Valvetrain geometry...DRE/T&D/Jessel
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From: Port Tobacco, MD
Valvetrain geometry...DRE/T&D/Jessel With the latest post about the Comp/DRE rockers, I saw some negative press about the rockers and their geometry. What makes valvetrain geometry good or bad?
Phillip
Phillip
Re: Valvetrain geometry...DRE/T&D/Jessel I did have to open the pushrod hole for the T&Ds I recieved in 2000.
They also came with the wrong torque numbers for the shaft bolts (an M8 55 lbft into aluminum?!?!?!) and two rocker bolts broke, creating quite a "rattle"
chris
They also came with the wrong torque numbers for the shaft bolts (an M8 55 lbft into aluminum?!?!?!) and two rocker bolts broke, creating quite a "rattle"
chris
Re: Valvetrain geometry...DRE/T&D/Jessel Well, lets look at the rocker from the side, and think about it a bit.
Since the rocker pivots about a fulcrum, both ends will travel through an arc when the rocker rotates. If we can assume for this first section that the valve stem and the pushrod are parallel, I would think that we want the rocker to travel an arc that is symmetric about the angle perpendicular to both. In other words, if the rocker travels 30 degrees from 0 lift to peak lift, we want the rocker to start at 15 degrees tipped towards the pushrod and ends 15 degrees towards the valve. This does two things. This maximizes the net forces exerted on the valve that is placed on the pushrod. The other thing that this does is it allows the tip of the rocker ot travel the smallest path over the valve stem tip. Side loading of the valve stem by the rocker is harmful beyond a certain amount. Lastly, it minimizes the side-side travel of the pushrod. This side-side travel of the pusrod exacerbates flex and can create it's own valvetrain resonances which in turn cost power.
Secondly, I think that these issues should be minimized when the pushrod and valvestem are parralel, and whenever they are not, they create sideloading of the valve or sideloading of the rocker by the pushrod. Both of these are wasted forces, and wasted forces are bad in wear-prone environment. You could, in theory raise or lower the cup and tip over or below the fulcrum in order to compensate for pushrods and valves that are not parallel. As long as a plane perpendicular to the valvestem or pushrod passes through the fulcrum of the rocker, you are all set.
thirdly, I think the rocker needs to try and place the midpoint of the pushrod cup and valvestem tip as verticlally on the same plane as the rocker fulcrum as possible if the pushrod and valvestem are parallel. If not, the arcs of both are moved up or down away from the arc midpoint we were looking for earlier.
Thats my educated guess at ideal valvetrain geometry...
chris
Since the rocker pivots about a fulcrum, both ends will travel through an arc when the rocker rotates. If we can assume for this first section that the valve stem and the pushrod are parallel, I would think that we want the rocker to travel an arc that is symmetric about the angle perpendicular to both. In other words, if the rocker travels 30 degrees from 0 lift to peak lift, we want the rocker to start at 15 degrees tipped towards the pushrod and ends 15 degrees towards the valve. This does two things. This maximizes the net forces exerted on the valve that is placed on the pushrod. The other thing that this does is it allows the tip of the rocker ot travel the smallest path over the valve stem tip. Side loading of the valve stem by the rocker is harmful beyond a certain amount. Lastly, it minimizes the side-side travel of the pushrod. This side-side travel of the pusrod exacerbates flex and can create it's own valvetrain resonances which in turn cost power.
Secondly, I think that these issues should be minimized when the pushrod and valvestem are parralel, and whenever they are not, they create sideloading of the valve or sideloading of the rocker by the pushrod. Both of these are wasted forces, and wasted forces are bad in wear-prone environment. You could, in theory raise or lower the cup and tip over or below the fulcrum in order to compensate for pushrods and valves that are not parallel. As long as a plane perpendicular to the valvestem or pushrod passes through the fulcrum of the rocker, you are all set.
thirdly, I think the rocker needs to try and place the midpoint of the pushrod cup and valvestem tip as verticlally on the same plane as the rocker fulcrum as possible if the pushrod and valvestem are parallel. If not, the arcs of both are moved up or down away from the arc midpoint we were looking for earlier.
Thats my educated guess at ideal valvetrain geometry...
chris
