if you are talking about adjusting the gear mesh (space between the clutch bell and the spur gear).
yes, you must loosen and remove the engine screws and apply blue loc-tite to them.
as far as i know, the gear mesh does not come set from the factory on any nitro r/c so you're best bet is to set it using the sheet opf paper method.
you want to feed the paper in between the gears, and then come back out with the pattern of the gears imprinted in it. the paper will look wrinkled, have a zig-zag pattern and should not be torn when the mesh is right. feed the paper in between the gears, slide the engine over towards the spur gear, and turn the clutch bell to make sure that it isn't too tight on the paper. you should be able to turn the clutchbell with your fingers and the paper should be snug between the 2 gears. snug the engine screws a bit, and check the paper again. it usually takes a few tries the first time because you may not be sure exactly how it should feel.
i would remove all 4 engine mount screws first and put loc-tite on them, put them back in loose enough so that you can still slide the motor.
set the mesh with the paper, and tighten the screws. double check the mesh after you have tightend the screws because sometimes the motor will move a little when you fully tighten the screws down.  you may have to try and set the mesh 4-5 times before you get it right. it may keep ending up too tight or too loose when you tighten the engine screws. just have patience, and always double or triple check it with paper once you get the screws tightened down.
correct gear mesh is very important. it means that you may only be able to run it once and chewing up the spur gear if the mesh isn't right, or running it for a very long time on the original spur gear.
I'm still on the original spur gear in my volcano, and i just cracked open my second gallon of fuel.
you should check the "how to" videos here...there may be a video showing how to set the gear mesh with paper.
that way, it will give you a visual to make it a little more understanding.
hope this helps you out.