Well, I haven't fortunately but its an expression heard occasionally on motorbike forums and I'm wondering if its a " thing" or just the result of poor maintenance (ie running with a knackered cam chain) and/or rider abuse.
My 24 year old DR350 with 27k on the clock is mid top end rebuild (pics to come of course!) and I'm wondering if its worth changing the valves at the same time?
Mind you a quick search and its £170 for the 4 valves, maybe that answers the question!!
The thing is if something goes wrong and the head gets trashed its game over for the bike so hence why I'm pondering this.
Any thoughts?
Dropped a Valve
Re: Dropped a Valve
without considering breaking belts,chains etc the most common reason for breaking valves is poorly adjusted tappets.So you are correct in thinking good maintenance should preserve your valves.But if you have them out you should get some paste and re-seat them.
Re: Dropped a Valve
In over half a million miles on bikes I have never had a valve fail. Some of the engines had a very hard life (young and daft) and hauling overloaded sidecars. As others say keep a check on clearances and you should never have a problem. The ONLY problem I bave ever had was when a cbx550 burned a valve out going to my father's funeral and that was caused by a very weak mixture due to someone tampering with settings just before we bought it. I hadn't had time to check it over properly
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paul_tim2000
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Re: Dropped a Valve
Only had it once, missed a gear change when racing my old Honda against a Guzzi LeMans down the A3 one sunday evening in the early 80's. Watched the tacho coming down from above 10K rpm 
Clattered down about 30 miles at about 30mph until the inevitable happened about 3 miles from home, valve stem sheared off at the top by the collet. Luckily it was all so bent that the valve couldn't drop into the cylinder.
New valve and guide, engine ran just as well/badly as before the whole incident.
I do know that in the early days the welding of the valve head to the stem wasn't as controlled as it is using modern manufacturing methods and there were examples of the assemblies breaking, usually when tuned and raced. I suspect that 'dropped a valve' became the go to excuse for poor tuning and preparation both on road and racetrack.
Clattered down about 30 miles at about 30mph until the inevitable happened about 3 miles from home, valve stem sheared off at the top by the collet. Luckily it was all so bent that the valve couldn't drop into the cylinder.
New valve and guide, engine ran just as well/badly as before the whole incident.
I do know that in the early days the welding of the valve head to the stem wasn't as controlled as it is using modern manufacturing methods and there were examples of the assemblies breaking, usually when tuned and raced. I suspect that 'dropped a valve' became the go to excuse for poor tuning and preparation both on road and racetrack.
