It doesn't take much curve to get decent chain control though.
BTW - On that Nissan, the tensioner is on the slack side (passenger side) The elliptical guide on that side has a bottom pivot, and an oil-fed piston presses the top into the chain.
- Bill
Completely agree on that comment, Bill. It doesn't take much. When you watch a chain at speed you can see it coming off the gear and wanting to continue in an outward motion, even when it's being "pulled". That causes irregular movement and plays havoc with the timing and really stresses the chain at the same time. edit: You can easily see this with a timing light and a worn out timing chain as the timing jumps around on the damper. And that's on a VERY short chain compared to the SOHCs chain!
That Nissan using a pivoted guide as a tensioner is a pretty good idea. It would be much easier to fabricate than an actual tensioner arm. I do believe that controlling that chain would have some pretty big benefits in an SOHC. I'm not convinced that the old thought of the chain "stretching" at speed was the cause of the cams timing being moved around, but rather the chains centrifugal force and generating uncontrolled slack in areas was probably more likely the cause. It would be interesting to see high speed video of that chain in action.
And Jay, I had time to look for that video of the valve head and could not find it again. It was not on YouTube, but a high end engine sight that documented reasons for advancement in valvetrains. Coil springs are nearly impossible to control without a damping device, and that technology just hasn't been seen yet.
