Replacing the timing chain on my 1999 Cougar 2.5L V6

I count it as a blessing that the engine didn't fail. It was close, and it could have had the timing chain fail at any time. It wasn't making noise (aside from the rattle at start-up), so I figured it was okay to drive the car to the airport and back before changing the timing set. My wife advised against it, but I figured it would be ok. She was right, but thankfully not so right that the car didn't make it.

Since I found the timing chain guide fragments in the oil pan, it was only logical to replace the entire timing set.

1999 Cougar 2.5L V6 DOHC, showing both timing chains

After removing the cover, I rotated the engine counter-clockwise and it made the left side timing chain very loose. The tensioner didn't keep tension on it in this situation. Here, I can lift the chain off the guide and shake it. The left side (front of car side) timing chain had actually skipped a couple teeth. This explains the loss of power. Getting blocked by trucks passing from behind you when you're trying to merge into traffic gets old really fast.

Check out how worn the old guide is compared to the new one. This was all because it was missing the plastic piece. Without that plastic piece, the chain just tore into the aluminum.

Old and new timing chain guide, without the plastic piece attached

Old timing chain guide that lost the plastic piece

Since the chain was so loose, it somehow rubbed on the oil pump. It looks fine still, so I'm not going to replace it this time. (The oil pump is on the bottom half of the picture, with the crankshaft protruding out from the center of it.)

Oil pump housing damage

After doing this job, I can tell you that if the oil pump ever needs to be replaced on this car, it'll be more than the oil pump needing replacing. There's no oil pressure gauge. That means that if the oil pressure light comes on steady while driving, it would probably mean "you need a new car". But it may also be repairable. You could start by taking out the radio, then you have a big pile of used parts that you roll out of the driveway. Drive another assembly of parts (commonly called a car) into the same space, re-install the stereo, and you're good to go.

Not only had one guide completely failed, the remaining three guides all had fragments broken off. They were barely hanging on.

Broken chain guide, barely hanging on

So, to prevent the plastic from coming off the new guides, I glued the plastic pieces on all four new guides with black RTV silicone. I wonder why the engineers didn't implement something like that in the first place.

Glueing the timing chain guides together

I find it puzzling that they warn us to never rotate the engine counter-clockwise, but this can happen a little bit every time you shut off the engine. Also, what happens when you stall the engine when you're trying to start on a steep incline? These things happen, and the manufacturer can't just assume that the engine won't ever rotate backwards during every-day use.

The plastic timing chain guides had a small clip to keep them from sliding off, but they look like a backwards rotation could easily dislodge them and break pieces off as I saw on my engine.

After installing the left side chain, and counting and re-counting links to be absolutely sure it was timed correctly, I noticed that the other chain had black links for aligning with the timing marks. Oh, how easier the first chain would have been if I had seen those. Oh well. The left side chain is either on backwards, or doesn't have marked links.

I got confused on how they counted the links. The literature says that there are ten links between the timing marks on the intake and exhaust cams. I took that a little too literally. There are ten whole links if you put the marked link over the mark, instead of putting the mark between the links. If you line the marks up between the links then it's 11 links between the two cams, and 24 instead of 23 from the cam to crank mark.

If someone ever takes this engine apart, they may wonder how in the world the chain skipped a tooth on all three sprockets, yet remained exactly in time.

So if you have a marked chain, then put the marked links directly over the timing marks, and count the unmarked links between the marked links and you should end up with 10 links between cams, and 23 between cam and crank on the non-tensioned side. That goes for both chains.

One thing I learned on this job was that there's a special way to rotate the cams to neutral. At cylinder 1, TDC of the compression stroke, the left side chain's cams are in the neutral position. Remember, left side chains are on the right if you're facing them. Let me explain. No, there's too much. I'll just summarize. Left is in reference to the left side of the engine as you sit in the driver's seat in a traditional rear-wheel drive vehicle.

If you then rotate the crank clockwise from TDC so that the crankshaft key is in the 3 o'clock position, then the right side cams (your left . . . towards the rear of the car) are in the neutral position. If you try to install the second chain with cylinder 1 at TDC, you may have the cams snap-turn and pinch your thumb. It's okay. My thumb is fine now. Oh, and 3 o'clock is as you're facing the front of the engine. The front of the engine is on the passenger side of the car, in this case.

The car is running better now. Before the repair, it would lose power above about 5200 RPM. I mentioned that to my son after he borrowed the car, and he said "yeah, I noticed."

Of course.

Now it pulls all the way up to 6500 RPMs. I didn't go all the way up to the rev limiter, and it definitely accelerates faster than before.

Update 22 May 2017

The left timing chain tensioner failed. The product was Engine Tech brand and only had a 12 month 12,000 mile warranty. It's been almost two years since I installed it. Here's the link to that blog entry.