I have noticed advice given to individuals looking to purchase an XK8/R models to make sure the "tensioners" have been replaced. This was even given for low mileage vehicles.

My 2001 has less than 40K on the clock and I have not had any issues with the cam chain as yet. What is the issue with the cam chain tensioners and why are they a problem?

What is the fix and when does it need to be repaired??

Makes no sense that they would fail before some high mileage was put on the car. For the price of the car new we should not be having these kind of issues.

 

Quick answer is that the early tensioners and chain guides were made of plastic to save weight, and the plastic cracks with heat and age.

These are interference engines, and the greatest risk is pistron/valve collision if a SECONDARY tensioner fails and allows the chain to slip more than one tooth. This can lead major engine damage. Failures on the primariy tensioners or chain guides tend to have less severe consequences. The majority of people who have this done see signs of impending failure (cracks) in the old secondary tensioners.

The advice on low mileage, well maintained cars is just to only change the secondary tensioners to the newer metal bodied versions. This can be done as DIY project for around $200, or a competent shop for a about $800.

No one is happy about it, but that is the reality on these cars.

 

My '02 with 46k miles on it in '09 had cracks in both secondary tensioners.

Change the tensioners! $200 now, $5000 later.

 

I just did my secondary tensioners on my 2000 XK8 with 40K on the clock. Both tensioners had started to crack and they looked to be the second design. There is a definite design flaw in these tensioners which I will describe in a future thread I will present as soon as I sort my pictures and figure out how to include pictures in the thread. I actually liked the basic design of the second iteration that was plastic except for the design flaw that doomed them all. The metal ones are now in my car.

How much farther would they have gone? Probably another 10K for sure. But not now.

 

WhiteXKR:

Take it from an ex-Ford employee--Jaguar didn't put metal tensioners and metal impeller water pumps to save weight. It was to save money--probably $20 per car.

Common sense tells you that plastic will not hold up over the long term, especially when being heated up and cooled down many times per day.

Warranty claims on replacing engines cost Ford/Jaguar $ millions--not including the damage to their reputation. It took 9 years of constant changes to correct the design errors to where the XK8 was somewhat dependable. It was the Battle of the Engineer vs. Accounting--and no one won.

 

I stand corrected !

 

Please don't forget

 

I've changed alot of these tensioners and here is what I see:

the catastrophic failures are caused by two things. the first and most common is when the plastic "slipper" cap cracks and comes loose from the metal plunger. if it falls away down to the oil pan, no problem xcept now you have a metal chain riding on a metal plunger. the real fun comes when the slipper ends up stuck between the chain and the gear, breaking the chain, jamming the chain against the head, locking the exh cam in place. the pistons come up and whango, there go the valves, and maybe pistons. usually on the middle cylinders. if you are fortunate the chain doesn't jam against the head and the exh cam goes to a neutral position where all the valves are closed. valvespring pressure pushes it to this position. the second failure mode is when the body of the tensioner cracks far enough that the plunger assembly falls out. I've only seen this a couple of times.

 

As this comes up again and again as new owners visit the forum I think this may help. Go to this Forum and Scroll down past where it says "Index" and the articles are there (DBL Click to enlarge them). The first two items are articles on Nikasil and Cam Chain Tensioners. I actually learned about the issues there before discovering this Forum (Which is THE BEST BTW). Based on the article I decided to replace chains and guides and I'm glad I did. Not only the secondary tensioners, my chain guides were severely cracked and would have failed eventually. I have copied these and forwarded them to several members and they all greatly appreciated it.

MODERATORS, you may want to add these to the FAQ section as they are excellent sources of info. I would suggest to copy and paste them to a Document and place that in the FAQs..permission has been given to do so.


http://www.jag-lovers.org/cjw/#0104a

 

Grabbed 'em steve, i'll get them in the FAQs hopefully soon.

 

I don't mean to be a whinnier, but if Jag knows that these cam chain tensioners are a basic defect why don't they stand behind their product and pay for the fix.

When you spend 75K for a car you would think that even when the car is out of warranty the mfg would want to insure that its reputation was intact. Not logical to me that they turn their backs on folks with low mileage cars with the potential for a blown engine.

I am surprised that some enterprising young lawyer has not picked this up as a class action lawsuit.

Not my thing to sue anyone but its almost a "common sense" solution to a major problem.