I am planning on replacing my timing chain guides and tensioner soon on my 1997 XK8 4.0 with 48,000 miles.

Are the factory timing chains prone to excessive wear or stretching as long as the existing guides haven't completely failed? With only 48,000 miles on the clock would it be advisable to simply replace the guides or would it pay to replace the chains also? Is it advisable to change the hydraulic tensioners at this time?

Do the JTIS files in the "HOW TO" section provide detailed procedures and torque values for this service? I purchased a (thankfully cheap) disk on eBay that claimed to be a service manual but it's basically a bunch of exploded diagrams with minimal documentation.

Thanks!

 

You will probably get a selection of different opinions on this but I hope the following is a fair summary ………

The top "secondary" tensioners (which tension the short chain between the two camshafts) are the ones which have proven to be a major achilles heel on this engine. If they fail, it is sudden and catastrophic. But - they can be replaced for very little money (two new tensioners, four shorter bolts, and some gaskets) and providing your engine is working OK at the moment and the timing is therefore accurate, they can be done in a few hours as a DIY job (just google "Jaguar secondary tensioners zip tie method".

But - to do the job properly, and replace all four chains and tensioners plus the guides, is a much more complex job, requires special tools, and, if the harmonic balancer (crankshaft pulley) doesn't want to cooperate, can turn into a bit of a nightmare. If you are doing it yourself, and have the tools, the time, and the facilities, it is "do-able". If you take the car to a garage (shop) for the work, it will be quite expensive. I suspect that most professional mechanics would be reluctant to "just" do the secondary tensioners, and I fully appreciate why that would be the case.

I'm sure there are instructions for the job on Gus' site . JagRepair.com - Jaguar Repair Information Resource but otherwise, its worth getting the "proper" version of JTIS which has both diagrams and descriptive instructions, including torque figures.

 

I am going to do it myself. I've already purchased the necessary tools for removing the harmonic balancer and locking the cams down. The engine is running well presently. I am doing this as preventive maintenance. I wasn't as concerned about the secondary tensioners as I was about the primary chain guides as I thought that they were the primary cause of valve timing related failures. Thanks for the heads up on the secondary tensioners, I'll change them out also.

Any thoughts on the chains themselves? Do they tend to wear out prematurely absent the failure of the guides?

Also, thanks for the link and the confirmation of the extent of the JTIS information.

 

Frankly - if you are taking the front of the engine off, I would suggest it is worthwhile to replace everything, irrespective of whether or not there's any visible wear. This link is to the UK product, but it is obviously available from the same source in the US.

https://www.sngbarratt.com/uk/#!/Eng...d-29f360e54702

 

+1
You will put a lot of time and effort into this, so I'd do the full monty and replace the chains 'while you're in there'. You don't want to do the job twice.

Do check the primary guides carefully as some kits contain the wrong ones for the earlier motors. See this thread originally started by Colquan1066, and particularly agd's experience:
https://www.jaguarforums.com/forum/x...2/#post1546944

My understanding is that those are meant to go with the later Morse primary chains.