Art Webb wrote on 05/10/16 at 07:15:45:Actually a simple change to a pawless, spring-loaded tensioner could be a good solution
note that automotive serpentine belt tensioners use simple spring tension
The belts with spring tension are all driving things like water pumps, power steering pumps, air conditioners....things that don't kick back. Every cam chain or cam belt tensioner I have ever seen is either manually adjusted and locked in place - or is self adjusting and has something to resist instantaneous movement.....either a pawl, one way rod/ball clutch, or anoil/piston device that tensions and also restricts fast movements if the chain is loaded in the wrong direction.
The problem that I see with no pawl....is the valve spring will attempt to push the cam forward at low rpm, and it could result in some weird vibrations of the cam chain. When the valves are opening and closing the exhaust valve opens first and requires a strong force in the cam chain, then as the exhaust valve closes the valve spring will push on the rocker arm and cam lobe and push the cam chain forward causing slack in the cam chain, and then just before the exhaust valve closes the intake valve begins to open and it will require a strong force in the cam chain - then as the intake valve closes the valve spring will again try to push the cam chain forward and could result in some slack. When the chain tensioner locks the movement of the chain...the different loading conditions will not cause the chain to jump around.
I believe that there must be a reason that "all" engines have a cam chain or cam belt tensioner that restricts the movement "backwards". Some are sophisticated enough to allow excess tension to be released slowly as the engine warms up....the Porsche tensioners have springs that set the tension, and a hydraulic piston that restricts fast movements. Originally these tensioners worked fine - but on occasion the hydraulic part would wear out and the chain would rattle....so later on an improved version was developed that was pressure fed through a small supply line and the tensioner got a fresh supply of engine oil. Below is a photo of the early Porsche tensioners, and the spring is inside, and the tensioner is filled with oil, and there is piston that will allow the tensioner to move slowly in/out, and for installation you put the tensioner in a vice and compress the shaft slowly - then install it before the piston extends.