On my current build, Ive just discovered tjis on the head whilst getting ready for blasting. Got a new one coming, gonna probably get it properly fitted, as the seat may need cutting.
I guess they usually wear out before they crack! I remember my 94 900 going in to Baines for replacement head studs - one broke on the vertical cylinder - and even though it had only done around 14,000 miles, they checked if there was any sign of valve guide wear. The guides were eventually replaced at somewhere between 40 and 50,000 and probably need doing again soon as it does smoke a bit on the overrun now at around 75,000 on the clock.
no, excessive seat and valve wear allowing the valve travel to reach the taper of the valve head to enter the guide and create the split ?
Maybe, the history of the engine is unknown by me. Its carby heads on injection barrels and bottom end, so theres gonna be more wear up top. Bottom end is in good condition
