Uh oh. What did I do?

When you replaced the belt, you aligned cams and crank TDC, then removed the belt, and installed the belt starting at the crank, and routing it counter clockwise tight between the crank and cams with the slack all at the tensioner. You also ensured you have no slack anywhere except at the tensioner pulley, and pulled the pin on the tensioner so there was no slack anywhere. Looked to make sure you didn't lose any tension. Once you were assured you had good tension and everything was aligned, you turned the engine over at the crank a coupe times making sure your marks were still all at tdc. You also aligned the crank by the triangle, and not the circle at the crank. Once you ensured that everything turned without making contact, you attempted to start the car. Once you attempted to start the car you decided to loosen the belt? That is where I am lost. Assuming you did everything I mention above.

Do this. Remove the tensioner pulley. Remove the timing belt. Start by routing the timing belt around the crank work it behind the pulley and up around the front cam. Except this time take a breaker bar or wrench on the bolt and turn it clockwise a little. Once the belt is around it, put tension on the belt by turning the front cam counter-clockwise. Pull it tight, but not tight enough to move the crank. Look at your marks, and make sure they are aligned. If the belt is tight, and the crank and front cam are aligned, route the belt under the water pump and do the same clockwise to counter-clockwise on the rear cam. Turn the rear cam tight, but not tight enough to move the crank or front cam. Once you see both are tight and everything is lined up, install your tensioner pulley and double, triple check everything is tight, nothing is binding, all of your marks are aligned, and everything is routed properly. On the rear cam on the back side, the timing belt slips into place. You should be able to let go of the belt without tensioner tension and everything holds on its own without slipping.
Now that everything is correct, pull the pin on the tensioner. Make sure to turn the engine by hand at the crank clockwise at least 3 rotations going slow, making sure it doesn't bind to a stop. There will be resistance from the valve springs, but you shouldn't hear metal hitting, or parts where it is real hard to turn it.
Check your timing marks one last time before you try to start it.

You can verify the crank is TDC with cylinder #1 by taking out the spark plug and putting something thin and long enough to stick out of the spark plug tube. You want it to hit the piston head. Has to be skinny enough to clear the spark plug threads, but also straight so it doesn't get jammed when the piston raises and causes it to raise. So no grooves or steps on it. Watch it move up when you hit TDC on the crank. If it is not fully extended, you are not on TDC, and need to go back around. If you have a compression tester you can remove the pressure gauge, and put a balloon on the end of it, and watch the balloon expand. This is more accurate. This shows it is on the compression stroke. Make sure you do this to the #1 cylinder and not any of the others. Once you know the crank is TDC, the cams are only 1 way, so there is no need to double guess if they are TDC as long as they are at their marks.

BuckeyeTheDog said:

Oh boy. So how bad is that? Is that effectively the end of this engine?

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I'm dealing with bent valves myself on a odyssey I picked up for cheap. You have several options. Pulling the heads and having a machine shop fix them up $$$. You can replace the valves yourself, but it's a good idea to have a machine shop check your work. No telling what damage could have been done to the heads. I am currently changing my heads from a failed tensioner pulley that hammered the valves and the piston likely hammered on the heads through the bent valves. The valve head not seating correctly allowing the piston to transfer into the seat of the heads. At least that is what the pictures look like. I still have to open it up to verify. I ended up just going to the junkyard and searching for heads. I struck out 3 times before finding a decent one, and took me days and miles to get them, but only cost $180 total if you don't count the fuel and admission fees. Still no guarantee the heads you get will be good, and will want to have a machine shop look at them.
It's an involved job, and if you want to do it right, you will need new gaskets, head bolts, since you are removing so many things, you may be replacing broken (ones that you break) parts.
Another option would be a new-to-you engine. Either way you are looking at minimum $1K. If indeed this is what happened to you. There is a chance it is something else, but it's real hard to say without knowing exactly what it is that you did.
Was your timing off when you tried to crank it over? Did you have to re-align your marks?

I would research a lot before tackling the heads. There is a lot of little things to know. Such as do not touch the Head Gasket surface with your hands, measure Head Bolts to see if you can re-use. Torque difference between used/new head bolts, cleaning bolt holes, clean all matting surfaces without destroying them, and being able to remove all of the fasteners and their locations. It's a very involved job, and many pitfalls. The best tool for this job is knowledge, and 2nd would be prayers. There are a lot of things to get wrong.
I would do the compression tests. Triple Verify your timing belt job was 110% correct. This includes torqueing down all bolts, including spark plugs, aligning everything, and making sure it is indeed a bent valve issue from being misaligned, and your tensioner is full tension on the belt.
If everything is correct, and you are getting compression issues, pull your lower intake manifold, and you can see the intake valves. Check them real close for bent stems. This doesn't let you see the exhaust valves, but if you see bent intake valves, you will know for sure you have contact, and will need to replace the heads or engine. For some the engine is easier. Still a lot that can go wrong.