Great Article by Dan!!
http://www.dansmc.com/valveclearence.htm
Valves ? I have no problems... mine are nice and quite. Maybe and maybe not. As we know, metal expands and contracts as it heats and cools. Because of this there needs to be some clearance for the metal to expand into. Sometimes it's a little and sometimes it's a lot.
So what happens if there is too little clearance ? Well, for one thing the valve loses most of it's heat through the valve seat. If the valve doesn't seat fully it will start to get hotter and hotter. Sooner or later the valve starts to melt or burn. Not good ! Now if the clearance is too much the valve train components will be hammered every time the valve opens. Again, not good but better then too hot.
To prevent these problems some engines use hydraulic tappets which pump up with engine oil while the engine is running and keep the right clearance. The newer Honda Gold Wings have them and so do the Honda and Kawasaki V-twins. Harley-Davidson Big Twins have them too, not to mention others. Now for some reason everybody thinks valves loosen as the miles pile up but they don't, at least they don't unless you have lubrication problems. ( So change your oil, OK ? Well, at least check it now and then... maybe ? ). If an engine is running and click the link below to get all the mind numbing info!
http://www.dansmc.com/valveclearence.htm
