So this application was driven by the type of build and modifications required for an increase in performance. The component in question is an exhaust valve seat that maintained the outside diameter but allowed for an increased inside diameter. Directly out of the catalog there were no seats that matched, so I located the best one that could be modified for what I wanted.
The seats had the same 1.062" OD but had an ID that was about .085" too small. I could have installed the seats in the cylinder head and then bored them to the desired dimension, but the center is based on the center of a pilot, so they would all be different once installed and machined. And, our machine cannot bore a seat that small, the OD is only slightly larger than an inch.
So to make them all the same I decided to perform the boring before the seats were installed in the head. This process began with designing and building a fixture to hold the seats.
The fixture first was squared with a shoulder so it could be mounted in a vise on the mill and be square to the machine. After flipping the top was slotted to allow a flexible clamp. After the slotting the next step was to machine the bore that the seat would "sit". That bore was nearly the same size as the seat so it required a little tapping to get it in. Below the seat I machined a counter bore to allow the boring head a little over-travel after finishing the seat boring. The final fixture construction step was to drill two holes off center to accomodate two clamping bolts which squeeze the seats in the fixture. Now it's built so lets do some machining.
Matt W.
North Texas Speed and Machine
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