and they need to be filed, but this is not so =). Having opened the ring to the sleeve, the gap became about 0.35. Assembled by a separator. So everything is ok.

Now directly put on the piston. You need to start with a separator, and then thin oil scraper. And only then the second compression and then the first compression.
But first you need to do the following.
A very important point! Which for some reason almost no where they describe. Not in the manuals, not with the instructions for the rings.
So that the motor does not consume oil with stacked rings, it is necessary that the rings correctly they needed to work to orient correctly on the pistons.
I will try to explain available =)

Need to pick up "noodles" and squeeze by docking the castle. Like this.

Next, you need to mark one of the sides, for example with a marker. I marked the convex side on all of the oil rings.
With respect to the piston, the rings should be oriented in this way.

Here is a schematic overlaid the picture for clarity.

After the typesetting rings are installed, the second compression rings are installed. They are cast-iron, very fragile, it is impossible to unclench strongly. they will burst. It works as a compression and partially as a scraper. To do this, they either have a groove or an edge cut at an angle. There is also an obligatory inscription "UP" or "TOP". It must be oriented to the piston bottom, towards the combustion chamber. For verification, you can still focus on the undercut. If the undercut is inner (in the inner diameter of the ring), then the undercut should look towards the combustion chamber with such a recess, if the undercut is in the outer diameter, then we orient it towards the crankcase with this side.

The upper ring is steel, I put the inscriptions up (they usually write a thread on the rings), although there is not much difference.

After the rings are dressed, they need to be rotated 180 degrees relative to each other. But not anyhow.
Oil-sealed typesetting relative to each other’s locks to 180g, and relative to the separator lock to 90g.
The locks of all rings cannot be oriented towards the refrigerator (towards the finger).