1hz timing belt, motor won’t turn by hand

Mate it sounds like the pistons are hitting the valves because the valve timing is out. You need to slacken the belt tensioner, remove the belt & get all the valve timing marks on all the cam belt pulleys crankshaft, etc in their correct positions. The pulley marks usually consist of what looks like a big centre punch mark on the front face of each pulley on the flat face next to the pulley teeth. Those marks in turn line up with other markers on the fixed part of of the engine like an arrow or similar. When you have the marks all in their correct static positions, have a look at the belt OD & there should be some straight white lines going across the flat face of the belt. These are your belt timing marks which in turn line up with the pulley timing marks when the belt is fitted in its correct position. Fit the belt, let the belt tensioner do its thing, then turn the engine by hand two full turns, firstly to tension the belt & secondly to make sure you don't have the problem you have now. On no account start the engine like it now or you will in l liklehood finish up with bent valves & damaged pistons & a whole world of pain that you are trying to avoid by correctly doing your preventative maintenance before the belt breaks.
TIP: NEVER attempt to turn the camshafts by the bolt head that holds the belt pulley on to the camshafts.

Hand crank it back to where you started and check the alignment again. Here's the manual if it helps,
http://repairmanual.free.fr/_1PZ_1HZ_1HD-T_engine.pdf
Remember that just because the marks line up you may not have No 1 cylinder at top dead centre, you may be one full turn out!

Nicholas,
Did you crank the engine with the starter with the old spring? If you have previously answered this I must have missed it.

If you had everything lined up ok the spring would have made no difference, it was working well enough before you did the job it should still have enough tension to do a test turn although the starter isnt a wise way to do it.

If the valve timing was far out you should have noticed a very different noise while cranking.

If you have never turned a diesel by hand they are bloody hard to get through compression compared to a petrol engine.

If it is your lucky day this might be all it is.

These motors are interference motors, the front crank pulley marks are not top dead centre but bottom dead centre, this is so all the other marks line up and the belt can be changed/safe to move the cam away from piston contact with valves. If you have used the starter, start planning to take the head off. If you havnt, loosen all the bolts that hold the cam to the head, do it evenly. This will close the open valves and allow you to turn the motor back to line the timing marks on the crank harmonic balancer. If it is on no1 bdc, the marks on the timing belt cogs will be in the correct place. If not, turn 180 degrees and check again. Do up cam, check key is not sheared in belt pulley and try again.

Any updates?