Lets say you just rebuilt a very trick Yamaha single( like 686cc watercooled) and you got the mechancial timing off by one tooth(there is a mark on the cam sprocket and you put it on the one next to it). Could that be enough to cause a valve to hit the piston and make big boo-boo? Semi-hypothetical question, but something I'm curious about... Thanks in advance for your intelligent responses.
I agree, but it is not a "given". Yes it is possible, but depending if it is off advanced or retarded there is a chance of no damage being done. JMO Tdub
Get it timed right and do a compression check and a leakdown check. Knowing both of those will tell you if you have a problem or not.
If it's lightly "tipped" a valve, the valve spring pressure may be strong enough to pull the valve/s into contact with the seat/s allowing for normal compression test results. Slightly bent valves will work fine until they work harden and the head/s pop off and trash the top end. If you felt a hard spot while barring the engine over, pull the head, remove the valves and measure them for run-out. It's a pain in the ass but much better than lunching the entire engine a few miles down the track AND you will sleep better having double checked for damage.
The answer Franz is a HUGE depends. How radical are the cams? Head decked? Where are the cams degreed in the sprockets? Bunch of stuff. Simply boils down to piston to valve clearance as the piston approaches top dead center. And if that piston to valve clearance is enough to allow a valve to be open by how ever many degrees one tooth makes. On some bikes theres enough room for the bike to crank up and run and never ever hit a valve but just be down on power. On others (for example a race motor with the cams degreed so they're rolled out far out as they can go to make a top end motor) then there's absolutely no room and it would suffer catastrophic damage on the first revolution. So the answer is and only is: depends. Do I know this bike?
