«Do not buy this engine, it has Valvetronic!» Conversely, «it's good because it has Valvetronic,» write BMW experts on their forums. But what is it, why is it needed, and should you be afraid of it?
For decades in the automotive industry, the engine was supplied with fuel and air in a simple way: a rotating damper or throttle was in the carburetor, which either closed or opened the flow of the mixture into the cylinders.
The mixture is sucked in a vacuum created in the intake manifold. Everything worked relatively well, with the caveat that the amount of mixture sucked in was random, and sometimes the engine flooded, and sometimes it suffocated due to lack of fuel. Everything was solved by the carburetor.
What is Valvetronic
In 2001, BMW introduced a revolutionary valve train system for the engine.
Valvetronic debuted in the 4-cylinder N46 engine of the E46 3 Series. Work on this solution began in the 1990s, testing various concepts. Finally, the following «architecture» was adopted:
In the cylinder head with 16 valves, a third central shaft is installed between two camshafts, which is not driven by a gear wheel, but by a stepper motor. This roller is connected to pushrods that press on valve levers responsible for opening the valve.
Therefore, it can smoothly control the lift of the valves, opening and closing them in the range from 0.25 to 10 mm. The camshafts do not press directly on the valves but on an «intermediate pushrod,» the position of which is regulated by the Valvetronic system. It can even be set in a position where the camshaft does not open the valves at all. There is no 0.25 mm hole.
The traditional damper is no longer needed.
Of course, Valvetronic only works for a series of intake valves. Add to this the VANOS valve (for both camshafts), and we get an extremely advanced timing control system with little correlation between shaft rotation and valve opening and lift.
Furthermore, there is the DISA variable length intake manifold system — a throttle installed in the manifold that can shorten or lengthen the intake system. This is well explained in the video. This is Spanish, but you can do it too: BMW, as it began to use Valvetronic, soon «spread» throughout its range.
However, there were also gasoline engines installed without Valvetronic, for example, the N45 from the 1 Series — weakened, simpler, and cheaper. Interestingly, the N42 has a traditional throttle valve, the role of which is to close the air supply at startup to enrich the cold mixture and react if the Valvetronic stepper motor goes crazy and fully opens the valves.
Advantages
On the positive side, Valvetronic: first and foremost, better air dosing leads to increased engine efficiency and faster throttle response; efficiency increases by about 10% compared to an engine with a traditional throttle valve.
This is a significant increase, but it should not be confused with an increase in power because power is achieved at maximum speed, and then Valvetronic does not provide anything else. Its task is to make the power feel faster and smoother when pressing on the gas.
Disadvantages of BMW's Valvetronic
Undoubtedly, one of them is the increase in system weight. An additional electric motor complicates matters. The absence of vacuum in the intake manifold necessitates the addition of a vacuum pump to control the brakes. Well, assembling liquefied petroleum gas is more complicated.
From an operator working on gas, I learned the following: under normal gas filling conditions, the computer absorbs itself, but for this, it uses a vacuum sensor. When vacuum is absent or minimal, the LPG computer goes crazy and makes a very poor injection map, meaning there is not enough gas.
The jerk with this is just one problem; another is the increase in combustion temperature. The leaner the mixture in a gasoline engine, the hotter it burns. And this will lead to the burning of valve seats and other problems. So you can't just tune the LPG, activate «self-calibration,» and say «PLEASE, READY» to Valvetronic because the customer may come back with... a dissatisfied face.
Does Valvetronic Fail?
What doesn't break? Everything will deteriorate over time. For example, the engine actuator. It happens that it just wears out / burns and stops moving the lever mechanism. It stops in the position of maximum valve lift, and the aforementioned throttle takes over the function of controlling the air supply (or not — one mechanic claims yes, another no.
That's not all. Over time, BMW and Valvetronic start to pull and rattle within a certain range of revolutions. There are many theories on this issue because the N46 engines and their successors are complex constructions.
One of my friends who struggled with this problem claims that replacing the intermediate Valvetronic levers, which wear out over time and lead to completely random changes in valve stroke, helped solve it. Another mechanic, however, claims that he blew out the BMW Valvetronic engine with a compressor, and they started working better.
So I started reading car forums and topics about vulnerabilities in BMW's Valvetronic in the N46 and subsequent models. Of course, I quickly blamed myself for this because everyone there argues with everyone and constantly challenges their own ignorance.
Most often, however, statements were made that it is not the intermediate levers that wear out, but the lobes on the camshaft that control the levers, and that is enough to replace this shaft. And the type that repairs BMWs said: everything wears out evenly.
One will first fall on the motor (actuator), another roller, and the third lever, and there are no strict rules for it. Not to mention that many people mistakenly attribute the symptom of a used Valvetronic to a stretched timing chain, which is normal in the N46.
Read more about BMW models on the site section.
Is Valvetronic Necessary
I don't think so, but it is worth remembering that E46s are quite worn out by now and often used oil of terrible quality or someone simply did not mention them, causing overall engine degradation. There are two problems: firstly, in case of Valvetronic failure, it is difficult to find spare parts to replace it.
The second problem is that it is unlikely that you will find a mechanic who has seen Valvetronic in the eye and not run away, but if you live in a small town and rarely go to a big city, the local mechanic definitely won't cope with it. Forum advice is very valuable but useless because it ends with the replacement of random parts.
Currently, all BMW engines have Valvetronic and turbocharging, which complicates the situation. Maybe just buy a diesel.
