In several forums and blogs, I’ve seen a “copy/paste style” recital about the problem, which is characteristic to Valvetronic of Generation 1.
Here, the image:
With A in the image the place of the hub, where, according to the author of the version: when it wears, the move of the valve decreases and as a result – it’s mechanical efficiency decreases etc:
”One of the main problems with the first generation Valvetronic system was the contact point between the intermediate lever and eccentric shaft. This point is a sliding contact pad and was susceptible to wear if oil maintenance was neglected. This contact point is subjected to the pressure applied by the closing pressure of the valve spring pushing up on the roller follower and intermediate lever. As this contact point wears, the actual valve lift will decrease and cylinder-to-cylinder air intake quantities will vary and cause idle roughness”
Note: the false statement is marked.
Actually, HVA has to be able to correct this situation.
With the yellow line, the new (worn out) surface of the Intermediate lever is marked (let’s assume, that it has worn for 0.1 mm). Accordingly, HVA is supposed to press Roller cam follower “up” (the spring also helps for this move), it, in turn, has to press the Intermediate lever, till it reaches eccentric shaft, it means, moves for 0.1 mm. To reach this, HVA has to increase it’s “length” for around 0.3 mm (that’s why the red arrow, which covers it, is larger).
When the worn Intermediate lever has (again) reached eccentric shaft, the hub works practically “as new”.
If as a result of wear, the play in this hub appears (between eccentric shaft and Intermediate lever or Intermediate lever and Roller cam follower), the defect has to be found in HVA!
Of course, significantly changed surface of Intermediate lever in point A will change the valve opening shape (its shape will not be perfect parabola) – the position of Intermediate follower in position A will slightly change, when it will perform rotation mover, which are caused by camshaft, but the changes of valve move for sure won’t be “Intermediate lever wear for 0.1 mm, because the movement of the valve decreased for 0.1 mm”! The valve move will not decrease due to wear of Intermediate lever!
If the eccentric shaft has worn, the move of the valve will decrease – decrease will be comparable with the amount of wear of shaft. But we have to take in the account, that the wear will be “smeared” in the shaft sector (it won’t be in one position/point), and additionally, the wear will be not only for one or several cylinders – this defect usually don’t give huge permanent difference of mechanical efficiency between cylinders.
Note: exactly the defect of HVA (as a result – detail play of all hub) will be the cause for premature damages of the upper part of the Intermediate lever and eccentric shaft.
