What type timing belt should I use for a 2000 XK8 and how do I tell what type is on the car now?

 

No timing belt, it's chain drive. You should use the search to read up on replacing the chains, tensioners and guides. Also search for upgrades for the ZF transmission.

 

 

Timing CHAINS and drive BELTS on the XK8.

Graham

 

Thanks. I read from previous questions that a belt (serpentine or chain) should be upgraded in order to prevent a major failure. that's the belt I m inquiring about .
I cannot find those previous questions and answers.

 

 

The engine operates the intake camshafts with 2 separate long "primary" chains off of the main crankshaft. The slack in the chains is managed by tensioners pushing on plastic guides. Over time these parts wear out and need replacement.

Exhaust camshafts are operated by short "secondary" chains. The slack in these chains is managed by 2 separate tensioners which are the problem parts. The initial version was plastic, a later redesign was done, and eventually an all-metal version was issued by Jaguar for the later 4.2L engine. This all-metal unit is what you NEED. All earlier versions eventually crack and allow the slack in the chain to go uncontrolled, possibly allowing the chain to skip teeth, leading to collisions of valves with pistons. Sometimes, the secondary chain breaks, wraps around, and basically ruins the entire head. The only way to be sure is to pull the valve covers and check what tensioners are already there. If you are lucky, a previous owner will have tackled that particular job, and you will be back to normal maintenance considerations. If not, this job needs to be done as quickly as possible, likely without starting the engine again. As these cars are not worth a ton of money, major mechanical problems like failed tensioners can swallow whatever value is left in the car, unless you can do most of the work yourself, and the damage is not too extensive.

Best is to search "secondary tensioners" on this forum or others. The Jaguar engine type is generally "AJV8", with the AJ26" and "AJ27" 4.0 variants.
Another search is for the "zip-tie method" that a member detailed a while back.

Best of luck, keep us posted.

 

It's the early PLASTIC tensioners on the timing CHAINS that fail causing catastrophic damage as valves and pistons come together. Search "tensioners" and you will find enough posts to keep reading for a week!

Graham

 

 

They designed the engine so that the piston and valves could contact each other? Brilliant! I guess they couldn't find a couple centimeters anywhere. Well I'm glad I will be replacing the timing chains and tensioners in my car in a couple weeks.

 

It's hardly a unique feature, probably more interference engines out there than not.

 

Stu,
"...a couple of centimeters ...." means a lot to engine designers. Size is important and reducing the size of the engine allows a lot more than just power-weight performance. The AJV8 block is aluminium as well to save weight.

The debate between interference and safe engine designs rages on. People tend to forget that the engine block is a service part. Classic American muscle cars often have engine rebuild kits. Not so much British cars.

Consider this, safe engines have to be bigger and thus are more expensive to build. Typically safe engine designers try saving money by using only rubber belts, whereas the AJV8 engine uses the serpentine rubber belt for secondary ancillaries only, and uses steel timing chains for the critical camshaft timing. The concept was sound, albeit the chain tensioners were poorly designed at the beginning. The use of Nikasil bore liners was also a sound concept but the lining was prone to sulphur attack and led to reputational damage to the Jaguar brand. Also note that the ZF5HP24 transmission was especially made for the XK8 grand tourer.

The car was ahead of its time, but in hindsight maybe they tried too hard with new stuff.

 

it's just a compromise engineering solution. If an engine is maintained properly, then an interference engine will last just as long as the non-interference type.

You can pretty much classify the interference engines as performance engines and the non-interference engines as dogs. There are exceptions of course.

WOOF WOOF


Z

 

I am surprised that the engineers would design an interference engine with cheap plastic timing chain tensioners.
It's like they intentionally designed a weak point into the engine.
Sure, they may have saved a few grams of weight, but at a high cost.

 

 

Especially today with the price of cars, I expect them to last much longer than 10 years, and they do with proper care.
Most light bulbs on this car have outlasted the engine. Is that what the engineers intended? Give me cheaper bulbs and spend those dollars on the engine.
There may be a day when plastic is suitable for internal engine components, but that day has not come yet.
I was ready for an engine project so I'm not upset about changing the timing chains and tensioners,
I'm just disappointed that the engineers didn't know better.

 

The engineers knew better. Unfortunately, the accountants overruled them....

This issue was corrected in the 4.2 engines. All-metal tensioners became the norm....

 

most of these plastic tensioners last beyond the 10 year mark. On my particular car, the tensioner, etc lasted 15 years / 115,000 miles, and were replaced by the previous owner. That said, most cars have some Achilles heel that slips by the engineers and only mass testing by the consumers exposes the flaw.

Back to the engineered in obsolescence or "expiration date" idea. If cars were engineered to last, really last, from stem to stern, for say 20 years, what would that do to new car sales ? LOL. Car manufacturers would never survive that hit.

Z

 

Totally agree with Zray, that we're keeping alive the XK8 that is way past it's expiry date. That's half the fun though! Cars nowadays follow the post -war Japan's production line 13 step principles, and low cost cars nowadays can almost be considered disposable past 5 years.

As an engineer myself (civil construction), there is always the balance between cost and technical delivery. Any engineer is normally given a budget for a particular job, and then ususally he has to make compromises to fit the budget. I think there were something like 65,000 XK8s and 20,000 XKRs built. Saving a few bucks here and there would have made a difference to Jaguar's production costs.

Only enthusiastic owners like us now, continue to try and keep old cars on the road where I find getting parts, esp. the rare bits, is half the fun. Some costs though aren't much fun.

 

I understand what you guys are saying, but how can you justify burying such a weak link in a $70,000 car?
Would it have affected sales if they raised the price of the vehicle $50 to install metal chain tensioners? No. That takes care of the bean counters.
As for the engineers, shame on them. They should have known better, which they proved that they did by fixing the problem in later years.
Remember that Jaguar was in a position to overcome a long standing poor reputation for reliability. And they did this to save the cost of a steak dinner? Absurd.
I maintain my position that there was no legitimate excuse for this oversight and Jaguar realized that later.