Sometimes we hear allegation – what can be changed in an internal combustion engine for several tenths of years? Everything is the same!
Actually, there are a lot of changes. In this entry – about several hubs, which has changed to unfamiliarity. Why the whole entry is dedicated to this topic.
I believe, after reading this entry, you will change your perception of several as if very familiar hubs, for example – oil pump, HVA.
The structure of HVA is very simple – oil can enter inside it (under pressure, which is created by the oil pump), but can not emerge, the valve inside HVA takes care about it. Accordingly – in the moments, when the camshaft doesn’t open the valve, HVA ensures automatical “close to zero” distance between shaft and valve. For the older engine, HVA provides prevention of familiar to all “tik-tak” noise and also long life od the camshaft. Why we emphasize “for older engines”? About that – in this entry.
In this short video the performance of HVA is shown very correctly:
What consequences had “simple/older” engines of poorly working HVA (for example, in BMW M series engines)? The ticking of HVA could be heard from the engine compartment – the noise, very well known to all, especially characteristic for a cold engine. If also for the warm engine the HVA performs poorly, by the time it damaged camshaft, in most extreme cases – also the valve shaft.
In the situation, when the move of the valve (typically for “regular” engine was 8 .. 10 mm), even air gap (fault in HVA performance) of 0,5 mm didn’t have any trouble. Yes, such air gap (obviously the HVA valve leaks the oil or the oil don’t get inside the HVA) created the loud ticking, but the lift of the valve reduced just for 5 .. 7 % (from 8/10 mm to 7.5/9.5 mm).
Let’s see, what’s the situation in more modern – N series engines, which are equipped with Valvetronic.
Marked in the image:
A: distance from the point, where the Intermediate lever presses Roller cam follower to valve shaft;
B: distance from the point, where the Intermediate lever presses Roller cam follower to HVA;
7: HVA;
8: Inlet valve;
12: Roller cam follower;
13: Intermediate lever.
As you see, the distance B is around 2 times larger than A. That is not a coincidence! In such way, the BMW AG engineers had tried to reduce the impact of HVA problems to the performance of Valvetronic in idle.
Let’s remember the basic course of physics – I believe, everybody has learned, what does “lever”, “force shoulder” means. If you don’t remember – here is the basic information from Wikipedia:
https://en.wikipedia.org/wiki/Lever
The principle of the lever is used also in the image above: as the distance B is around 2 times larger than A, the impact of HVA decreases for around 2 times (comparing to movement of the Intermediate lever).
Why is it so important to decrease the impact of HVA problems on the move of the inlet valve?
As mentioned in the entry about Valvetronic, part 1, the lift of the inlet valve in idle is around 0.4 mm, but the minimal opening of them – only 0.18 mm. Comparing to the “old” engines, minimal (in idle) lift is decreased for 20 .. 50 (!!!) times! Accordingly, the impact of each technological tolerance (difference) increases for 20 .. 50 times!
If for the “old” engine the 0.5 mm air gap created ticking sound and decreased the valve opening for 5 .. 7%, then for the engine with Valvetronic the HVA play of 0.5 mm will create the difference of 0.25 mm of the valve lift. Or even more precisely – the lift of the valve will decrease for around 60% (by intended move 0.4 mm) or the valve will not open at all (if the intended lift of the valve is smaller than 0.25 mm).
We can look at the situation from another side – what would be the allowed play of HVA, so in the typical idle situation (the lift of the inlet valve is 0.4 mm) the lift of the valve would change for 5% (as for “old” engines)?
0.4*0.05*2=0.04 mm or 40 microns! So, if the HVA will “make a mistake” for only 0.04 mm, the fulfillment of the cylinder will change by 5%!
So, if the engine works in “Valvetronic” mode, requirements for HVA hub increases for at least 20 .. 30 times, comparing to a “regular” engine, which doesn’t use Valvetronic!
In case of HVA problems, it will be characteristic, that in the mode “without Valvetronic” the engine will work normally, but when the Valvetronic is switched on, mechanical efficiency of cylinders is becoming significantly different – the idle of the engine is even, it vibrates, misfires are possible.
It is self-understandable – if we hear the clatter of the valves (familiar as the “tick-tack” sound) – the problem with HVA has already overreached any reasonable range (the allowed detail play is overreached for tenths of time) and the engine, which is equipped with Valvetronic, will not be able to perform normally!
One more significant question – if we can hear the ticking of the valves – is it possible, that this defect is caused by any other component of Valvetronic, except HVA?
No! Even, if the Eccentric shaft (14), Camshaft (5), Gate block (4), Intermediate lever (13), Roller cam follower (12) will have large wear, the Spring (3) will press the Intermediate lever between eccentric shaft and camshaft, but otherwise, correctly working HVA (7) will ensure detail play of whole Valvetronic hub, close to zero.
Shape defects of the bottom part of the intermediate lever – ramp (6) (which are caused by wear), also the wear of the eccentric shaft will give distortions (the angle of the eccentric shaft/increase of the valve) in the opening curve, but it will not create the play if the whole hub (if only the HVA will perform its function).
Why was the oil pressure mentioned at the beginning of this post?
Remember – for example, the BMW M20 engine – six-cylinder power unit, installed on the retro cars, for example, E12, even to E30 of 3-rd series and E34 of 5-th series. For these engines, the perfect oil pressure oil pressure at idle was around 1.5 bar, the signal lamp started to blink by 0.8 bar.
For example, the electronically stabilized oil pressure for N series engines is 2,6 bar in idle, the max pressure in idle (when the electronic don’t reduce it) is at least 4 bar!
Of course, N52 series engines have totally different (higher) requirements for lubrication of all hubs (piston group etc.), but one of the most critical hubs, which needs oiling with stable pressure – HVA.
From everything mentioned before – forget the vintage methods (checking the play of HVA, pressing on it) in case of modern engines! The differences of several tenths of microns (even more significant – this precision has to be kept not only in a “piece” status but also in the situation when the Intermediate lever with high power presses on HVA) cannot be felt. It makes no sense to measure the air gap for switched off the engine because the problem can be present only then when the Intermediate lever presses on HVA.
How to make sure, that HVA is the cause of incorrect (different) mechanical efficiency of the cylinders?
We can perform following experiment:
- disconnect (for some time) the oil pressure sensor – in this case, the engine will switch off electronic stabilization of the oil pressure and the oil pump will develop the max pressure.
If in this mode the mechanical efficiency of cylinders is significantly different from “basic mode”- it’s a direct indication regarding problems with HVA (obviously, poorly performing HVA have increased play).
Accordingly, the HVA has to be replaced and the oiling channels have to be cleaned.
Note: the high requirements of HVA is one more reason, why timely (timely IS NOT the inadequately long interval for oil changes, defined by manufacturer) change of oil for N series engines has critical meaning.
And at last, a quite notable screenshot from the aftersales material of BMW AG: description of the structure of the N52 series engine, page 45:
Here, a shy notice regarding Valvetronic. But regarding high requirements for HVA – not a word!
Even more interesting: on page 44 of this material it’s mentioned:
The underlined text was a quite surprise for me. VANOS? But already M52TU/M54 series engine was equipped with Double WANOS! New VANOS consumes 3 times more oil?
No, it does not. BMW AG simply has bad communication between departments, the creators of the documentation have no perfect comprehension of technical nuances of the engines, manufactured by their company. There should be a notice regarding precisely maintained and even (as known, the oil pressure for N series engines is maintained between 2.6 to 5.5 bars, it means: it changes only 2 times in all working modes) oil pressure, not the oil flow rate. Most important – even in idle to ensure sufficient pressure to ensure the precise performance of HVA, decrease the changes in oil pressure in all performance modes!
In the picture: mapped oil pressure. N series engine.
A short summary of everything, described above:
- the pressure, developed by the oil pump (comparing M20 and N52/idle) has increased for at least 5 times; the precision of its maintenance – for several tenths of time;
- requirements for precision of HVA increased for several tenth times.
N series engines are only visually reminiscent to their ancestors! When diagnosing and repairing these engines, you TOTALY have to overlook the attitude for as if for certain things.
Note – if the N series engine has problems with oil pressure (and also recorded error messages regarding oil pressure or oil pressure sensor plausibility) or increased jittering of the value of the oil pump (jittering exceeds +/-15% in stable mode conditions), the problems with oil pressure has to be solved at first hand!
And in the end:
it’s possible, what exactly the problems with HVA are the reason, why both ME/MEV/MEVD and MSV/MSD series engine management systems are performing as follows:
- if the difference of mechanical efficiency of any cylinder is not possible to compensate fully, no error messages in DME error message memory are recorded, the engine management unit tries to do everything, what’s possible, leaving the applied max possible correction.
There are many reasons for short-term incorrect (or only – different) performance of HVA:
- before idle (critical mode) there was a work mode with high torque, accordingly – the oil pressure was increased; the camshaft has pressed the HVA with higher counterpower;
- when the oil (also the engine) temperature changes, also it’s viscosity changes, the fulfillment of HVA changes;
- if the engine had faults in the performance of Valvetronic or in the system of oil pressure maintenance, the work obstacles of HVA were totally different (different move of the valve and/or other oil pressure accordingly);
- finally – it’s enough for the DME engine management unit to make a mistake and, when the engine is switched off, not move the eccentric shaft to the zero position – some of the inlet valves will be kept open and appropriate HVA – with lasting load (the oil is pressed out of them with high pressure). As a result – these HVA will work differently for a long while (while they will be correctly filled with oil).
Related entries:
