I bought a new 05 Grizz this past summer and have already put about 350 miles on it and have about 30 hours. Reading thru the owners manual it recommends that you adjust the valves at 20 hours. I've already changed the oil several times, but is it really that necessary to adjust the valves if there not making any noise? Also, what tools does it require to adjust the valves and is it something I should tackle myself or just take to the dealer? I've ringed my Banshee before, but I've never worked on an atv with valves. Is there any other maintainance I should look into right now? How often should the gear oil be changed?

 

Most likely the valves wont need adjusting, but they should be checked. If they got too tight...it would be quieter than normal, so you cant always go by the noise.
Theres a few websites with a how to on the grizz, check on nyrocs and texmudders sites.
The gear oil is good until water or dirt gets in it. So if you go mudding, and you think it got contaminated, then change it. The differential lube in cars and trucks lasts well over 100k miles, and its the same stuff in the quad.
Its just simple hand tools, and feeler gauges, and it takes longer to remove the fenders and other stuff, than it does to adjust the valves. Just be sure to set it on the correct tdc, its the tdc of the compression stroke, and not the top of the exhaust stroke.

 

Some of the guys I talk to adjust thier valves at every oil change, or every 50 hours.
The grizzly engine is the same as the raptor so this link should help you out. valve adjustment.

 

Adjusting valves can easily be done yourself. It takes more time taking everything off to get to them than it does to actually do the job. Best advise is buy a Clymer or other maintaince book (about $20 cost) for your Quad it has very detailed intructions on anything you can do to your quad. Only special tool you should need is a feeler guage which i got at sears for $10 bucks or so. Not sure if its just the yamaha 350's but i find on my warrior and big bear the intake valve is usually fine but the exhaust valve gets off pretty quik.

 

To answer your question, yes, it's very important to have your valves checked and adjusted if necessary, expecially on the break-in. It's not hard to do if you know what you are doing but it's easy to screw up if you don't know what you're doing. Personnnaly, I take mine to the shop but I have a mechanic that is very good and I trust him. It doesn't take him any time at all to check and adjust them and I don't mind paying for it as well as the piece of mind knowing it was done right.
If you want to do it yourself you should at least have someone help you that has done it before. The biggest mistake people make is adjusting them on the exhaust stroke instead of the compresdsion stroke and then wondering why it runs so bad when they are finished.