How to assemble a gearbox of a power tiller correctly

Hodoumenshchitel for power tiller with his hands, drawings

Correctly and thoroughly cultivated soil is the key to a good harvest. That’s why equipment like the power tiller is so common in agriculture. It is used to loosen the ground, mainly for cultivating the soil before sowing. With a cultivator, the use of a shovel recedes into the background, as it greatly reduces the use of physical force and facilitates work on a piece of land.

Cultivator’s functionality is not limited to loosening. It is a handy and maneuverable device that plows, cuts furrows, breaks breasts, destroys weeds in between the rows, dips crops, digs up root crops, fertilizes the soil with mineral salts or organic compost.

But such a multifunctional machine also costs a certain amount of money. So it is unlikely that someone wants to buy a cultivator, and after a few days of work to break a cutter or break the engine. And it happens, and quite often. And the reason is not a factory defect or low-quality and unreliable device, but that you do not follow the rules of operation and care for him.

To avoid trouble and wasting money on repairs, you need to be familiar with the cultivator, its types, and ways of operation and maintenance. Before understanding the rules of care for the cultivator, it is not superfluous to know some more important points in its use.

What are the damages??

Most of the problems in the gearbox of a power tiller are caused by overloading. Such failures include bursting of bushings on metal chain, which leads to so-called “slippage. Also, owners of motor blocks very often find broken bushings shifting gears. To avoid such troubles, seasoned owners advise to switch gears only when the machine is at a complete standstill, in no case while running. In addition, a common phenomenon is considered to be the breakage of the sprocket. That is, the factory welding is not enough for the star to withstand overloading.

“Get out” of this unfortunate situation is very simple, you just need to return the sprocket to its original position and tack weld it much better. Lateral loads lead to wear of the thrust washer, after which a runoff of bushings from the chain is observed. In addition to all of the above, it is necessary to periodically check the oil level in the gearbox, as well as to replace it.

Power tillers with pinion gears and reduction gears for power tillers

The reduction gearbox for pulling tractors, or in common parlance a speed reducer, is mounted on modern, air-cooled diesel and gasoline power tillers. That allows the user to use the single-axle tractor on particularly heavy soils for plowing and digging potatoes. The reduction gearbox helps when the wheels slip, when not enough own power.

Power tillers with a pinion gearbox

To understand what a gear reducer is, consider the structure of the transmission. It transmits torque from the engine to the wheels, and changes the speed and direction of the power tiller. Transmission consists of gearbox, differential, gearbox and clutch. Transmission units can be pinion, chain, belt or a combination of both. Gear transmission consists of conical and spur gears (gearbox). It is used on some models of machines and heavy motor blocks. In the picture you can see the gear transmission of “Ugra” NMB-1 power tiller, which uses a pinion gearbox.

The process of making a gearbox

First the powertrain parameters are calculated. The number of revolutions of the crankshaft can be found in the technical specifications.

This is the first value required to perform the calculation. This value is not constant, with the addition of gas the number of revolutions increases. Base value: idle speed 10%.

Further, we calculate the revolutions of the axles of suspension. Knowing the wheel dimensions, it is possible to calculate the overrun per revolution. Calculate the number of axle revolutions for a comfortable speed. 3-5 km / h, which is the second value for the design.

For example, an idle speed of 10% is 600 rpm./min. Required wheel axle speed for 3 km/h is 200 rpm./min. So, the gear ratio should be 3:1. Axle speed is tripled in relation to engine shaft speed and torque is tripled accordingly. Gearbox types:

• Gears. uses the ratio of the number of teeth of the driven to the driven gears. The device works according to the principle of steam in a gearbox. Irrespective of the shape of the gears. teeth can be straight or beveled. Bevel gears are used when an angular gearbox is needed for a power tiller. Depends on the position of the motor. If the alignment between the motor shaft and the wheels is ensured, the angle is not needed.
• A worm drive is needed to create a large gear ratio when there is a large difference between the speed of the drive axle and the motor. This design is more difficult to make and maintain. This solution is optimal if the motor shaft is perpendicular to the wheel axle.
• Chain reducers work on the bicycle principle, but vice versa. The smaller sprocket is the master sprocket. Construction reliability is determined by the quality of the gear metal and the strength of the chain. A simple set from a bicycle may not hold the load, so stronger ones are used. motorcycle ones.
• Belt drives are the easiest to make. They are also the most unreliable and weakest. High torque may not be transmitted because the belts will slip. But there is less shock load on the motor. the design is gentler on the drive shaft, the jerk is smoothed out. Creep eliminates slippage by fitting a toothed belt. In this case, you need to find a pair of toothed pulleys, for example, from an automobile timing system.
• Combination system. A device with chain and pinion gears, can be made in one case, although the calculations in this case are more complicated. It is possible to transmit a huge torque at low motor power.

When choosing any design, do not forget the following rules:

Any device, except the belt, needs to be lubricated constantly, so it must be in a box. Sealed housing protects against dirt and dust, which are unavoidable in the field. Glands are installed on the shafts.

As an example, you can take factory products for Soviet agricultural machinery. Chain drives are not as sensitive to lubrication, but the chain must be cleaned and lubricated regularly.

Finishing off an off-the-shelf design

It is possible to select a suitably sized housing at a junkyard of old machinery, drill holes in the bearings for the shafts and assemble the device no worse than the factory one! Practice shows that the selection of prefabricated designs with minor modifications is much more efficient.

As an example we use a self-made block, based on the engine of an IZh motorcycle. A “native” gearbox with the ability to shift gears is used. It lacks the original gear ratio, but a small star on the output shaft of the gearbox with a large star from the drive wheel, provides already a good reduction in rpm.

Another small sprocket is put on the shaft, which is installed in the bearing pedestal, which transmits the torque to the wheels with a second chain. The drive axle, in turn, has a large-diameter sprocket. The end result is a design with 2-speed reduction and high torque.

Using a gearbox from a motorcycle, you can pick up the necessary speed of movement, almost without using the throttle grip. Almost always the motor runs at idle speed, which prolongs its life.

No less popular is a ready-made gearbox from a scooter “Muravey”. It is not necessary to use the wheel platform as a whole, it is enough to install on the axle of your rollers. Using the gearbox from the selected engine, you will get the best ratio of speed and power.

How to make a homemade gearbox for a power tiller

To assemble the converting device on a single axle tractor yourself, it is necessary to have the following tools:

• A caliper and a metal ruler;
• A set of screwdrivers of different sizes, including an oblique screwdriver;
• Pliers and wire cutters;
• Metal saw;
• an electric drill with a set of metal drills;
• vise;
• hammers. big and small;
• rubber pads.

If you decide to build your own gearbox for your power tiller, be sure to do a rough calculation. This will help you determine, at a minimum, the gear ratio and the type of converter you need.

Also with the help of preliminary calculations you will be able to estimate the dimensions of the future gear.

To make the correct calculation, determine the parameters of your engine. For the calculations, a few details need to be clarified:

• Number of revolutions of the engine crankshaft. But this value is not constant: just “pull up the throttle” and it will increase dramatically. That’s why the calculation is based on the base. the number of idle revolutions plus 10%.
• The calculated number of revolutions for the suspension axle. This is calculated using the diameter of the wheels to determine the coasting per full revolution. Based on this, you can calculate at what speed the axle should rotate in order to provide the most comfortable speed of your power tiller. This is an average of 3 to 5 km/h.

Let’s take a simple example: engine idle speed with 10% increase is 600 rpm, and it needs 200 rpm to achieve 3 km/h. Therefore, the estimated gear ratio is 3:1. In other words, to reduce the speed of the axle in three times, to provide a speed of 3 km per hour, three times the torque.

Step-by-step instructions for assembling a chain reducer

If you have some skills, you can make a reducer of any type with your own hands, but the easiest way to assemble a small-sized mechanism with a chain gear. the materials for it are easier to find and more reliable in operation.

To make a homemade chain mechanism, stock up on the following parts and materials

• sprockets with the required number of teeth;
• The machine shaft;
• Cylindrical and eccentric bearings
• protective cover;
• fasteners to connect the parts of the housing;
• chains with the necessary number of links.

When assembling a gearbox of any design, the bearings must not be replaced with bushings. Alignment between master and slave is not permissible.

An old gearbox housing of suitable size can be used as a protective housing by drilling holes in it for attachment.

• Making a homemade gearbox for a motor block starts with fixing the drive sprocket to the motor output shaft. A key or flange can be used to secure the sprocket. Depending on the design of the output shaft, even spot welding may be used.
• Machine-machine the drive shaft. The sprocket is fixed on it in the same way as on the drive shaft.
• A more reliable way is to make a shaft from two half axles, at the ends of which flanges are milled. Attach the drive sprocket between the two by bolting the entire assembly together. This option will fix the second stage sprocket more accurately and securely.
• To protect the gear mechanism from dirt and mechanical damage, it is placed in a protective housing, which also serves as a reservoir containing liquid lubricant for the moving parts.
• Drill sockets in the protective housing (crankcase) for support bearings. The drive shaft is mounted on cylindrical bearings and the drive shaft on eccentrics. by virtue of its design, changing the position in the housing within a radius of 15°, the eccentric bearing also changes the position of the drive shaft, thus adjusting the chain tension.

It is essential that the teeth of the sprocket mounted on the machine shaft be immersed in lubricating oil. When the shaft rotates, all parts of the chain reducer are uniformly lubricated.

To ensure the tightness of the crankcase, oil seals and lip seals are installed in the split and bearing seats. If standard gaskets are not suitable, a special low-strength sealant can be used.

If the calculation of the gear ratio is made correctly, the reducer, accurately assembled taking into account all the design features of your power tiller, will ensure trouble-free operation of mechanisms no worse than its industrial analogues.

Gearboxes for your power tiller

All the gearboxes of the types described above are commercially available. When selecting a new gearbox, the first thing to consider is compatibility. the unit must fit the specific model in terms of dimensions, mountings, and gear ratio. In this case, the specificity of modern power tillers is that the same model may have different engines and gearboxes.

For example, let’s compare the well-known and popular Russian single-axle tractor Neva MB2 with the traditional and new gearbox Multiagro.

• single wheel release. When rotating, one wheel can easily turn only one way;
• Shifting gears on the gearbox cover, which is inconvenient when traveling with a dolly. You have to stop, get off the cart and walk over to the tractor to change gear;
• 2 speeds forward, 1 speed backward. If you flip the transmission belt to pulleys with a different gear ratio, the number of speeds is doubled. The result is 4 speeds forward, 2 speeds backward.
• Two-wheel unlocking. Left and right locking knobs are on the steering wheel. They make it easy to turn in both directions instead of one;
• Gear shifting with cable is moved from gear housing to handlebar, which is convenient;
• more gears: 3 forward. 2 backwards. With belt flip 6 forward 2 backward.

Reliability and service life of these different models is difficult to compare yet. The new node has been on the market relatively recently, since about 2017. But it was developed and tested for a long time. In terms of functionality and convenience Multiagro has a clear advantage. It’s a Russian made, r. Saint-Petersburg, “Krasny Oktyabr” plant.

A gearbox with a gearshift on a power tiller. in fact, it gives only advantages, it is a kind of analog of a car gearbox. This is a responsible unit. With a high-quality design can have a fairly long service life. The main thing that depends on the owner to extend the service life of such nodes. a smooth inclusion of speeds, control over the amount and quality of oil.

The design of a power tiller. Key structural elements

However, the best option is a homemade gearbox. It does not need to be mated with the power plant, because the calculation is made for specific tasks, and you are not limited to a ready-made technical solution.

Changing the oil in your power tiller. a detailed algorithm for beginners

Before pouring new lubricant into the gearbox, you need to clean the mechanism from the used composition. Changing the oil is as follows:

• Park the single-axle tractor on a level, raised surface. Best of all, if there is an inspection pit in the garage. by setting the unit over it, you will be much easier to change the oil in the gearbox of the motoblock;
• There are two plugs in the mechanism. One is used to drain the used composition, and the other closes the hole where you need to pour the new product;
• First unscrew the oil fill cap. After that, place a wide container under the drain plug;
• Carefully unscrew the drain cap and wait for the used oil to drain out;
• After that, screw the drain cap all the way in with a ring spanner;
• Insert a funnel into the fill hole and add new oil;
• Then screw the cap on and unscrew it again. at the end of the cap is a 10 cm dipstick, which will help determine the amount of oil in. If there is oil at the end of the dipstick, you no longer need to refill the lubricant. For more details on changing the oil in the gearbox of a power tiller, see this video.

Under normal operating conditions, the oil in the gearbox of a power tiller should be changed no more than once per 100 hours of operation. If the machine is used around the clock, this should be done more often. at least once every 50 hours of operation. This will help prevent damage not only to the gearbox, but also to other mechanisms of the agricultural machine.

Making your own gearbox. simple about complicated

Each of the listed types of converters has its disadvantages. Therefore, in order to repair the motoblock gearbox as seldom as possible, some farmers prefer to equip their machinery with homemade converters. Makeshift construction is often better and more reliable. For the work you will need:

First the body needs to be welded. Stainless steel plates can be used for this purpose. You will also need gears and shafts for the work. They can be “borrowed” from the chain saw “Druzhba”. You will need to drill a hole inside one of the tool shafts. A second shaft must be installed on the opposite side of the gearbox, followed by the bearings and the cage. The output shaft of the device is attached to the pulley. After that the ready device should be placed in the earlier welded case and machine oil should be poured inside.

Connection of the made converter is made in the same way as that of the standard reducer. In doing so, pay attention to the position in which each pinion is located. The elements must not be twisted, and their teeth must have perfectly straight ends, with no kinks or other deformations.

At the end, it is necessary to test the inverter. It is advised not to load it immediately after creating. Start by pulling your single-axle tractor over the ground. allow the transducer elements to connect and interact. Only then can you use the equipment for its intended purpose.