I started hearing the timing chain death rattle, and repair history showed no evidence of tensioner replacement, so I dug in. At first I was happy to see that the upper tensioners were the newer metal ones, but one had failed leaving a very loose exhaust cam chain.
It took some work, but I finally got down to the lower chains. The tensioners were the original red/orange plastic, but surprisingly they were still intact with no cracks. BUT the guides were trashed! The chains were still in good shape, but replacing them anyway.

 

One of the metal tensioners failed? Was the plastic missing, or did it not press against the chain?

 

Plastic was there, but no pressure against the chain.
Picture may not show it clearly, but I could lift the chain from the tensioner almost 1/4 inch

 

I've been very curious about this. We know the plastic tensioners are not good. We know metal one's are the way to go, however, I have never seen anyone comment on the life span on the metal one's (05 here) and what are our guides made of?

 

The guides are plastic to prevent chain wear. There were a couple of metal tensioner failures reported previously. I read somewhere that they have a ratcheting cam that locks in place, so I don't understand the mechanism of failure.

 

I've done so much to keep this car from exploding I now worry us metal tensioner guys may need to replace even those at some point, and those plastic guides are going to give me bad dreams as well.

 

RJ, I believe that the primary tennsioners are the ratcheting type.

 

Okay, so what keeps the secondaries against the chain? I know when I pull the pin they pop up and stay there.

 

Would a 2002 XKR have the plastic variety?

 

It could. The engine serial number includes the date of manufacture. I can't find my note, but I believe aug 13 2001 is the changeover . But to be certain, remove the right cam cover and inspect.

 

I was replacing cam cover gaskets on a xjr today and observed that there is quite a lot of slack in the right side chain, but no noise on startup. Tensioners are metal.

 

I looked at my secondary ones recently. At first when I opened the cover they were tight as they should be. A few days later I noticed they were a little loose. I believe the oil pressure keeps them tight and then the pressure bleeds off and they appear slightly loose. Just my take on it.

 

only goes to reinforce what I've been saying all along about those who say the only real issue is the secondaries. For a few quid more, do the whole job, if one part is failing, the the rest will soon follow suit. Also plan in a sump removal soon after for 2 reasons, 1 is that there is every chance that bits of the guides will be in there and 2, when you do the work there is every chance that something will find its way into the sump no matter how meticulous you are

 

[QUOTE=taxman;1791362] BUT the guides were trashed!

Hi taxman - thanks for sharing - same issue with the guides was on my XKR,
and I replaced the chains as well as recommended.

 

I'm doing the lower tensioners on my other thread but I DO NOT BELIEVE these are supposed to be super tight. They should have some play indeed because they are spring loaded.

 

My appoligies for not answering your question sooner RJ.

This page is from the Engine Repair Course Code 168.
The Secondary Tensioners use oil pressure.

Now this my idea on how they work and nothing I have seen written.
There is a spring inside the secondary tensioners. The pin you mentioned keeps the spring compressed for ease of installation and once the tensioner is installed the pin is removed and spring expands tightening the chain. I'm guessing the oil pressure while the engine is running keeps excess slack out of the chain.

The primary tensioner I have only changed once. I know it has a ratcheting mechanism because I had to remove them when I had to change the guides, the ones in the kit I purchased were the wrong ones. I had to reset the tensioners, release the ratcheting mechanism. I don't remember off hand how I did that but it was with the help of Motorcarman.

 

Are you sure the metal body secondaries aren't also supported by a ratchet? I haven't had one in my hands for a couple of years so I can't check. I'm in the process of buying a '06 but I'm not going to pull a cam cover just to find out.

 

Good day RJ,
Finally had the chance to check with a new metal body secondary tensioner I have at my shop.

I gently contracted the tensioner and pulled the pin. I then released the tensioner. I was then able to compress the tensioner in my hand and reinstall the pin. There wasn't any ratcheting. It feels like there is a spring inside but it is a fairly weak spring. I'm not going to break it open to find out.

 

RJ, I concur with BobRoy. My new secondaries were spring-loaded with no ratchet. With the pin out (prior to install) I could compress the spring in/out. The new metal main tensioners did have a ratchet mechanism (spring loaded) and had a port for oil pressure.

 

Thanks guys. Someone posted the misinformation a couple of years ago. He was looking at a primary and didn't know there was a difference.

A member recently started a thread claiming that a metal body tensioner had failed because the chain was slack and it rattled on startup. I suppose the internal spring may have failed, but is that spring really stiff enough to keep the chain tight until oil pressure builds?