(This isn't a DIY in the sense of step-by-step instructions. Mods feel free to move or delete)

First off, consider carefully whether it is even worthwhile to change the head gasket. It's a huge undertaking. It might be easier and less expensive to change the whole engine for one with fewer miles and fewer problems. I didn't do that because I worried that that would be exchanging known problems for unknown ones. The replacement engine might be in worse shape than the one I have. It might even have the same head gasket and stripped head bolt holes problem.

Also consider whether it might be more cost-effective to just junk the car and get a newer one. I didn't do that because now (late 2021) is a bad time to be buying a car, what with the global chip shortage pushing prices up for new and used cars.

Also consider why you want to change the head gasket. If you stopped because steam was pouring out from under the hood, or because it smelled burnt, or because you looked down and the temperature gauge was pegged, you probably shouldn't bother. You've probably cooked that motor good, and there's a better than even chance that changing the head gasket won't get you that many more miles out of it, if any at all. I only stayed with the motor I had because I knew I hadn't overheated it. I first noticed that it was blowing coolant overboard through the reservoir vent, but I thought it was maybe a bad radiator cap. But I started monitoring the engine with OBD2 and the Torque app, and set an alarm for a coolant temp of 220F. And when the alarm went off, the dashboard gauge was only a tiny bit above its normal spot, and it was the first time I had ever seen it above normal. I immediately shut the engine down, waited for it to cool, and reloaded the radiator with coolant.

Also, if your motor is a 2006 or earlier, or even an early 2007, you should fully expect to find the threads for at least some of the head bolts in the aluminum cylinder block to be stripped. If you're a cheapskate but have good machining skills you can probably just helicoil them. But if you want to do it right you should get the Timesert or NS300 thread insert kit. Expect to spend about a half hour doing each of the ten holes; five hours total. Others have said that the ones most likely to have stripped out are the middle three in the back row. But on my motor two of the ones in the forward row were stripped as well. So my advice is, if any of the holes are stripped, just do thread inserts on all ten. Buy the kit, watch the YT vids, follow the instructions in the kit to the letter, and it will go fine.

Also, even if it seems that none of the holes are stripped when you take it apart, don't expect the threads to survive reassembly. That happened to me. I had replaced the head gasket and put the head back on, and was torquing all the bolts up in stages. They all got to 25 foot-pounds just fine, but when I was taking them all up through 35 foot pounds, one of the ones in the back row suddenly went to zero foot pounds and spun easily. And when I was taking it apart again one other in the back row and one in the front row came out of their holes with the aluminum threads from the block. If you're in any doubt, just do the thread insert kit.

Be warned that the underhood packaging is so tight that this job is just barely possible without removing the motor. If you have large hands, it might not be possible for you at all. But understand that the things that make this job hard are mostly the things that make the tC such a nice car. It is a small and light car, but with a fairly large engine as four-cylinder motors go. Those make for a sporty car, but the inescapable side effect is that it makes for tight packaging and poor maintenance and repair access.

I won't give you the step-by-step instructions, you can get that more authoritatively from Alldata with all the torque specs and everything. Just pony up the $20 for a one-month subscription, download at least these three procedures, and any other you think you might need:

* Cylinder head removal
* Cylinder head installation
* Timing Chain installation

Some random thoughts on doing the head gasket job:

* I don't know, but it may be possible to remove the head without removing the timing cover, if you remove the top two horizontal 6mm studs that hold the timing cover to the head. There is a guide below the timing chain sprocket on the crankshaft that prevents the chain from disengaging the sprocket. If I had known that before starting, I probably would have tried removing the head without removing the timing cover (and motor mount and water pump and lots of other stuff). But again, I wasn't adventerous enough to try it. If you do try that, you will certainly have to remove and reset the timing chain tensioner. You will also have to re-time the cams without the benefit of the painted chain links.

* Special tools: In addition to the usual metric wrenches and sockets, you will also need:
--10mm double-hexagon wrench for the cylinder head bolts
--E-type Inverse Torx sockets to remove 6mm and 12mm studs

* If you don't have access to a dry, well-lighted work area, this job would be huge hassle. I can't imagine doing it on the street or in a driveway.

* Expect it to take four or five sessions of about 6 hours each. There is a lot of stuff to remove, and the same amount to put back on.

* The hardest bolt to remove is the one for the crankshaft pulley. I used an air impact wrench to remove it and later to reinstall it.

* On the intake manifold, in addition to the three bolts and two nuts that hold the manifold onto the intake ports on the head, there are two more bolts down along the bottom of the manifold on the back of the motor. You have to crawl under the car and reach up through the subframe to get these bolts. They are a bit hard to find and harder to reach.

* Every time you remove a set of bolts or a small part, put them in a labeled baggie, and number the baggies in sequence to make it easier to reassemble things in the right order. And there is indeed a right order.

* While you have everything apart, consider replacing the water pump and the serpentine belt tensioner. I replaced the pump because it had telltale signs that it was leaking a tiny bit, and I replaced the belt tensioner because it was starting to sound a bit like a rollerskate wheel, and I might as well do it while I was in there.

* Take lots of cellphone photos as you take things apart. I wish I had taken a photo of the little metal channel that protects the crank position sensor wire from all the whirly stuff around it. It took four tries to find the right way to put it back in so that the alternator would fit back in.

* While the cylinder head is off, be very careful about the cylinder block deck surface. The cast aluminum is not all that hard, and a heavy wrench dropped on it can mess up the sealing surface and make it leak.

* Be absolutely as clean as you can while working. Stuff rags down the three holes in the deck that drain oil down into the pan, and put earplugs into the two oil gallery delivery holes. Cut long strips of rags from a sheet or something that you can stuff into the water jacket. When reassembling, check and double-check that you have removed all the rags and plugs.

* When you are doing the threaded inserts for the head bolts, you will do a lot of drilling and make a lot of chips. Do everything practical to keep the chips out of the engine.

* Every time you put in a bolt, be careful that it starts cleanly into its hole before you start wrenching on it. This job is hard enough without having to repair stripped holes or broken-off bolts.

* Be sure to put the crank position sensor wheel back on, and in the correct orientation. There's a big F on it for Forward in the sense that the pulley end of the crankshaft is the front of the engine. If you can't see the F then the wheel is on backwards.