SOTP Vintage Series
Main Motorcycle: The one between my legs
Join Date: Feb 2009
Location: Upstate NY
Other Motorcycle: A few
Extra Motorcycle: Yes
I truly hope I am wrong about this as far as this causing problems in actual practice. I would want to see the factory dwg regarding that chamfer you mention. A chamfer is really just the breaking of a sharp that edge and has dimensional limits. Normally set at 45 degrees. Most chamfers are no more than 1/16 deep, although the size of the bore would determine the final depth. What you did is make a tapered hole. That's not a chamfer. And there is a tool specifically engineered to assist with the o-ring installation. That alone tells me that the chamfer was to assist in the positioning of the tool and placement of the o-ring, but not meant to work in this capacity by itself. Having been a machinist, I know that chamfers like this are rarely measured. A 45 degree cutter is placed in the toolhead and the operator comes down and kisses the edge of the bore to break the sharp edge. The result is some get kissed a little more than others, especially in production work. I would think this is the reason some did not get the chamfer. They probably did, just not very deep.
We are not talking huge numbers here. If you can slip that shaft into the cover with your fingers, then there is clearance between the shaft and the bore of the cover. Not much, but clearance nonetheless. That means that the o-ring, although significantly compressed, is still the largest diameter of that cap and hence is the pivot point for any angular movement . Everytime that rocker opens the valve, the shaft bends, an extremely small amount, but bends for sure. When it does, the cap tilts relative to the bore with the o-ring as the pivot point. The shaft also moves up and down perpendicular to the bore due to clearance. So the more surface area supporting the cap, the larger the area across which those forces are spread.
I truly not trying to rain on your parade, Ed. If this was just you and me in your garage, I'd probably never have said anything because it was too late and saying anything would not add any value at that point. But since several have liked the idea and others come to the forum for advice, I felt I should point out why I think this is a bad idea. At least this way, others can see both points of view and decide for themselves.
I base my opinion on good mechanical design practices, formal training as a machinist in my formative years and working working with very large, high tech, rotating equipment for nearly 40 years. It is not based however on any experience with Triumph engines, or specifically the 500 twin.
Again, respectfully submitted,