There have now been a number of posts regarding problems with the timing chain skipping or breaking. I believe some of these could have been prevented by changing the timing chain tensioner before the damage was done. The part was revised, probably around 2009 or 2010, and is different than the one originally installed on earlier vehicles. The revised part number is 12608580. This is part you want to get, most dealers should have stock.
In my case, the old tensioner simply wasnt extending as it should, it only "popped" into the proper extended state as I was removing it to replace with the newer version. Note that if the tensioner isnt working properly for a longer period of time, it can wear out the chain and the nylon chain guides, which means a bigger job that requires removing the valve cover and timing chain cover from the engine to replace the worn parts. Mechanics may recommend this full procedure in any case. If it is not corrected eventually the chain may skip, break, or the nylon chain guides can shatter. That can result in irreparable engine damage.
One symptom of this issue is excessive noise on cold starts. It sounds like a rattling noise coming from the passenger side of the engine, where the hump of the timing chain housing can be seen.
I have uploaded a video of what mine sounded like:
Even if this noise is not present, it may be a good idea to change the tensioner to the newer version, as it is said to be more reliable, and the cost is commonly around $50.
As you will see, changing the tensioner is a simple job, just unscrew the old one, and screw in the new one. Most shop manuals will say you have to open the valve cover and hit the back side of the chain to activate the replacement tensioner. This is only true for the older version, as it is a ratcheting spring design. The newer version seems to only work by oil pressure and does not require this step.
These are pics of the old and worn vs shiny new parts. The old plunger is spring activated and should be the length shown when removed. The new part has a plunger that moves slowly and freely without spring tension. You can see the oil port in the tensioner head that supplies oil pressure to push the plunger out.
I recommend doing this on a cold engine, its close to the exhaust manifold, wouldnt want you getting burned.
The size of socket you need for the tensioner is actually the same as the oil filter socket, 32mm. However, as the old tensioner is slightly recessed into the engine, my oil filter socket wouldnt fit as the socket wall was too thick to get a good grip. I had to borrow a different 32mm socket that had a thinner wall. The revised tensioner has a slightly thicker bolt head, so should be easier to get a hold of.
Heres a pic of what the old tensioner looks like installed, just a large bolt head on the rear passenger side of the engine. You can get a ratchet on it by locating the timing chain hump and following it down to just above the water pump cover.
When you unscrew it there may be a few drops of oil so have a rag handy. Also be very careful as the plunger on the end of the tensioner may not be secure and could actually slide out inside the engine if it makes contact and drags coming out.
Again, just remove and replace with the new one. Torque to 55 lb ft. Might be a good idea to start the engine and run for a bit, then turn it off and restart. This should give a supply of oil to the tensioner before putting a load on the engine while driving.
Thats it, not a big job at all. If there is still significant noise, or you know more damage was done, then the larger job of replacing chain, sprockets and guides may be needed. That is still better than losing the engine though, but be sure to get a firm diagnosis first.
Feel free to post any suggestions or feedback, I will edit this post if needed.
EDIT: thanks to moderators for fixing up the youtube link
IMPORTANT ADDITIONAL INFO BELOW!
Just a heads up, a member has pointed out that his newer model tensioner did in fact have a pressure spring that released by tapping. It looks like the safe procedure is to remove the valve cover and tap to trigger the spring release. It may happen under normal use, mine is still performing well.