I have a 420 rancher with about 15hrs on it.Was wondering about adjusting the valves ....is that something that needs to be done??Will it hurt anything?

 

You need to adjust them at 20 hours (just like your owner's manual says!), which is right after everything is just nicely broken in. (If this is neglected, at best it will run bad...and at worst you can damage the engine.) Manual says every 200 hours after that...I do mine every 100 hours just to be safe.

If you are mechanically inclined, get a service manual and do it yourself. If not, spend the money to have it done by an experienced professional.