why do the 5 valve yamaha's need less adjustments over a given period of time/running compared to a 4 valve kawasaki or honda? especially the honda crf's which are prone to valve issues. that motor only makes about 10 more horsepower than the klx yet they've had huge problems with the valves whereas we have had pretty much none. why is that?
i understand that those bikes spend more of their running time up in the 7000 to 10,000 rpm range but shouldn't honda have engineered the motor to be able to survive up there.
between the valves and pistons and rebuilding the heads it appears as though when you buy honda you have to expect to pay as you go for the life of the bike. with our bikes you just ride and every now and then look at a few things then go right back to riding.

i sound like gump here but i'm looking to get a new bike and these are some of the things i've come across in my search. Thanks for any help/advice you all might have

 

Take a look at how how Honda's camshaft is in relation to the valves theres your difference. Yamaha runs lighter seat pressures due to design thats how they get extended service intervals.

 

ok thanks. i'll look at some schematics to understand what your saying.

 

Just guessing here, but probably with 3 intakes instead of 2 they can get away with opening the valve a lesser amount which might not need as stiff of a return spring and result in less slamming of the valves against the seats, resulting in less stretch and thus fewer adjustments. I'm probably talking out my butt though since I really have no idea.

Could be valve material, in part, also. Some high performance engines use titanium valves since they are lighter and can be opened and closed faster = faster revving engines. But titanium will not hold up as well as stainless steel. On the other hand stainless steel is heavier and will require stronger return springs and if everything else is equal, won't allow the engine to rev as high and as quickly. Generally if its got titanium valves, you'll need to adjust more frequently than stainless. And they are a lot more expensive to replace also.

 

The valve seat material plays a part in the service life too. That's also directly linked to the valve material. The biggest problem with the new high performance 4 strokes is dust. So keep those filters clean and oiled boys and girls.