I have 112,000 miles on my 2007 XKR. Does anyone know if the timing chain should be replaced? If it breaks will it damage the engine? How much does this service cost?
John, La Quinta CA USA

 

Eventually everything wears out, the chain, the guides, etc - but not likely for another 100,000 or 200,000 miles.

I suspect CA will give you grief on emissions long before then

 

The chain is not going to break like a belt.
The car will give you plenty of warning when it gets stretched.

You will not be making a future repair more expensive by ignoring the timing chain.
You will make it cheaper and possibly free.
For instance someone hits you hard in the rear, you wont have to worry it about anymore.

These days it does not pay to do things preemptively.
Because the failure is not certain. And by the time you need one, say 200k miles, you may have other things you want to replace then, maybe even just drop in a new engine.
Also the part you are putting on (say waterpump) may not be as good as the one you took off, which you know lasted 100k miles.

 

 

No experience with XKR timing chains, but in general terms V8 engines with overhead cams are hard on chains due to complex shape and length.

In general terms here what could go wrong:

1. Chain stretches
2. Cam gears wear down
3. Chain tensiometer fails
4. Chain guides got worn and or snap

If one or more of these issues combine or you get particularly unlucky chain can jump and that causes engine damage similar to what happens when timing belt snaps.

Personally, I'd address chain issues as soon as I detect signs of trouble. Start with making sure chain tensiometer fully operational. Doing this is cheaper than a new engine or new car.

 

From my perspective, I wouldn't open the engine only to replace the timing chains.
I look at it from a performance versus reliability perspective.
I your engine has been driven hard with a heavy foot, it might be something I would consider.
There is a higher probability that a coolant line, or electrical component will suddenly fail that leads to engine damage.

What SinF wrote is something to consider.
1. Chain stretches
2. Cam gears wear down
3. Chain tensiometer fails
4. Chain guides got worn and or snap

What no one has mentioned is that as the engine ages, its performance will suffer because of the wear on the timing parts. Whenever you floor the car under full power and run up the rpm at 5000 to 6000 rpm, the risk that something will go wrong increases. If you know the car's service history, and the engine has been properly serviced during its life, then 112K isn't that high of mileage for our engines.
If the car had been neglected and/or driven hard over its life, then you might consider changing the timing set, while you are at it, the oil pump and water pump. If you can do the work yourself I guess $600 in parts, $100 to $200 in specialty tools and a lot of your time. If you pay someone, expect $2+K to get it done.

I am putting in a new timing set, oil pump and water pump into a refresh 4.2L SC engine I have. This engine only has 75K miles on it, but I felt it was a false economy to put the engine in as purchased.
Today I ran into a weird situation where one of the inlet cam timing gear bolts wouldn't tighten up to 90ft lbs. (Incrementally tightened, first at 70 ft lbs, then 80 ft lbs, then over 80, the bolt just wouldn't tighten.) Took the bolt back out and it was deforming below the head. Had to replace with bolt with another one.


Good luck.

 

Spot on Tijoe.

I should have started my post with "Assuming you want to keep your car long-term, you should address timing chain issues as they arise or you will risk much more expensive engine repairs down the line". With XKR values at the lowest point in the depreciation curve, it might not make financial sense to tackle this job. However, eventually you won't be able to buy a clean XKR at current low valuations, so "fix chain vs. just buy another XKR if my chain fails" won't be a consideration.

Personally, I err on side of fixing auto issues I am aware of, as letting something operational fail because it is cheaper to replace entire car sounds irresponsible to me. Manufacturing and recycling cars is far from environmentally friendly, keeping your car running the longest possible time is by far better than even driving a Prius.

 

Thanks to all for the info. But it leaves me uncertain as wether to wait and see or replace. I plan to keep the car long term...so I guess it is probably expensive insurance!
One more thing --do the oil pump at the same time, along with the new improved JAG water pump (metal, not plastic impellers)??

 

In the long run, we are all dead.
The timing chain will outlive many other things in the engine.
What makes you think the seals and plastic components will last longer?
I bet you need a rebuild long before the timing chain wears out.

 

From what I've seen, it's best to do what is necessary to avoid an overheating event if you want the engine to last for a long time. The AJ-V8, in all versions, becomes very unhappy when overheated.

Obtain the latest version of the water pump if it's being replaced.

 

Look for signs of chain slap if you can take a look with a probe. Listen for cold startup, some initial rattle is acceptable but if it lasts more than couple seconds further investigation is warranted. If chain stretches, it also retards valve timing that ECU will have to compensate for. You might be able to pull values to determine how much. On old non-variable timing engines that would manifest as loss of power and poor idle, but modern engines can compensate and hide this effect.

 

My 2007 XKR has 75000 miles now and I grit my teeth at startup. About 20% of the time there is clatter and I'm convinced it's at least one of the chains. Is the consensus some noise at 75k is fine? The 4.2l sc doesn't usually need a timing set refresh? Before my last oil change I put in half a quart of red atf and ran it 600 miles hoping to clean the tensioners. I don't think it helped.

cheers!

 

Yet we are led to believe that doing regular oil changes every 3k miles it can solve this

 

timing chain would be odd... supercharger a possibility?
in days gone by we did use atf fluid for such reasons. The jury is out if it was at all beneficial. There are better products available today.