I have seen many threads asking about a noise on start, and to help discussion, I have posted two videos. The first one has the best audio, in terms of hearing the tapping.

In the second one, I raise the revs to about 1500, and you can heard the sound it makes, then the absence of the tapping.

VID00008-20110923-1632.mp4 video by avt007 - Photobucket

VID00009-20110923-1634-1.mp4 video by avt007 - Photobucket

I hopes this helps someone, feel free to ask questions. This car has made this sound since I bought it for the last 20,000km or so, with 10/30. 10/40, and Restore.
Personally I think it's the VVT and I don't worry about it anymore.

 

had the upper tensioners done? If not, do so.

 

Ay, caramba! My 01 VDP (78,000 mi) just started making this noise. Only happens after a cold startup, and then only for a very few seconds. Sounds like a very noisy hydraulic valve lifter. (but probably isn't?) I listened carefully with the hood/bonnet up. The noise was not obviously coming from the front of the motor, maybe somewhere along the middle, but definitely at the top.

No, I haven't changed my secondary tensioners yet. When the tensioner goes, does the noise persist after startup?

 

Hi, did you ever discover the cause of the knocking at startup? My 1998 XJ8 has just started making exactly the same noise. Just as in your video, if I rev slightly, I get the same brief rattle and the knocking stops. the car then runs quiet as a mouse until I restart. Previous owner says the tensioners were replaced in 2011, though I haven't yet pulled the cam covers to check.

 

Use a stethoscope. Sounds like the water pump to me.
I get a slight valve tapping at start up, obviously, one of the lifters is taking some time to get oil pressure up.

I don't think the sound on these videos is the same that you get with bad tensioners.

 

I made the original post almost 2 years ago, and now at 250,000 km, it still does the same thing. Tensioners are different, the XJR I just bought sounded terrible, and today I am tearing down the front end to find what I suspect is a failed primary tensioner or guide rail.
Jim, IMHO, it's not a water pump, the behaviour has been unchanged for ten of thousands of km. Tap tap when it's cold, then ka-chunk,and it's perfect.
I am still guessing VVT. Having said that, I haven't checked the upper tensioners yet, so I may be sitting on a time bomb.

 

Not a hydraulic lifter.....these motors have solid lifters

 

Hi Guys.
Did anyone ever find out what causes this noise?
I'm getting the extact same noise!. If I rev it rattles then goes away but sometimes the tapping comes back on tickover.
I guess I should check the tensioners (it's one of the jobs on my list)

 

Hi,

My XJ8 suddenly started with this problem 4 months ago, (see my previous post), exactly as in the video. Tapping when starting up, most times but not every time. A short rev, a brief noise then quiet as a mouse. But only comes back when engine is turned off for a while then restarted. My tensioners were replaced 2 years ago but it does not sound like the tensioner problem. As has been previously suggested, could be a VVT problem. Now over 2000 miles on it remains unchanged but no other apparent ill effects. (see AVT007 posts on this problem). Still wise to check the tensioners, even though this is likely not down to them. Cheers

 

I experienced the same problem with my 98 XJ. the problem was drivers side upper tensioner it was slack after sitting and would pump up after starting. replaced it and no more noise. By the way I had previously did tensioner replacement with new ones. if you take off the valve cover you will find one tensioner with slack. Normally when you pull the pin installing them the tension will take the slack out of the chain. One of mine just collapsed fortunately no damage to engine.
Vern
98XJ8
97XK8

 

I had this problem with a 2001 XJ8 I bought earlier this year. It ended up being bent valves and stems. Valve job on Bank A cleared up the knocking but uncovered low compression in cylinders 3 and 4 on that side.

All this was due to an engine melt down when secondary tensioners failed about 3 years previously.

I will be taking a big loss on this car. Too expensive to rebuild or replace engine. I have bought a 2002 with only 49K miles that I have recently did tensioners and thermostat tower housing upgrades.

You can skip the video below to 1:06 to hear the knocking and avoid some of my uneducated commentary.


BTW, the knocking would go away completely after the engine was totally warmed up (about 6-10 minutes). I test drove the car three times and the previous owner always had the car warm. I was a fool to not notice. I asked him about it later and he said, "Oh, yeah, it always does that. But it stops after 1o minutes." Honestly, it was so loud I was embarrassed to pull up to a stop light. People around me looked to see where the knocking came from!

This car no longer makes the knocking but does go in and out of Restricted Performance sometimes due the low compression and misfire detection.

It is available for someone wanting a project. Would be happy to let it go for $ 2,500.

 

My car makes a slight clacking on cold start up (not a knock or tapping). I have a one car garage, so I can hear every little tick and tock. My secondary tensioners were replaced, by me, shortly after I got the car and were both cracked. I know my noise is the VVT pumping up. You guys are playing with fire if you don't check out those tensioners. Bent valves are not something you want to worry about.

 

My 2001 XJ8L also has a faint tapping as the VVT pumps up; nowhere near the knocking sound Robert has. Danielsand said his wife's cat also has a VVT noise at cold start. I believe it may be dirt in the sensor, but for now, leaving it alone. I will note that when I went to 5w40 Mobil1, it quieted for about a week.

 

Update, sort of. 3 years later and it makes the same sound, after trying Restore, and different oils, and after replacing upper tensioners.

I'm sure it's the VVT,and I'm equally sure I'm not going to fix it.

 

My thoughts on this thread. I have a 98 vdp, 5000k miles after my upper tensioner change out, my jag started this tapping on start up but clears after I get the oil pressure up. I understand jag used solid lifters, but the tensioners are hydrolic.