Hey everyone,

The reason we typically set valve lash to .005 exhaust .004 intake is because when the engine heats up, metal expands, causing the lash to get smaller.

In my 139QMB, I have the opposite problem: the lash expands when hot, meaning .005/.004 turns into "way too loose" and causes severe ticking.

In the past, I've been able to remedy this problem by setting the cold lash to .0025 and .002 respectively. Judging by the sound when hot, there'd still be slight ticking, but nothing crazy, meaning I estimate it expands to .004/.005 or so

A couple of days ago, I took my bike for a spin, and after warming up the valves were EXTREMELY noisy. Super ticky, as if their lash was way, way too large. I assumed the lash probably expanded by itself, but when I took the cover off (engine cold), the lash was where I set it: .0025 and .002 (exhaust, intake).

What could be causing the lash to expand so severely when hot, and is it an urgent indication of imminent failure?