my B18C was burning a lot of oil so i tore the head off, come to find out that 3 of the cylinders have a weird circumferential grove in them its not vertical, it runs about half way around the cylinder in a radial fashion. and its not toward the sides of the cylinder either, its toward the clutch end of the engine. with piston at BDC, the grove is about half a inch above the top of the piston. any idea what could have caused this? i know its hard to see, but it right below the discolored part of the cylinder wall. you can see the light reflecting off of the bottom of the grove toward the right side of the picture. as far as i can tell, its about 10 thou deep.