I am looking for a cutting tool that can be used to increase the depth of the valve relief 'eyebrow' in Merc 496 cast aluminum pistons while the pistons remain in the engine. The tool is installed in the engine valve guide in the place of the valve and is rotated by hand like a thread tap or by electric drill with the head bolted to the block and the piston at top dead center.
I am aware of the Isky Cam tool for this which I have used but it gets dull after about two hyper-eutectic cast aluminum pistons because of the high silica content and then due to its strange cutter design it is totally impossible to sharpen.
I am aware that Manley used to have such a valve relief cutting tool manufactured from an actual valve and hardened but it is no longer available from Manley. I have never used this tool but I am interested if anyone knows where there might still be available a Manley cutter with 3/8 stem for a 496 2.195" to 2.250" diameter valve head if it ever was available in that size.
Any other source for such a tool is solicited.
Any other approach to accomplish increasing the piston valve relief without removing the pistons from the engine nor the engine from the boat is also solicited (excluding doing free hand with air grinder or Dremmel tool).