In this entry we will look at possible defects of Valvetronic components due to wear, and what effects these defects have on the valve lift.
We assume, that BMW AG has manufactured perfect details, and they are damaged exactly due to wear.
First basic thing – components, which rely on all cylinders (for example, detail play of the bearing of the eccentric or camshaft), will no give problems to only one or two cylinders. Accordingly – if only separate cylinders have any problems, we have to inspect components, which are separate for each cylinder.
1. Camshaft (5). The surface of the camshaft slips over Intermediate lever in each intake cycle, it means, wears of friction – potentially high. At the same time – the camshaft in this construction is “before” the Intermediate lever, which means – small wear of the camshaft will not give any problems. If, for example, transformation coefficient of the Intermediate lever is 1/25 (0.04 = idle mode), 0.1 mm wear of the camshaft will give a decrease of 0.1 * 0.04 = 4 microns for the move of valve lift. Such a fault will not give problems. Conclusion – if there are no significant (visible) defects of the camshaft – it cannot be the cause of unstable idle.
2. Eccentric shaft (14). The impact of the eccentric shaft to the valve lift is very significant – defects of its surface will give a decrease of the valve lift, which can be compared with this defect. It is characteristic, that relationship 1:1 of wear/problem was typical of the 1st generation of Valvetronic. 2nd generation (thanks to Gate block) has decreased impact of the defects of the eccentric valve in the range of small valve opening is decreased for several times: for the 2nd generation of Valvetronic, we can assume that the shaft defect of 0.1 mm will give a decrease of valve move for 0.02 .. 0.03 mm. But Intermediate lever slips over the eccentric valve only when the performance mode (requested torque) of the engine changes (the lift of the valve has to be changed). These changes are happening rarer then valve opening cycles. Rotating moves of the Intermediate lever, which are happening in the touching point of these details are small, accordingly – we can not worry – other details will wear more faster!
3. Intermediate lever (13) – it’s connection point with the eccentric shaft: will wear insignificant, because (main) move with the eccentric shaft is, when the engine performance mode changes, moreover, the wear of this surface will be compensated by HVA. Connection surface with the camshaft will wear faster (because the surfaces are slipping one against other in each cycle of the valve opening), but the impact of the wear reduces according to the Intermediate lever transformation coefficient – the problem will not increase within the range of small valve opening. The bottom part of the Intermediate lever (ramp), more precisely – its shape, not absolute wear (part, which touches with Roller cam follower) gives the more critical impact to the valve opening. Even more – the match of this shape is a match between cylinders. Moreover, this surface wears quickly – Intermediate lever slips over Roller cam follower in each cycle of valve opening and receives a blow if HVA doesn’t perform correctly. And again – the absolute wear of this shape will be compensated by HVA.
Note: premature damage of eccentric valve (especially characteristic Generation 1 of Valvetronic) and Intermediate lever (both in the touching point with the eccentric shaft and Roller cam follower); Gate block (Generation 2) is caused by a defect of HVA – detail play.
4. Valve (8) shaft. Valve shaft will not be the one to blame unless HVA was not catastrophically damaged and Roller cam follower has not damaged it (valve shaft) so bad, that even replaced and correctly working HVA will not be able to ensure normal performance of the hubs.
5. HVA (7). As already mentioned before, HVA is critically important for the normal performance of Valvetronic. The impact of this hub is very significant to the valve lift – it decreases the valve opening for 1/2 of HVA detail play, it means, it is very significant exactly for small valve lift mode (idle) – even tiny: 0.1 mm discrepancy in HVA performance will create valve decrease of 0.05 mm (decrease it for 15% in idle, in turn, in full load mode will be only 0.7% – will be no problem).
6. Gate block (4) will not be the real cause. In this point, the Intermediate lever performs a change of position only, if the position of the eccentric shaft changes – it happens relatively rare. In turn, rotation move at this point is in very small range. And additionally to all – correctly working HVA will compensate wear of this hub.
7. The critical surface of Roller cam follower (12) – part, on which Intermediate lever slips. Also here (exactly as for Intermediate lever) the change of shape is very critical (because in case of correct shape the difference of sizes od Intermediate lever/roller cam follower will be compensated by HVA). Have to remark, that the impact of the change of shape to the valve lift is significantly smaller than for Intermediate lever.
Brief summary
Most critical (from the point of view of wear) positions, in sequence from less critical to most critical:
- shape of Roller cam follower surface, where it touches with an Intermediate lever; eccentric shaft;
- shape of Intermediate lever surface, which touches with Roller cam follower (ramp) – not without a reason exactly this element is sold under several different codes, according to measured parameters;
- correct performance of HVA – increase of the problem is typical exactly for low valve shift – idle mode (the impact of the problem is inversely proportional to max valve opening).
An at last – the image, which graphically displays the impact of more typical damages (exact wear, for example, 0.1 mm) impact to the valve lift.
A: camshaft and wear of the Intermediate lever in point, which gets in touch with the camshaft. The impact of the defect is unchangeable and relatively small in all range;
B: the impact of the wear of the eccentric shaft for the 2nd generation of Valvetronic;
C: impact of the HVA;
D: impact of the wear of the eccentric shaft to the 1st generation of Valvetronic.
The Intermediate lever (part, which touches Roller cam follower – ramp), is not marked in the graphic. The impact of this wear is very specific:
a) absolute wear – it’s compensated by HVA, impact = 0;
b) change of shape – the impact is 1:1 (high, analogous to the impact of the eccentric shaft of the 1st generation of the Valvetronic);
c) change of shape changes the valve opening, but even more significant it changes “shape” of the opening.
The impact of
- 1st generation Valvetronic eccentric shaft and Intermediate lever (shape of the “bottom” part – ramp) is the highest (1:1);
- HVA follows with 1:2;
- 2nd generation Valvetronic eccentric shaft decreases several times (to 1:3 .. 1:5) in range of small valve opening;
- the camshaft defect is small in all range of valve performance (around 1:20).
Here we have to remember one very important nuance: looking at the wear of shafts: Intermediate lever or other parts, we usually look for smallest (0.1 mm and less) signs of wear, in turn, HVA can cause much more serious problems without any sign of wear!
Look, how the impact of defect changes, if we loot to the problem of point of view – lasting disbalance of mechanical efficiency between cylinders:
A: camshaft and wear of the Intermediate lever in point, which gets in touch with the camshaft. The impact of the defect is unchangeable and relatively small in all range;
B: the impact of the wear of the eccentric shaft for the 2nd generation of Valvetronic;
C: impact of the HVA;
D: impact of the wear of the eccentric shaft to the 1st generation of Valvetronic.
What is the nature of the assumption?
Mechanical disbalance of cylinders (Rough run data) point to DIFFERENCES in cylinder performance.
Accordingly – look directly at differences, not absolute values.
Both eccentric shaft and Intermediate lever are passed EVEN NUMBERS of cycles. Compression force (counterpower of valves and return springs) between these details is similar; temperature and other obstacles (including – sectors of details, which are subjected to wear) – similar. Of course, the situation is not possible – detail wear on one cylinder details is maximal, but details of other cylinder are not worn at all. I suppose that the difference between cylinders reach 25 .. 30% (it means, for example, by absolute wear of 0,1 mm differences between detail wear of different cylinders is to 0.03 mm). My basic knowledge of mathematics and physics say, that 25 .. 30% could be average pessimistic prognosis (it means, the real situation will show better coincidence of wear between cylinders). Absolute wear has to be compensated by HVA – it is not interesting for us (because the disbalance of cylinder efficiency marks the differences directly between components of cylinders). Accordingly: the impact of defects of A, B, D type decreases to 25 .. 30 % from initial.
In turn, specific defects of HVA (not-airtightness of the valve, micro scratches in the walls of cylinder etc) will be individual to exact HVA! HVA “don’t wear” for all cylinders similarly as the metal details, when they are slipping for X numbers of cycles!
As we can see, HVA takes up the lead mathematically with at least double/triple!
Moreover, this dominance doesn’t take in account HVA’s “aggravating circumstances”:
a) HVA are taking a load in each cycle of the valve lift, not only then (for example), when the eccentric valve change position;
b) it’s common to evaluate HVA detail play (and checking it – pressing it), not evaluate its performance precision with a step of 0.05 mm or even less;
c) problems of the HVA performance cannot be seen, they can not be evaluated not “outside the engine”, not when the engine is working, they are impacted by external circumstances: oil pressure in its pit (it also can’t be measured) – defect can hide very well;
d) unlike the wear, the defects of HVA can be “slipping” – it means, they can change according to engine temperature, oil condition, in one moment it can increase, in other – decrease without reason.
Example No.1. 2nd generation of Valvetronic. Average wear of the eccentric shaft around 0.1 mm versus detail play of HVA of some cylinder of 0.1 mm: in case of HVA problems mechanical disbalance of cylinders would be 5 .. 8 (!!!) times higher. Or: HVA defect around 0.02 mm will create as much disbalance at the wear of eccentric shaft for around 0.1 mm.
Kexc = 0.3*0.2 (30% a predicted difference of the shape and 1/5 transmission coefficient, thanks to Gate);
Khva = 1*0.5 (completely independent, or 100% defect and 1/2 transmission coefficient, thanks to Roller cam follower).
Example No.2. 2nd generation of Valvetronic. Switching off cylinder X, Rough run displays its efficiency of 0%, which corresponds to +6.0 units. With cylinder X, switched on: Rough run displays it’s efficiency +3.0 units (50% or needed). Obviously, the inlet valves of a damaged cylinder are opening less than needed. We can make very approximate assumptions, that the opening lift of valves is decreased for 25 .. 50% (if there is a play in the hub – when the opening lift decreases, opening time also decreases). Let’s look at the most optimistic scenario (with the smallest wear). By opening 0.4 mm (idle) 25% decrease of each valve opening will be 0.1 mm.
In case of HVA defect – the play has to be 0.2 mm; a difference of the eccentric shaft between cylinders – above 0.4 .. 0.5 mm, predictable absolute wear: several mm!
The difference of the shape of the bottom part of the Intermediate lever (ramp) between cylinders has to be at least 0.1 mm, predictable average wear – at least 0.3 mm.
If we assume, that only one inlet valve (not both) is damaged, the amount of the damage has to be even more dramatical. It’s clear, that such catastrophic damages of the eccentric shaft or Intermediate lever can be identified with “unarmed eye”.
In turn, if such dramatic damages cannot be seen, it’s obvious, that the mechanical efficiency is caused by other reasons, not damage of these details.
Example No.3. Lift of one inlet valve relatively decreased for 0.1 mm, which corresponds to efficiency drop around 15% (if the move of valves is 0.4 mm in idle). Summarized in the table: required wear/the amount of defect, which provides such decrease of valve move.
(1) it’s assumed, that differences between valves are around 30% from a total wear;
n.a.: within reasonable limits – it cannot cause such a huge deviation from a norm.
Note: allegations mentioned above and calculation are, of course, simplified. I’m looking for most dominating components of each problem. I don’t doubt, that BMW AG has accurate mechanical models and a huge amount of data for simulations of wear. Most significant – in my opinion, a huge amount of Valvetronic parts are replaced without identifying the real cause of the problem: HVA.
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