I replace the head but i dont know what position I have to put the camshafts to install the cam gears

take a look at the image I attached and see if that makes sense

Roy

yea its like the pic.so what is the position of the camshaft at this point

tdc which is what you need. the crankshaft has to be at tdc as well, then you install the belt and hand rotate 3 times and verify the marks are still good.
be carefull, if you do not install them correctly, you will bend valves.

Roy

ok.and before put the camgears and timing belt what should be the position of the camshafts??because I tried to put it on one place but I think it needs to be on a specific position. or not??all this before install camgears

the cam should have a key way that allows the gears to go on 1 way. make sure the correct gear goes on the correct cam as in the picture. do not rotate the cams with the motor at tdc as you may bend a valve.

Roy