Lean fuel mixtures can burn valves.

http://www.ssch.com.au/trade-news/a-basic-guide-to-engine-valve-failure/

That valve did some dancing in there !

Maybe 2 causes, usually cam chain, sometimes stuck valve.
Normally you only see 1 valve busted, maybe rocker design, 1 arm maybe stiffer than the other.
Or lubrication/cooling, oil does both and oil does pool up some around the valves.
I don't think I've seen any burnt valves.

Serowbot wrote on 10/27/15 at 08:40:09:


From what I have seen on doing an internet search......postmortem analysis of these is nearly impossible.  The loose valve piece tears everything up and destroys any evidence of what happened first.

I don't know the exact number - but I have seen several damaged engines and heads on this forum or on eBay.  All of them have dropped one exhaust valve into the cylinder - I am not aware of any seats coming loose.

On some of the internet discussion about dropped valves, the cause is suggested as over revving the engine to the point that valve float occurs, and the valve does not follow the cam on the way back down.......and the piston hits the valve head.  Until somebody that was actually riding the bike when the valve failed comes along and tells us what they were doing when the engine failed......we are just speculating about how the Savage engine occasionally drops a valve.

I also just got photos of the rockers and cam from this engine.  With only 9,500 miles on the bike....how does this much wear occur on the cam and rockers?  This is the same damage to the cam and exhaust rocker that was on the bike I just bought....and it had 3,800 miles on it.  We can only guess that the oil the original owners were using did not have enough ZDDP in it.  Wonder if the cam wear and increased valve clearance can lead to valve failure?



 

I've always been told that excessively loose valves can be a problem because of the hard smack against the valve instead of the steady increase in pressure.

Not sure if it's true or not.  Never seen anything to back it up.

too tight and they don't close. Certain problems.. burned valves at best.
Too loose, noisy, and I suspect the smashing of cam into lifter/rocker allowed by the loose adjustment leads to at best, diminished performance, because thousandths of an inch are the differences between cam grinds and an adjustment that leaves several thousandths of an inch of lift for no reason other than being afraid to adjust them in the tight end of the manufacturers specs just doesn't make sense to me. I understand that the first time or two, but, once one has successfully been in and out, and it's obvious that reading, feeling, the gauges and getting TDC right, then push the envelope a bit. I have exactly nothing to demonstrate that the tight end of the specs is better for the cam, rockers and performance, but it's my opinion.