Well, loads of people said it would be a nightmare, I should leave it to the pro`s, that I would need special tools etc etc, so just to prove them all wrong, I fitted it myself this morning. It only took me 2.5 hours too!
Frankly, I found it very easy to do. Put a little thought into it, take your time and it will be fine.
The haynes manual for an Omega gives details about the belt fitment, and whats written below should help you adapt this to a calibra.
Jack up and support the car and remove the drivers-side front wheel. Remove any splashguards in the wheel arch.
Get a 2nd jack under the sump with a block of wood to spread the load, and gently support the weight of the engine.
Remove the airbox and trunking to the throttle assembly.
From underneath, remove the drivers-side lower engine mount. 5x 15mm bolts hold it onto the chassis and engine.
From above, remove the engine steady bar. 3x 15mm bolt hold it to the engine and a long 15mm bolt passes through the other end of the bar.
Use a spanner on the aux drive belt tensioner to shift it clockwise, allowing the belt to be slipped off the wheels. If you arent confident in your memory, sketch its route to aid when re-fitting as it is quite convoluted!
Remove the tensioner wheel, power steering pump wheel, and the water pump wheel. The tensioner is a single nut, the others are 3 little bolts.
I found the water pump wheel wouldnt fit past the inner wing, but using the jack to raise the engine slightly allowed it to come free. A 1.5inch spanner was handy to prevent the pump spinning as I undid the bolts. I locked the PAS pump wheel by jamming a screwdriver through the holes on the wheel while I undid the bolts.
Remove the crank pulley wheel, its held on with 6 torx type bolts.
4 torx type bolts hold the timing cover in place. Its a bit of a pain to jiggle it out of place, just make sure you havent caught it on anything as you pull it out.
Use a big torx socket on the crank pulley and turn the engine to TDC on no1 piston as detailed in the haynes book. Make sure all the timing marks line up.
At this point you are supposed to use the Vauxhall special tools to lock the crank and cams in place. I decided to improvise....
2 small pairs of mole-grips are perfect for this job. Dont put them on too tightly as you may distort the cam pulleys or possibly bend the cams, they just need to be tight enough to prevent the pulleys turning.
I didnt need anything to lock the crank, I was just carefull not to pull it out of place when removing and installing the belt.
Doing the timing belt itself is detailed perfectly well in the haynes book. Follow it step by step and you will be fine.
If you are replaceing the idler wheel too, I found it easier to thread the belt into place, then fit the lower idler last of all.
I found a little wedge of wood was great for holding the new belt in place on the bottom pulley as I threaded it up around the other wheels.
A 30mm spanner(i think it was 30mm!) is needed to turn the idlers around their offset mountings to take up the slack in the belt.
After I had turned the engine over by hand and re-checked the timing and tension as detailed in the haynes book, I unplugged the multi-plug connector on top of the DIS module so the engine would not run, I then turned the engine over with the starter motor for a while, allowing the belt to settle into place. I found that after doing this the tension needed adjusted again.
In the great tradition of haynes, re-assembly is a reversal of the dismantling process!
Remember to tip the engine slightly with the jack to get the water-pump pulley back into place, and everything fits back just as it came off.
Once its all back together, stand back, crack open a beer, and feel proud that you didnt have to pay over £300 to get this done at a garage!
BTW, I got the belt, tensioners and idler wheel as a kit from AutoVaux for £77+vat.