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WATER PUMP TRANSMISSION BELTS: HOW MUCH DO ASSEMBLY ERRORS AFFECT THE PERFORMANCE OF THE COOLING SYSTEM AND THE KART?

Jacopo Colombo

12 November 2023 • 15 min. read

In liquid-cooled kart engines without an "on-board" water pump (i.e. not "incorporated" as part of the engine), the motion transmission system between the axle and the water pump plays a fundamental role in maintaining the optimal operating temperature for the operation of the engine (to learn more, read "Technique | Cylinder cooling" and "Technique | The radiator"). Therefore, it is of primary importance that all components of the transmission (pulley, water pump and drive belts) are mounted correctly. What happens when, on the other hand, due to inexperience, distraction or following some "paddock legend", the transmission system of the water pump is installed incorrectly? Thanks to the collaboration of New-Line Racing, we tested and measured with a special test bench the impact that the four most common installation errors have in terms of inefficiency of the cooling system or engine power absorption. And we found that every once in a while, the numbers... Lie. Or perhaps it's better to say that they are not complete!

test in points

Check the differences, in terms of water flow rate (from the radiator to the engine cylinder) and power consumption, generated by errors in the assembly of the water pump transmission.

With the support of New-Line Racing, we carried out five different bench tests:

Belts mounted in ideal conditions (correct tightening and alignment)
Belts with insufficient tightening
Belts with excessive tightening
Water pump pulley and axle pulley not properly aligned with each other
Belts mounted without a pulley on the axle, but with the correct tightening

New-Line Racing headquarters in Fiorano Modenese (Modena) - Italy

In order to have perfectly comparable situations, we did not carry out a real test on the track. We carried out bench tests instead, where the weather conditions were uniform and did not affect the results of the tests.

IN THEORY

EFFICIENCY RATIO

In order to better assess the differences between the installation of the transmission in ideal conditions and the wrong conditions, we developed an "efficiency ratio": this is the ratio between the power absorbed by the transmission during the test, expressed in hp, and the flow rate of water moved by the system, expressed in litres/minute. According to this report, the mounting system with the lowest efficiency ratio should be considered ideal. Although, as we will see in the conclusions of this test, it will not be the only parameter to consider when evaluating which is the best solution among those tested.

TIGHTENING DRIVE BELTS

There are different types of belts. We took into account the O-Ring type in this test. A key role in the proper functioning of a cooling system is also played by the tightening of the drive belt. The ideal assembly, as Marco Malverti (owner of New-Line Racing) says, can be tested by means of a very simple check: at the point halfway between the two pulleys, the belts, if pressed or lifted by pressure, with fingers, must have an oscillation of about ±1 cm with respect to the resting position. Theoretically, excessive belt tightening should generate undesirable friction with a consequent increase in flow rate, with a loss of engine power. Conversely, insufficient tightening can lead to slippage of the belts on the pulleys, which results in a poor flow of water inside the cooling system, with negative consequences on the cooling of the engine.

ALIGNING THE PULLEYS

The correct operation of the pump also depends on the alignment of its pulley with the one mounted on the axle. It may happen, however, that due to lack of experience or distraction, these two elements are not perfectly aligned on the same axis. It is easy to imagine how this can negatively affect the cooling system. But we verified it on the ground.

PULLEY ON THE AXLE

One of the elements that characterises the transmission of the water pump is certainly the pulley mounted on the axle (we have analysed some models in this "Must Have | 5 pulleys on the axle for the transmission of a kart's water pump". It is an element (made of aluminium, in the case of New-Line Racing products) that ensures the correct grip to the transmission belt, but which is not always used by everyone. In fact, the pulley is often considered an additional weight that slows down the rotation of the axle, potentially decreasing the acceleration of the kart as well. This is why several kart drivers think that not mounting the pulley, leaving the O-Rings in direct contact with the axle, may be the most advantageous choice. Certainly, the overall weight of the rotating masses at the rear axle is reduced by a few grams, but are we sure there are no other negative and crucial aspects (due to the sliding of the belt without a pulley), such as water flow rate?

BELTS FITTED IN IDEAL CONDITIONS

Efficiency ratio: 1,07

Description of the condition

In order to obtain a series of data useful for making a systematic comparison between the different situations to be analysed, the first test carried out concerned the working condition of an ideally mounted transmission. In this case, there was a correct alignment between the pulley on the axle and that of the pump. The pump was also mounted at the right angle and this allowed the drive belt to be tightened correctly to give optimal grip levels.

Checking that the drive belts are properly tightened

We used a "classic" water pump by New-Line Racing with O-Ring transmission for all the tests. All of the components were new. We made sure that external agents (such as dirt or excessive wear and tear) did not affect data collection.

Although O-Rings are basically gaskets, over time, favoured by their wide availability and low cost, they have become the most widely used transmission belts in amateur karting. However, compared to other solutions they wear out more quickly, even without excessive use (even just leaving them exposed to the sun for a period of time that is not necessarily too long, causes cracks to be created on the surface). In the photos you can see how the worn O-Rings have cracks, visible in particular when tightened. These cracks, with the stresses of the raceway, can lead to the rupture of the OR, disrupting the transmission and pumping of water from the radiator to the cylinder. This is why, if you use O-Rings, it is vitally important to prepare periodic analyses on their condition.

The test

The test was carried out in the same way as all the tests carried out, only varying the assembly conditions of the transmission of the cooling system. From the test bench made by New-Line Racing, we brought the electric engine (1.5 HP of power) to the maximum speed achievable (with the same power, the difference in speed between one test and another is given by the absorption of the pump while it works moving the water, therefore, the higher the flow rate, generally the lower the maximum speed reached by the engine), holding it for about a minute. The data collected concerned the maximum speed reached by the axle, the power used by the engine to reach that speed and the flow rate of water (from the radiator to the cylinder). Once all the measurements had been carried out, using a specific mathematical formula, we calculated the power absorbed in CV and, subsequently, the efficiency ratio of the system. The data obtained, in ideal assembly conditions, is shown below.

BELTS FITTED IN IDEAL CONDITIONS
Flow rate	46,3 l/min
Power from the engine	0,50 CV
Efficiency ratio	1,07

The test with belts mounted in ideal conditions (correct tightening)

The panel with which we control the electric engine. The screen shows the power expressed by the engine (in Amperes), which is required to reach the maximum rotation speed of the axle.

The flow meter that indicates the water flow rate during the test for the correct installation of the cooling system’s transmission.

The mathematical calculations through which we obtained the power absorbed by the transmission system of the water pump. First, you need to calculate the watts generated by the system. To do this, multiply the voltage (which corresponds to the current that allows the system to operate and which has a value of 220 V) by the maximum power generated by the electric engine during the test, in Amperes. Once the result is obtained, the watts are converted into kilowatts, and then a second conversion is made from kW to hp, taking into account that 1 kW = 1.36 hp.

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WATER PUMP TRANSMISSION BELTS: HOW MUCH DO ASSEMBLY ERRORS AFFECT THE PERFORMANCE OF THE COOLING SYSTEM AND THE KART?