Mornin' all,

Usual background.... 2000 XJR, 160k miles, largely unknown history. It's been mine for around a year and 20k miles and was quiet as a mouse... until recently.

A couple of days ago, I noticed an engine rattle at what I shall describe as "full power". I grandma'd it home, and - when restarting to pull it into the shop - I got a short rattle at start (0.5sec max).

Thinking 'tensioners', I pulled the RHS valve cover off this morning. It's already got the 3rd-gen (metal) tensioners fitted, and peering into the abyss the chain guides are metal. There's no slack in the primary chain, and I can move the secondary maybe 0.5mm off the tensioner at most.

I'm going to pull the other valve cover to make sure a PO didn't do just one side (why would anyone do that?).. but.. my question for the forum.. what else can cause startup rattle *aside* from timing? Do the 3rd-gen tensioners ever need the top "slide" part replacing? Do the oil pumps "go"? Would a poorly-maintained supercharger cause a rattle?

Any wisdom much appreciated.

 

With your mileage I would suspect that the primary tensioners, or more likely the guides, are up for replacement.

The secondary 3rd generation chain guides are plastic. Are you referring to the primary guides? They should not be bare metal.

 

+1 what Testpoint says- you should be seeing plastic wherever the chain touches, definitely not metal.

 

Well, in the spirit of 'a picture says a thousand words'...

Here's the left side:



...and here's the right:



...and here's me trying to take a picture of the right-hand primary chain guide that I thought was metal:



...and the same pic of the left:



Some things that look weird to me:

1) In the second pic, the secondary chain is flat across the tensioner and it's being pushed "up" in the first pic. I couldn't feel any spring pressure in either side.

2) The primary chain on the left side is noticeably loose. If I reach down and flex it near the guide, I can deflect it 5-6mm. The right side primary chain is tight.

3) In the fourth pic (showing the primary chain that's loose), the guide looks.. well.. different. Is it *supposed* to look like that?

Thanks again for your responses so far. My expertise is in Rover v8s and old Triumphs, so a lot of this is new to me.

 

I can speak to the difference in the two sides. Remember, both chains are running on sprockets turning in the same direction and the intake cam is pulling the exhaust cam with the chain. So, on the left side, it pulls on the bottom and the slack side of the chain is up. On the right, pull is on the top and the slack side is down. The tensioner pulls up the slack side and is only a slipper plate for the tight side.
I am not sure I remember what the original primary guides look like (my replacements are different) but I THINK yours MIGHT be missing all of the plastic piece. You could drain the oil through a strainer and see if you find some plastic chunks!

 

Weeeeeeeeeellllllll... I found a receipt in the huge pile of stuff that came with the car that said the timing gear was replaced at 60k miles... in 2006. It lists "chains, upper/lower tensioners, all guides and gaskets".. as well as a bunch of cooling hoses.

As that was almost exactly 100k ago, it seems fair that it's due again. Either the left-hand chain is stretched, or the left-hand lower tensioner isn't tensioning.

Either way.. tomorrow is cover-off time. I've found some excellent write-ups in the forum, so - aside from waiting for tools and parts, and finding a huge breaker bar - I'm going to have at it.

 

Please let me know what you find on the lower chains.
I have a 98 xk8 with 132,000 mi that has what sounds like a loose chain only at a cold startup .
I pulled both valve covers thinking I would find the plastic upper chain tensioners and found the newer metal ones. All the chains and guides look good and tight from above to me.
I think I will try turning the engine over with the starter to see what makes the noise before I put the covers back on.
Thanks, jon SE Portland

 

I got a rattlingish sounds on full power only which was gone after I tightened up the two bolts on the EGR valve so might be worth checking that as well. EGR probably needs cleaning if has never been done anyway! Good luck with the rest

 

Going to get into this properly next week.. waiting for tools to show up. I expect to find a failed primary tensioner on the left bank, as I find it hard to believe the chain could be stretching that much without breaking or skipping...!

On the plus side, I'm back to using a Rover P6 as my daily driver.

 

I am going through this right now, my lower RH tensioner failed, causing lots of slack, but only at certain spots in the rotation due to the loading of the chain caused by the valve springs and cams.
Your lower guides look just like my original ones. The latest ones look quite different, seen here.
[IMG][/IMG]

And my original ones.
[IMG][/IMG]

Notice how the tensioner piston is bottomed out. There is a check valve inside that traps the oil to keep the chain tight when the engine is shut down. It rattles on start until the oil pressure pushes out the piston.
[IMG][/IMG]

 

Right, parts and tools on way.. this is the weekend project. Massive breaker bar on standby.

 

For anyone else who happens across this in future.. I got the crank bolt off in about ten minutes. I used a 24" chain wrench and a piece of old belt taped round the pulley itself (as mentioned in several other threads) and a 3ft breaker bar.

Now on to the pulley itself.

 

I actually shattered the center rod thing on my new Sears puller trying to take the crank pulley off.. so that'll be going back tomorrow. On the other hand, the crappy Harbor Freight puller that I bought about six years ago got the pulley off in about five minutes...!

 

...and today, it's all back together and running.

Only snags I hit on reassembly were figuring out how to torque the crank bolt up properly.. and working around the fact that a previous owner had stripped the thread on the supercharger tensioner bolt. Helicoils are useful things!

 

So you are using the old belt just to protect the pulleys from damage?

Hmm... 21st to 23rd ... you work fast

 

Yes, a 22" length of old belt taped round the pulley worked just fine. It didn't slip at all. Kudos to whoever posted that particular tip first, but it worked *really* well.

Have yet to take the car anywhere yet tho. Got a small oil leak on the r/h valve cover; I'm guessing the gasket slipped or something. Obviously it's right over the exhaust

 

I actually watched a guy next to me at the dealer use his 24" chain wrench and a piece of old belt so I stopped using the special tool (that was always missing from the tool room) and bought a Harbor Freight chain wrench.

It was faster to attach and it works fine.

I posted this but I never gave him credit. His name is Gary Green and if you see him, buy him a beer.

bob gauff