It is easier to have someone else replace the timing belt, and the cost is usually reasonable - it is a very common repair. However, after reading the newsgroups for a couple of years, as the mileage for change approached, I leaned toward doing my own work, and wound up actually having no problem because I was prepared. I enjoy things like seeing the oil pump gears and discovering the clearances are excellent I do have a spare vehicle though - that might make a difference. I did not finish in one day, but . . . I did some other work also (replaced engine oil pan gasket and transmission pan gasket). To me that's one of the benefits, you can take the labor charges saved and replace more parts like the missing timing cover gasket sections. There are a couple of reasons you might want to do your own repairs.
1) It can be very rewarding to understand how everything goes together.
2) The owner can often take more time than the mechanic paid by job or hourly rate. For example I clean every bolt and surface thoroughly prior to re assembly.
3) Almost without exception, every time I do work that has been previously done by another mechanic I find errors were made. For example during this work, I found two stripped transmission pan bolts, a chipped crankshaft pulley (from prying instead of using a puller), thermostat installed incorrectly (jiggle valve), any many components over tightened. If you're careful and understand what you're doing, you may actually do a better job.
My notes:
6/12/04: Major Servicing: 120,124 miles: Replace: timing belt, crankshaft oil seal, oil pump oil seal, oil pump O-ring, camshaft oil seal, idler bearing, idler tensioner bearing, timing cover gasket set, valve cover gasket, ck valve clearances, PCV valve, PCV valve grommet, oil cap gasket, distributor O-ring, distributor cap, rotor, distributor packing, spark plug wires, spark plugs, fuel filter, air filter, ck. battery, oil pan gasket, transmission pan gasket, water pump, thermostat, radiator cap, gas cap, differential service, engine moving control rod, accessory drive belts: power steering pump, A/C - alternator, alternator brushes, ck. chassis mounting bolt torque, set ignition timing =============== I would say the sticking points where the tricks of the trade can help a lot are
1) removing the crankshaft bolt - I used an electric impact gun - later acquired air powered
2) removing the engine brace - secret: do this after removing the crankshaft pulley so you can reach bolts from beneath - makes it much, much simpler
3) camshaft seal - the cam turns at one half engine speed, so this seal wears more slowly, but is helpful to have the special installation tool I purchased which makes installation a breeze
4) belt tensioning - you need to replace the tensioning spring with new, but do not rely upon that spring - you need to loosen the tensioner bearing and exert a lot of force to tension the belt. I used a hook tool to pull up, you could also use a pry bar. After exerting lots of pressure to pre-stretch the timing belt, then release it letting the tensioning spring maintain the correct tension as you tighten the tensioner bearing. Most people will have others work on their car, and that's perfectly fine, but my Camry is actually improving over time with increased smoothness, power and comfort over prior years as maintenance and repair work continues - replacing the axles and brakes for example. The first item I replaced was the radiator. So as you do more, you learn more. I do not believe, generally, the four cylinder Camry is difficult to work on, as long as you go step by step and work carefully. I do recommend getting the factory service manual set though - have found it very authoritative, helpful, and easy to follow. Keep checking eBay.