Tuesday, July 3, 2007

Relieving the Flathead

The second half of "port and relieve" is, of course, "relieve." It refers to the process of removing material between the edge of the valve and the cylinder bore. This is done to facilitate airflow, the thinking being that removing material in this area will give a better path for the fuel air mixture to travel as it exits the valve and makes it's way down into the cylinder.

The "relieving" had also been done on Joe's cylinders well before I got to them. As with the stock size intake valve and grossly oversize exhaust valve, the relieving had been done favoring the exhaust. In other words, the relief had been made deeper between the exhaust valve and the bore than between the intake valve and the bore. There was not a lot that I could do about this, other than smoothing out the job that was already done and making the reliefs the same from cylinder to cylinder.

I was alarmed at one point that the top ring would be too close to the bottom of the exhaust relief, exposing it to too much heat. As it worked out, by the time I had fabricated a thin "stroker" plate to go under the cylinder base to adjust the squish, the top ring was a safe distance below the relief (barely).

Now...., the way I would have liked to have approached the matter of relieving is a little different. What I would have liked to have done is treated the area between the valves and the cylinder bore like a port. Consider the floor of the "port" to be the area between the valve and the cylinder bore, which would make the roof of the port to be combustion chamber in the head. My thought is that the floor would respond better to having each "end" radiused rather than the entire floor lowered. If the actual size of this passage between the valve and cylinder bore needed to be enlarged, it may be better to remove the material from the roof.

Alas, with the relief work that was already in place on these cylinders, there was little to be done in the way of research and development.

Another area that was an obvious problem area was in the valve pockets in the heads. In fact, during initial mock up, not all of the valves would even open completely with the heads in place. Opening up the heads to match the head gasket solved the clearance problem, as well as unshrouding the valves for better airflow. Whether this interference was entirely due to the oversize valves or not is questionable. Joe had purchased new reproduction aluminum heads for his motor. Many of the head bolt holes in these heads had to be modified in order to allow them to align with the gasket and the holes in the cylinders. (Having to modify new aftermarket parts to make them fit is pretty much the standard of the industry, so please keep that in mind next time you think your local Harley mechanic charges you too much or is too slow) If the manufacturer could not even get the head bolt holes in the right place, what are the chances the chambers in the heads were put in the right place? And yes, there are apparently several different manufacturers of these heads, so don't condemn all of them because of my bad experience. I just received another set of aluminum side valve heads from a different manufacturer for another customer and the head bolt holes all lined up perfectly.

One last note, the intake manifold also needed a bit of work. I already knew that a deep V in the manifold hurts flow from testing I had done on Shovel and Evo manifolds. Since this manifold had to be made slightly wider to make up for the stroker plates, and I also wanted to convert to a "rubber band" style seal in place of the "plumber style", it only made sense to fill in the V while I was welding. With the V filled in from the outside, I was able to open it up on the inside without grinding through. I fabricated a couple of sleeves to widen the manifold as well as increase the O.D. to the came size as the intake spigots.

More than a few trips to the flow bench were involved to verify and provide future reference.

1 comment:

Jack Hester said...

Have you considered a set of the Peek seals that Tom Cotten makes, for the 'plumber' manifolds? Makes for a great seal that is better than rubber. It has memory, so it returns to it's original size and reseals to any new surface. JMO.