The timing belt on my 99 kia sephia has apparently broken...is there any way to tell whether it damaged the pistons and valves before I spend money replacing the timing belt and water pump?

Maybe you broke your timing belt. My kia did that driving fine, then all of sudden nothing. If you don't change a timing belt at every 40,000 miles you're taking a chance of breaking then slamming your piston into valve. Messing up up the top end of my motor. No compression. If you have a compression tester. That would tell you alot. Good luck. Hope it is not that.

No compression and no start with a cam sensor code makes me think that you have a broken timing belt. If true, there has been some engine damage. The pistons will hit the valves and cause bent valves/ holes in pistons.

it is an interference engine which means that when a belt breaks , you can expect at least half of the valves to be bent and need replacing
you can get more quotes for the job as that seems extreme
the work entails replacing the belt , idler pulleys , cam and crank seals and hydraulic adjuster ( a professional job to get another 60,000miles from the belt)
That much will set you back by around $1000.00 including labour
The extra is the head removal and new valves so add another $700.00 --including labour )for that and you can see that you need more quotes from accredited service shops

Most manufacturers say 100,000 miles. It is something that should be done before then, I believe; because engine damage can result from the belt breaking, and it will leave you stranded. The timing belt is not something you should attempt, unless you have engine mechanical experience. If you don't, I recommend that you get it done at a shop as soon as you can afford it. $700 is a lot of money, but a possible engine replacement and a tow is a lot more!

yes you do need the work doing ,new head gasket and at least 3/6 valves bent

It's not that bad of a job to do, but if your timing belt has gone bad. more then likely you have piston to valve damage, this is an interference engine, which will cause internal engine damage.Belt should be change out every 60,000 miles.

Yes this is and interference engine and will be damaged if you were driving when the belt broke more than likely.

Be sure to pull out the plugs and turn the motor over 2-3 times in the correct direction in order to seat the belt, then line up the marks and check. If the belt broke or jumped a tooth to prompt the belt to be changed in the first place and it wasn't done as a routine maintinence repair then the car may have a bent a valve because these engines are what's called interference engines this means that the valves operate very close to the pistons so if the belt broke or jumped a tooth one of the valves may have been left open a bit as one of the pistons came up a hitting it. This scenario is common with people who allow the car to go more that 100,000 - 120,00 miles or more without doing the timing belt as a precaution, in your case I hope not.

You need a timing light and a new belt

If your timing belt came off when the motor was running, there 2 possible scenarios:

Motors are interference (pistons hit valves if motor spins <=2 revolutions without a functioning belt/chain) or not.

1. if kia 1.8 motor is an "interference" engine ... major damage already occured, at best valve stems are bent and you have to pull the head to install new valves, at worst, a piston now has a hole in it and you get to do a full rebuild.  I'm now praying for you;~).

2. if it's not an interference engine ... joy is you,  you rotate the cams whichever way you want and pistons do not hit valves ... and as they say in England "Bobs your uncle" ... ask a Brit.

I'm guessing that Kia doesn't build an interference motor with a belt ... the dealer or any shop with access to a good paid automotive database can tell you if the motor is interference or not. 

The standard explaination for rotating forward ... which is not necessarily clockwise, has to do with tensiong the belt and how you get the tensioner in the correct position to do its job ,,, which is to keep the timing belt from jumping teeth.  Each motor can be slightly different for tensioning the belt, so you need the specific instructions for your year car with the 1.8 motor.  If the manual says you need special Kia tool "XYZ" ... get it or an close equivalent, don't try to use a pair of vicegrips clamped to a  screwdriver. 

You need to spend $20 for a Haynes manual for your car.  Now you or I might think for a minute that what they say in the haynes manual isn't the easiest way ... but then we would probably be wrong. 

Having done several timing belts, engine rebuilds and general maintenance over the years ... I can tell you this sincerely ... advice from someone (haynes in your case) who has actaully done the job you are embarking on is worth more than $20 if you are doing a job that takes more than a couple of hours.  The specific stepwise instructions they have will get you successfully to the place where you have a new timing belt and the motor runs right by the shortest path.   And one of the biggest benefits in doing a job of any complexity, it that you have written stepwise reassembly procedure documented ... so you don't end up at step 17 in the reassembly ... just to realize you didn't do step
9 .. that now requires to take stuff apart for the second time !^%$@!

Good luck ... you'll feel great when the thing is purring again.

..ajm