How it works: BMW Valvetronic

"Do not buy this engine, he has Valvetronic!" Or on the contrary "it's good because he has Valvetronic," they write BMW experts on their forums. But what is it, what it is for, and is it to be feared?

For decades in the automotive industry, the engine was supplied with fuel and air in a simple way: in the carburettor there was a rotary damper, or throttle, which either closed or opened the flow of the mixture to the cylinders. The mix sucked in the vacuum created in the suction manifold. Everything worked relatively well, with the reservation that the amount of sucked mixture was a bit random and sometimes the engine was flooding, and sometimes choked due to lack of fuel. Everything was in the hands of a capable carburetor.

In 2001, BMW introduced a revolutionary timing and air intake control system for the engine. Valvetronic had its debut in the N42 3-series E46 4-cylinder engine. Work on this solution has been carried out since the 1990s, testing various concepts. Finally, the following "architecture" was decided:

In the 16-valve head between the two camshafts, a third, central shaft is mounted, which is not driven by the timing gear, but by a stepper motor. This roller connects to pushers, which press on the valve levers responsible for opening the valve. It can thus control the lift of the valves in a smooth manner, opening and closing them in the range from 0.25 to 10 mm. The camshafts do not press directly on the valves, but on the "intermediate pusher" whose position is regulated by the Valvetronic system. It can be set even in such a position that the camshaft will not open the valves at all. 0.25 mm is no opening.

This eliminates the need for a traditional damper.
Of course Valvetronic works only for the suction valve row. Add the varistor valve VANOS (for both shafts) to this and we have an extremely advanced timing control system with a small correlation between the rotation of the shaft and the opening time and lift of valves. In addition, there is a variable length DISA suction manifold system - it is a shutter mounted in the collector, which can shorten or extend the intake system.

This video is great explained. It's Spanish, but you can do it:

BMW, as Valvetronica started to use, it soon "spilled" on the entire range. However, petrol engines without Valvetronic were also installed, eg N45 from the series 1 - weakened, simpler and cheaper. Interestingly, the N42 has a traditional throttle, whose role is to close the air supply at start-up to enrich the cold mix and react if the Valvetronic stepper motor goes crazy and opens the valves to the end.

Advantages and disadvantages of Valvetronica
On the plus side, first of all, better air dosing results in higher engine efficiency and a more responsive gas response. The efficiency increases by approx. 10% compared to the engine with the traditional throttle. It's quite a big increase, but it should not be confused with the power increase, because power is achieved at the highest speed, and then Valvetronic does not give anything anymore. His task is to make the power appear faster and smoother when you press the gas.

And the disadvantages? Certainly one of them is the increased mass of the system. An additional electric motor is an additional complication. The lack of vacuum in the intake manifold makes it necessary to add a vacuum pump to control the brakes. Well, LPG assembly is more difficult. I learned from the gas-fryer the following: under normal conditions of the gas injection map, the computer itself engulfs itself, but uses a vacuum sensor for this purpose. When the vacuum is not or is minimal, the LPG computer is fooling and making a very poor injection map, i.e., it is not enough gas. Jerking with this is only one problem, the other is the increasing temperature of combustion. The poorer the mixture in the gasoline engine, the hotter it burns. And this will cause the valve seats to burn out and other problems. Therefore, you can not just set up LPG, activate "self-calibration" and say PLEASANT READY to Valvetronica, because the customer can return with ... dissatisfied face.

Is Valvetronic spoiling?
And what does not break? In time everything will fall apart. For example, an activator motor. It happens that it simply blurs / burns and stops moving the mechanism of the levers. It stops in the position of the maximum lift of valves, and the already mentioned throttle takes over the function of controlling the air supply (or not - one mechanic claims that yes and another does not. Someone will help in the comment?). It's not everything. With time, BMW and Valvetronik start to tug and clatter in a certain range of revolutions. There are a lot of theories on this subject, because the N46 engines and their successors belong to complicated constructions. One of my friends who struggled with this problem claims that it helped replace the Valvetronic middle levers, which eventually wear out and cause the change in the valve stroke to be completely random. Only that the levers are not a substitute, and the stupid stepper motor costs PLN 1200-1500 in the ASO depending on the version (I checked only for the models that were not produced - the latest prices are probably different). Again another friend, a mechanic, claims that he was blowing the Valvetronic engine from the compressor and they were starting to work better.

So I started to read Elektroda forum and forums about BMW Valvetronic vulnerabilities in N46 and the next and, of course, I quickly accused myself of it, because everyone there quarrels with everyone and challenges the ignorant people. Most often, however, the statements were made that it is not the intermediate levers that wear, but the cams on the shaft that controls the levers and it is enough to replace this shaft. And the type that BMW is repairing said: everything is evenly used. One will first fall down the motor (activator), the other roller, and the third lever, and there is no hard rule for it. Not to mention that many people mistake the symptom of used Valvetronica with a stretched timing chain, which in N46 is the norm.

Is it necessary to advise against Valvetronic engines?
I do not think, but it is worth remembering that the E46s are already quite worn out and often they ran on oils of terrible quality or someone simply did not mention them, and this causes general degradation of the engine. There are two problems: the first is that in the case of Valvetronica's failure it is difficult to replace spare parts. You can also order them in the Dealership and put out a lightweight hand of 3-4 thousand. PLN per repair kit. The second problem is that in Warsaw or Silesia you will find a mechanic who saw Valvetronic's eyes and did not run away, but if you live in a small town and rarely go to a big city, the local mechanic can not handle it. Tips from forums are very valuable, but useless, because they end up on replacements of random parts.

Currently, all BMW engines have Valvetronic and turbocharging, making the complication even greater.

Maybe just buy yourself a diesel.