Hi Kevin,
The process varies from one ATV to another. Some require you do the adjustment when the motor is cold, some require that you run the engine to normal operating temperature, then do the adjustment.
The gap between the rocker arm and the end of the valve is the point of adjustment.
You would need to rotate the engine over by hand so that the "gap" is at its largest point, this is usually near TDC (top dead center), but can vary from one machine to another.
Once the engine has been turned to the correct position, simply insert a feeler gauge into the gap, and adjust open or close to reach the correct gap.
Some also refer to this as the valve "lash".
There needs to be a gap so that the surfaces are not always wearing against one another. This would case the rocker arm end, or the end of the valve stem to wear out prematurely, not to mention the possibility of creating metal flakes or shavings being dumped into the oil system, causing major problems with the other engine components.
Unfortunately, I do not have the gap setting for you, you should be able to get that from a local honda dealer. Once you have it, call another one to verify the info is correct. This is worth the price of the phone call, even if it is long distance...
The best way to know everything you should about your ATV is to purchase an ATV repair manual for your machine, this way the info is always at your fingertips. If you are interested, here is a link to that page at the
ATV-411.com website
TRX 450 repair manual
I hope you find this info helpful, thanks for visiting the site and the forums.
Should you need any parts, please visit our vendors, here are a couple of them to check out...
RideGear.com
ATV Tools and Manuals
ATV parts and accessories - JC Whitney
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