Originally Posted by Nano

As you know every precision built machinery has each of it's screws and bolts tightened with specific torques, that's why you have torque wrenches. Rc engines are not any different and using a torque wrench will always be better. If the head is not tightened evenly, the piston/liner alignement will not be optimal and you will get less performance and shorter lifetime from your engine.

If you are able to tighten the head screws with similar strenght for each of them, then you can work without the wrench. What is very important is that there is no need to tighten them a lot. Screw the screws and stop as soon as you feel resistance, eventually even unscrew half a turn and move to the next screw. Don't try to tighten them all the way in, you probably have to work on each screw 2-3 times before it's set, if you tighten one screw too far you will be out of alignement. Then for final tightening, I do it by only holding the screwdriver handle with the tip of my fingers and kind of roll the handle in my fingers (but I have pretty strong hands^^). If you grab the whole handle in your palm and tighten the screws that way, you probably are tightening the screws too hard.