I am new to riding motorcycle. And I tend to use my legs a little forcibly while changing gears. A friend told me that this would cause the gearbox to wear out soon. He suggested me to do it gently such that it wouldn't make any sound. I am trying to do this right, but the sound always comes no matter how gently I press the gear. Is it true that this behavior can cause damage to gearbox or is it just a myth?
I read a book called Engineer to Win by Carrol Smith. In the book he talked about the amount of stress any piece of metal can sustain before failure. He described how, for instance, a valve spring can handle many, many, many, revolutions of the camshaft as it bumps the valve train. It can deal with this over and over again as long as the lift of the camshaft doesn't exceed the designed limit of what the spring can handle. As long as the spring is operated within its design specs, it can virtually last forever. If the camshaft is changed out for one with a larger lift, which exceeds the design of the spring, the spring's life expectancy goes down dramatically. The larger the lift, the sooner the spring will fail.
How does this apply to what you are doing and experiencing? While banging the gears, as you are doing is probably not going to cause any noticeable damage right away, the more you do it, the sooner some part of the shifting mechanism or transmission is going to fail (either the lever, a gear, or whatever). It may be more fun to drive your bike by banging the gears, but do you need to do it to accomplish the gear shift? If not, you are causing undue wear upon the parts. Your banging the gears could cause stress risers to form, which, over time, will cause a part to fail. I would suggest your friend is spot on.
When you change gear you don't use your whole leg to change from one gear to another. You should be able to just use your foot and ankle without moving anything above your shin.
If you have to move the whole leg to change you should change the position of the gear leaver so it is closer to your foot.
To do this there is usually a bolt on the gear leaver that you can loosen off and then change the position of the leaver. Make sure the bolt it placed back on and fastened tightly.
In-regards to sound when changing gears this depends on the type of bike you ride. On my KLX 250 there is no issue with gear changes but guaranteed on a Harley Fatboy there will be a bigger clicking noise when changing into gear.
Easiest way to find out it to ask a dealer how much noise there should be between gear changes. They might tell you there should be nothing or that it is the nature of the beast
You will get better at shifting with time.
@willNz is correct, this is dependent on the brand of bike. Therefore, difficult to definitive answer.
Something you should check is to make sure the clutch is adjusted properly and the gearbox has the proper level of lube. Those two things can cause noisy shifting no matter how gentle you are. Cables stretch and parts wear, so it is amazing what a little adjustment can do.