Quote:
Originally Posted by Barry_R
A roller tip rocker or a rocker on an SOHC engine will not have any rotation force on the valve at all beyond the very small (10 degree?) partial movement cause by the spring winding as it compresses. There is nothing there to cause the valve to rotate. Nothing. The normal and proper wear pattern on the tip of a race valve is a nearly straight line with no indication of rotation.
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TL/DR: Eppur si muove. In fact, I don't think you can stop them from rotating unless you actively prevent it (mechanically).
Valve rotation: When a valve spring is compressed it twists. This twisting motion is imparted to the valve. I suspect inertia of the valve (spring, retainer, keeper) makes the assembly rotate. I also suspect the fleeting transition in motion from down to up plays some part in facilitating the rotation. Rotation evens out the heat on the valve and seat, helps to prevent the stem from sticking in the guide, and wipes carbon from the valve face and seat. Granted, I need to think about the physics more. Happy to hear any thoughts you all might have.
This leads us to Damage's marked valves. Why were they marked 360 degrees around the edge? I seriously doubt the valves were marked after the timing chain broke. Even though all hell does break loose after a timing chain breaks, I believe there are still clues in the aftermath. When the chain breaks, the valves stop opening and closing; therefore, they stop rotating. The 360 marks must have happened when the engine was running. There is simply no other conclusion that can be drawn. There are valve marks on the pistons. The pistons do not have valve relief 360 degrees around them. The valves have 360 degree marks on them. Therefore, the valves must have rotated during operation.
Was rotation cause by bent valves? I doubt it. Here's why. David Trask is among the very elite of the most elite athletes/drivers in the world. His skill, talent, reflexes, and experience is beyond what I can understand. I believe had the valve bent while David was driving he most certainly would have heard it/felt it/realized it and shut the engine down. I imagine during his career he very well may have gone through more engines than all of us combined. He is finely attuned to mechanical failure. F1 is not for the feint of heart. His life depended on hearing, feeling, seeing very subtle changes in his equipment and taking immediate, decisive action before tragedy occurred. No F1 title is worth his life. He knows when he has to shut down and he would have done it.
So, what is the most logical explanation? Quite possibly the valve to piston clearance was very, very tight...perhaps slightly too tight. Could a tapping have have led to instability in valve train, thus weakening the chain? I don't think we can rule that out.
Please take my comments as someone who is doing an autopsy from 7,000 miles away across the internet. I fully welcome differing points of view and thoughts. Indeed, I may be wrong in my thinking and am happy to be corrected. I only offer a theory, which certainly may be proven in error by any facts someone else can bring to this discussion.
Below are high speed videos of valves rotating.
[ame=http://www.dailymotion.com/video/xyejoc_engine-valve-rotation-valve-guides_auto]Engine Valve Rotation & Valve Guides - Video Dailymotion[/ame]
[ame]https://www.youtube.com/watch?v=019Jyn9oB5k[/ame]
[ame]https://www.youtube.com/watch?v=WtqDHJDN79w[/ame]