I have a 2000 XK8 with around 72k miles on it. Lately, on cold start, I get a split-second valve rattle, then a slight single valve "tapping" noise that goes for about 10-15 seconds. After that, it runs and sounds fine. My mechanic says the start-up rattle is lack of oil getting to the top of the engine for the first second or two, and there's little to be done. As to the slight valve tap for about 10-15 seconds, he kind of wrote it off to the same reason. All we've done so far is add some BG oil conditioner to the last oil change. He says it helps by coating the engine components to make up for lack of oil at the top of the engine on cold start. Once I'm up and driving, the engine starts perfectly and whisper smooth on warm restarts. Is there anything to be done about the noise during cold starts? What about that slight valve tap for the first 10-15 seconds. Can the valves be adjusted? Does it have anything to do with the timing chain and tensioners? My engine is the 4.0 Ltr. naturally aspirated v-8, with the plastic tensioners, which I' m told can cause issues, and fail prematurely. Any advise? Thanks.

 

Clatter on start up can be caused by the oil draining down out of the top of the engine like your mechanic said. A good quality oil filter should have an anti drain back valve in them, basically a check valve to help with this. Cheap filters have been reported to have this problem where that valve fails or does not exist.

The 10 sec of valve slap as you call it is not really. The valve adjustment is purely mechanical by way of shims, no oil pressure is involved and if it is quiet when warm then they are fine. The noise is just the tail end of the tensioners and other things coming up to proper pressure.

You mention that you know the car has the plastic tensioners. These can make noise but they also are known to catastrophically let go without any previous noise or warning. Age is as much an issue as mileage so it would be wise to change these for the newer design as soon as possible.

 

Thanks!

 

Thanks, Charlie. Honestly, I'm "assuming" the original plastic tensioners are still installed. The previous owner didn't exactly stress himself when it came to preventative maintenance, records are sketchy at best, and while not horrible, I've had a fair amount of "just to be safe" maintenance items performed on my 2000 xk8 since purchase.
I'm also getting set to have some suspension work done as well. On bumpy roads, the rear end almost feels like it "bangs" down into holes, as if the shocks are shot. Also, I wonder if the shock/strut mounts have deteriorated to the point where it's actually come loose. According to my mechanic, my upper and lower control arm ball joints and bushings are shot as well, which makes the handling and steering feel less precise. Actually, I'm getting a little shaking in the steering, which could indicate a loose front end.
Jaguar replacement control arms (with bushings and ball joints installed) are insanely expensive, practically more than the car is worth! My mechanic is reluctant to try and replace the ball joints in the UC arms, as he says it presents the risk of ruining the control arm because of the pressure it takes to pop out the old ball joint and put the new one in. Any ideas as to acceptable after-market control arms ,sway bars, etc...that would work, and not cost a fortune? I will be replacing the shocks with new Bilsteins, as I'm told they're the best shock made for the xk8. Thanks.

 

The ball joint in the upper control arm is bolted in on a taper. There is a jaguar special tool to extract it while on the car but even without that tool the mounting is similar to lots of other cars. If he can get the control arm off of the car then using a press to remove the joint should not pose much risk to the control arm.

 

You need to find a different mechanic. That rattle on startup is an indication that the secondary tensioners are close to total failure, often resulting in valves meeting pistons.

As to the suspension, the upper shock mounts probably need replacing, both front and back. I have seen rears so bad that the shocks were floating at the top. Hold off on the ball joints until you replace the shock mounts, upper bushings and sway bar mounts. The ball joints may not be that bad.

 

You mean the upper bushings on the control arms?

 

Nope, he means the upper shock mounts, where springs/shock connect to chassis.

Former forum guru Rev Sam has a great DIY Youtube video describing this. Link below


This is a known problem on this Jag, esp. if you have bad roads. Common solution is to change the OEM “foam” with modern poly material. Not too expensive, but a major PITA DIY job.

As for your 10-15 Sec engine tap upon start up, I strongly suggest you check out the secondary tensioners esp. As you suspect there’s no service history, the problem is whether the modern metal bodied tensioner units have been installed. If they’re the source of the noise, it’s a potential engine killer! Easy DIY to have a look!



view with cam cover off on AJ-27 NA engine



View of metal bodied tensioner sitting under the chain

If you can’t DIY this, any professional garage should easily be able to check.

 

Given the age of the vehicle, the primary and secondary timing chains, guides and tensioners should be replaced as the primary chain guides often crack with pieces ending up in the sump. Do not simply replace the secondary tensioners if you plan on keeping the vehicle.

The lower ball joints can be pressed out and new ones pressed in. The upper ball joints are part of the control arms, which should be replaced since the inner bushes are most likely also worn.

+1 on replacing the upper strut mounts to correct ride height and handling.

 

I also had a bit of a rattle from the engine on start up and hard acceleration. The timing chains and tensioners were done by the previous owner so I
knew it wasn't that. It turned out to be the accessory belt pulley. My mechanic replaced it and I haven't heard it since. Maybe something to look at if
it turns out that the tensioners were done.

 

I just did my entire front end. No more rattles from the suspension. The only shake is from the wheels and tires which haven't been addressed yet. The upper ball joints can be replaced. I just had to get creative for a pressing tool/fixture to get them out and back in. That was cake compared to the rest of the job.
The lower ball joint is ok to get out but you need to get creative again to get them back in. I bought a strut compressor and made proper fixtures to take care of that, then it was very easy. Lower strut bushings were a slight challenge to change but it got it done. That is likely were most of the clunking was coming from.
Lower CA bushings were a real job, but it is also done. Love drive this car more now. TM

 

Checking tensioners - RHS Cam cover removal EP1 Jaguar XK8 / XKR (X100)