Replacing a bicycle drivetrain. Bike frame cracked. Unpredictable end

In our bicycle workshop, today we have a mtb bike with the task of changing the drivetrain.
I will show you the main signs when you should replace the drivetrain on your bike.
How to accurately diagnose a bicycle chain for wear and stretching.
You will see how you can determine that a bicycle cassette has already exhausted its service life.
On the client's bicycle, we will change: the cassette, chain, bike cranks, and we will also need to replace the bicycle bottom bracket.
The bike bottom bracket also requires replacement, as it makes additional noise when rotating.
New bike cranks have a different seating depth during installation.
At the very end, there will be a moment unexpected for me)
Bicycle frame to be replaced)
A video that relies on technical sounds rather than speech. Language-neutral; designed for international audiences. Presented as a DIY tutorial.
Those who are into bicycles will find this video a treat.

00:00 How do you know when it's time to replace the drivetrain?
00:38 How to check the tension of a bicycle chain.
01:17 How to determine the wear of a bicycle cassette.
01:42 Bicycle cassette wear measuring tool.
02:42 How to change a bicycle cassette.
03:54 Installing a new cassette on a bicycle.
04:21 How to remove an old bicycle chain.
04:52 Unpacking a new 8-speed bicycle chain.
05:49 How to determine the elongation of a bicycle chain without a special tool.
06:23 How to quickly remove bicycle pedals.
06:51 How to quickly remove bicycle cranks.
07:40 How to choose the right bottom bracket for new bike cranks.
08:51 How to quickly remove the bike bottom bracket.
10:29 How to choose a new bike bottom bracket according to the frame size.
11:09 Unboxing the new bike bottom bracket shimano.
11:32 How to clean a bicycle frame in the area of the bike bottom bracket threads.
12:15 Bike frame cracked.