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I just read two older posts about a fresh rebuild followed by exhaust valve failure. In one case (2012), 3 of the 4 valves fell and stopped the engine from starting. It sounded like it happened before any major damage occurred. The other case (2018) was similar to my experience, where he got 10-15 minutes of run time before a valve dropped and punched a hole in the piston. In every case, the timing was double checked and believed to be correct. At least 2, if not all 3 cases, the valves themselves were not touched. It was always exhaust valves, and often 2 or more at the same time. One had a broken rocker just like mine!

I've heard of this bike easily getting past 50k miles. Seems suspicious that it would fail after a rebuild. In my case, I was at 27k with the only engine issue being a coolant leak. I don't recall the milage or existing conditions on the other bike.

Could it be that the exhaust valve keepers let loose when the cam/rocker pressure is relieved?

My bike is going into the shop next week for an engine tick. I don't want this to happen again! Anything I should tell the shop (as much as I hate an amature like myself telling an expert how to do their job)? If Veronica blows up, it'll probably be a few years before I'm able to replace her!
 

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The keepers shouldn't be able to move until the valve spring is compressed and the valve pushed upward or held closed. But it is possible to put them in with only one groove engaged. Of course one keeper could break but it's rare.

I've seen it here and in looking through eBay listings. It seems to coincide with a period of storage or inoperation, so that made me think varnish or other buildup.

I suspected an intake valve sticking slightly on mine, it would sneeze out the left air filter shifting to second gear before warmup. But a lean condition can cause the sneeze, so I could've turned the choke off a bit soon. Anyway, I ran seafoam in the oil just in case.

Old fuel on valve stems can also cause sticky intake valves.

The ticking before warmup can be a sticky valve, because it allows slack between the rocker and valve stem. Should see a backfire, sneeze, miss, or reduced power.

Maybe the valve stem to valve guide clearance is a bit snug on this engine?
 
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