Thanks to all the forum members that have stressed the importance of checking the secondary chain tensoniers. Finaly got the cam covers off today to find the timebomb that coul have destroyed my jag love affair. 77000 miles ran great, not any noise and both tensoniers were cracked and ready to give up the ghost.
If you have a 4.0 xk8 bite the bullet and examine yours.

 

Two weeks ago with 60,000 miles on my 2001 XKR, I had the plastic tensioners replaced. My car had the second generation plastic ones and they were both cracked. I now sleep better at night!

 

Good to hear you caught them in time.

I've added chain tensioners to your thread title so it comes up associated with disaster in forum and internet searches.

Amazingly there's still people out there who ignore this ticking time bomb.

Graham

 

Me too. Had mine replaced at 50K just for insurance. Didn't need them. I still feel better. Guess prior owner did change oil on a regular basis.

 

Changing oil has nothing to do with it. Changed mine at 54000 and they were both cracked.

 

Just bought ANOTHER project 97 XK8 on a whim, owner said bent valve according to his mechanic. new tensioner and chain, and the CORRECT CPS and she is running like a champ!

Always be CERTAIN you have 3rd gen, I believe the ones that failed on this motor were 3nd gen.

It will take a few more months of buffing and correcting of botched repairs to get it "right", but it was a bargain!

 

Changed my tensioners at 86000 miles, they looked to be in good conditions, but changed them anyway, just in case. $90.00 on E-bay, Indie changed them for $400.00

feeling much better now !

 

In case anyone doubts this problem, last year (2015) I lost the engine in my 1997 XK8 to this problem. It was idling beautifully, I shut it off to finish a conversation, and it never ran again. When I restarted the engine, the chain jumped, a backfire burst my intake manifold plenum, and an open valve punched a hole through piston #1. Engine had 59,000 on it after being replaced at a dealership under warranty in 2004 (at 65,000 and odo was up to 124,000). I imagined a 2004 factory remanufacture "ought to" have upgraded tensioners and the low miles on engine was a second reason I thought tensioner inspection wasn't urgent.

 

the repair is well worth the cost for peace of mind.

 

Glad that disaster was averted. Before I read this lucky scenario, I decided to bite the bullet myself and get the repair done before I drive around in the springtime weather. I'm getting an estimate from my favorite Indie dealer today for my 97 XK8. He's currently researching parts. i'm on the forum researching parts also. He recommends also just swapping out the timing chains while they're in there.

 

Mark, thanks for this.
Mine had just had a Jag. remanufactured replacement engine fitted in 2004 (actually twice but that's another story). One reason why I bought it and I don't believe the tensioner farce had unfolded back then.

I've been playing dumb and dithering over lifting a cam cover to take a look as I thought like you 'nah... surely Jaguar wouldn't do that'

I won't be delaying any longer. Timely as I've a week's holiday coming up.

Mike

 

My major concern was the secondary tensioners . the engine killers. My chains seemed ok. You do not have to remove the front of the engine to do them. I spent the money I did not spend doing the front of the motor doing all the hoses in the valley and the dreaded octopus hose. I also had a leak at the aluminum thermostat tower. Seems the po changed the tower and reused the o-ring seal with silicone added.
Down to just needing to replace the two hoses that feed the throttle body with coolant. As soon as I find the correct part numbers for them.

 

I'm a believer...my first action after buying my 98 XK8 (40K mi) was replacing the entire tensioner system, water pump and thermostat housing...a lotta dough but the peace of mind was worth it.
I am curious as to why the plastic tensioners and chain guides fail. They seem to go in the 40-60k mile range or 5 years of normal driving. They don't seem to wear out, but they crack and then come apart. However, many tensioners last indefinitely. Some say it's not related to the condition of the motor oil, I tend to disagree, in part, since the only common environment they operate in is the motor oil. What causes the plastic to degrade and crack?
Heat? Torque from the timing chain? Thoughts?

 

On my second XK I had the tensioner done right after I bought the car with 44000 miles. They were the version 2 and looked brand new. However, I don't regret the $1200.00 I paid as I know for sure now the engine won't fail for the most common reason...I hope I didn't just jinx myself.

 

The plastic-bodied tensioners crack and eventually fail because the plastic can go through cooling and heating cycles only a finite number of times.

When the AJ-V8 was designed, the engineers wanted it to be compact, thus the single-row timing chain, and as light as possible, so many composite materials were used.

If you remove the cam covers and find something other than the metal-bodied tensioners, which are the third generation, they should be replaced sooner rather than later. The supercharged 4.0 litre units did not suffer from this condition as they used the metal-bodied secondary tensioners from the beginning.

 

Not true. The 4.0 XKRs like mine, switched over to the Metal Tensioners at the same time as the N/A Cars.

 

Interesting, that has not been my experience with the AJ27S.

 

My car (with a AJ27 Engine) had the Plastic Bodied Tensioners which I replaced myself.

 

The ones I have experience with had the later tensioners fitted.

Great that you were able to avoid any further engine drama.

 

I'm sure you meant to type 4.2 litre units.