And finally – one more argument, which doesn’t talk in favor of HVA.
In the first two images: the opening of the valve (shape). In black color (A): a perfect valve opening in idle (0.4 mm), in red color (B) and (C) – two problematic cases, when in a result of defect the valve opens for 0.3 mm (it means, for 0.1 mm less, than necessary).
Scenario, depicted in the image above, will happen, for example, in case of large wear of the eccentric shaft. Eccentric shaft works as a multiplier for crankshaft – that’s why the valve opening shape (B) stays unchanged – it’s defined by the crankshaft, the amplitude of valve opening changes.
A similar situation will be also, for example, in case of wear of the bottom part of the Intermediate lever (Ramp – part, which gets in touch with Roller cam follower). In this time – the larger the valve opening, the more powerfully it’s spring presses, the more wear in exact point of the Intermediate lever. Of course, I simplified the situation – we don’t take into account the mechanical inertia of the valve and its spring. But tendencies are clear.
The situation is totally different if HVA has a play (image in the middle). Then the valve opens, and, as can be seen (C) – not only the max opening reduces, but also the moment of valve opening is late and total closing happens quicker!
In the third image shapes, B and C are compared.
I think, that only takes a brief glance at the images, it’s clear, that in the second case (HVA defect) the problems with cylinder fulfillment will be larger! So – by the same difference of valve move, in the second case the fulfillment of the cylinder will be much worse! This nuance, even more, increases already a high requirement for HVA and is one more obstacle, which says to me – HVA is the main cause in case of Valvetronic problems!