I bought a haro flightline two dx and i want to upgrade it (fork,brakes,derraulliers,...)iam scared that if i do this with this bike that my fork is going to fail or something like that so could i do this with a 100mm sr suntour xct v2 or could i upgrade it to a fork with more travel. I dont know if a fork with more travel can go on this bike.Will my fork fail?and can I upgrade my bikes travel?
It looks to me that the bike is an entry level XC mountian bike. Not a great bike, at the right price tag, none the less suitable for off road use. I wouldn't take if off a 2 meter drops all day, but it should be OK over less than about 300mm (1 foot) and more if you know how to land. If you keep the wheels on the ground it will handle most tracks.
Upgrading the fork to more travel will change the geometry. Too much is a bad thing, but 20mm or so should be OK. Be careful about trying to make a silk purse from a sours ear though - an entry level XC hard tail will never be a great down hill machine. Looking at the list of upgrades, it would be better to start with a bike closer to what you really want.
As for breaking the bike etc - it will probably not fail catastrophically from normal riding, but it's not a 20kg downhill tank, and parts breakable if abused. Riding style and skill , as well as your weight, plays a part. A skilled rider controls the bike over the bumps and landings, and rides "lightly" and unskilled rider can land very "heavy" on the smallest bumps and jumps.
Theres nothing wrong with a hard-tail for down hilling - not that many years ago people rode no suspension on what we now consider "Light" down hill tracks (I used to land 2 meter jumps with no suspension, ....memories... the early 90's, just like life, MTB's were so much simpler - 2 wheels, 18 gears, choice of steel or steel frames and one size nearly fits all..... ),
Although this one would not be my choice, if it's all you have got, get out there and have fun.
Yes it is OK.
Since you are just starting out you need to focus on the basics of riding (proper stance, cornering, braking etc) which will allow you to ride better, faster and safer. And generally focus on having fun.
Don't waste too much money on that bike. Just use it a lot and maybe switch to a better bike in a year or so.
Not so long ago, 80mm would be a DH suspension already. Then the 100mm ones came and the whole DH community was stunned by so much travel. So, considering travel alone, 100mm is enough to do what you want. BUT you have to consider two more things:
At last, the frame should be compatible with longer forks. I've seen people installing double-crown, long travel forks in "regular" frames and go downhill, and eventually the head tube was torn off the bike due to excessive lever from the front wheel while braking and landing.
Hope this helps!