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DO NOT MISTAKE!

Counting the Teeth

A little carelessness when buying a timing belt can be costly.

Anton Utkin

Today in stores there is an abundance of belts - you can pick up for any car. But first, we’ll tell you what they are in general. V-belts and multi-ribbed belts (which we will talk about next time) are used only to drive the pumps of the cooling system and mounted units (generator, power steering, etc.). The gas distribution mechanism (timing) is driven by a toothed or, as it is also called, synchronous belt that does not slip on the pulleys.

Belts of modern foreign cars are exceptionally reliable - it only makes sense to carry a new one with a set of valves or, say, a spare connecting rod … Our traditional preference for a chain drive (and a gear drive is even better!) Was brought up by VAZ. It was the owners of the Lada that surprised the world with resourcefulness: “Cut the belt along and move the sections with the cut teeth apart” … And the plant itself, not trusting the belt too much, provided recesses for the valves in the pistons of most of the currently produced “belt” motors and prescribes checking its tension already every 10 thousand km.

Having bought a foreign car, even an old one, you can relax - the proprietary timing belt serves 100 thousand km, without requiring intermediate inspections and, all the more, suspenders. And the point here is not so much in the high quality of himself (for example, the Balakovo ones are also quite tolerable), but the motor as a whole. The pulleys rotate in the same plane, the profile of the depressions of their crowns perfectly matches the belt - peak pressure concentrations are not created in individual tooth sections - and the tension mechanism eliminates the constriction of the belt. However, safety recesses in the pistons on most engines are not provided, and therefore a catastrophic “meeting” is inevitable during a break … A caring or simply cautious owner of a foreign car changes the belt ahead of time precisely for this reason.

The largest manufacturer of drive belts in the world is the American company Gates, and its timing belts are presented under the Power Grip brand. The second largest is the Italian “Dayco”, part of its production goes under the famous brand Pirelli. The third place at the German Continental concern - its belts carry the Contitech brand. The rest, small firms in our market do not sell belts, but their products (as, indeed, some of the belts made by the Big Three) are sold under the well-known brands of packaging companies, for example Bosch, TRW, etc.

For automotive timing belts, as well as for chains, four tooth steps (links) are provided. Traditional - 3/8 inch (9.525 mm). In recent years, metric is increasingly being used - 8 mm. The remaining two - 8.22 mm and 5 mm - are rare. There are also 36 belt widths (from 8.6 to 36 mm), the exact correspondence of which is no less important than the pitch and number of teeth. A wider belt will not fit into the brook of the tension roller, and a narrower one will walk along the pulleys, causing bending and accelerated wear of the teeth, and even completely break off from the emergency load. And the last thing that determines the suitability of the belt for this machine is the tooth profile. It should correspond to the depressions on the rims of the pulleys as calculated by the engine designers.

Nowadays, about a dozen varieties of profiles are used: four of them, developed in different years, are shown in the figures. Previously mastered, as a rule, are trapezoidal, and the tops of the teeth do not reach the bottom of the pulley cavities. Belts for motors of the latest models - with high-profile semicircular teeth: they abut against the bottom of the troughs, which makes it possible to distribute the load over a larger contact area.

The international designation of a gear belt includes all the mentioned data. For example: 58127x3 / 4 HSN. In the first two digits (58) a series of teeth is encrypted, that is, their profile and pitch - in this case, semicircular, without a groove, 3.6 mm high with 3/8 "increments. The next three digits (127) - the number of teeth (for belts 40 series it is conditional). After the multiplication sign - the width of the belt in millimeters or inches (here 3/4 "or 19 mm). The HSN abbreviation at the end of the marking stands for the highly durable belt material - “Highly Saturated Nitrile”, and if it is not there, then the belt is made of traditional neoprene rubber.

Data synchronous belts for most common cars in Russia are shown in the table. Belts for obsolete cars of the 70s-80s, forced modifications of engines, rare and expensive models were not included in the list. Also not included are short (45–70 teeth), not intended for camshaft drive and used in addition to the main belt to rotate balancing shafts and diesel fuel pumps on some motors. Do not be surprised if you do not find in the first column of the table American cars, Mercedes, many modern models of Nissan, Toyota and other companies - their designers preferred the chain. Unlike a belt (or, say, a “Zhiguli” chain), it will almost never have to be replaced. In addition, they put the chain if compactness is very important: after all, a belt drive, whatever one may say, lengthens the motor by twenty millimeters.

Cases of interchangeability of timing belts are quite rare. The engineers calculated which belt they would order from Gates or Conti. Another thing is our auto industry, where prototypes of units, and the machines themselves, are always a bizarre mixture of imported components. It is then that parts from Balakovo, Stavrovsky and other allies will go onto the conveyor, and first Deiko, Solex, Bosch, Saks, etc. will be attached. So, they picked up a belt from an old FIAT to VAZ 2105, to " Tavria "- from Toyota, and to the 16-valve VAZ 2112 engine - from Citroen. The remaining matches in the table are explained even more simply - the same motors (or similar licensed ones) can be used by different automobile companies. Say, belts 41121x18 and 90152x25 HSN are powered by Audi and Volkswagen engines, 76092x29 HSN and 76163x1 HSN engines are Mitsubishi and Hyundai, and 58127x3 / 4 HSN are Volvo and Renault.

PROFILES OF SYNCHRONOUS BELTS

BY ISO STANDARD

1. Trapezoidal series 41 (form C).

2. Semicircular series 58 (Form R).