Hyundai Repair: cylinder head, internal combustion engine, stroke internal combustion

Question
Hi.  I brought my 2004 Kia Optima (77k miles) to Midas for a timing belt replacement.  Apparently the new timing belt slipped off while they were testing it and the engine was severely damaged.

The manager was very apologetic and has offered to repair it at no cost to me and they put me in a rental car.

I just want to make sure they do the right kind of repair and don't cut corners to save cost.  The manager told me 2 cylinders are cracked and they are going to replace the cylinder head.

I'm not very familiar with engines, so can you explain exactly what this means?  Also, is there anything I should tell them to make sure the repair is done correctly? They did promise to use new parts.  Thanks!

Answer
The cylinder head is the top portion of the engine.  The cylinder block would be the lower portion.  The purpose of the timing belt is to keep the valves in the cylinder head in proper time with the pistons in the cylinder block.  Without going into the all the mechanical theories behind the four stroke internal combustion engine (which yours is and most current car engines are), I'll just say that the purpose of the valves is to open allow air into the engine and exhaust out of the engine, and to close to seal the cylinder to allow compression and forced expansion at the time of ignition of the fuel.  If the timing belt isn't installed properly, allowing a valve to be open when the piston comes up, the piston will strike the valve and bend or break it.  Depending on exactly what occurs, this can damage the cylinder head as well.

From what you've described, it sounds like the shop is attempting to fix this properly.  They're using new parts and they've freely admitted the cylinder head is damaged.  They could have not mentioned the cylinder head and just simply attempted to install new valves.  As far as making sure, there's little you can do.  As someone with limited knowledge of engines, it'll be nearly impossible for you to tell whether they're doing things correctly or incorrectly.  

I will say that this isn't the type of work I recommend for brake/exhaust shops, since it has little to do with either.  Replacing the timing belt (and cylinder head) both require a certain amount of expertise and knowledge about the mechanical workings of the engine itself, and you stand a much lower chance of finding this expertise in a muffler/brake shop.  In the future, you may want to save this type work for a general repair facility (with an excellent reputation) or the dealer.