XK tensioner upgrade - 2010 5.0 engine.

Here follows my account of recently upgrading the timing chain tensioners.

0. Background:
5.0 XKs and XKR engines are almost all fitted with the INA chain with an 8mm pitch. Sometime after the first few years of production the chain adjusters were upgraded in response to their early-ish failure, there were two interim upgrades before the latest version which as far I can tell overcame the earlier ones shortcomings.

Cars with VIN up to and including B49165 had the first (not very good) blade and tensioner combination fitted: parts AJ812420 and AJ822419.
From VIN B49166 to B52040: parts AJ812972 and C2Z20682.
From VIN B52041 to B52835: parts AJ813562 and C2Z28428.
From VIN B52836 the last version was fitted, these are the recommended upgrade parts: C2Z28431 and AJ813898.

Jaguar published a procedure to upgrade the tensioners (attached) that does not require removing rocker covers.

I decided to combine fixing the leaking front crankshaft seal with a visual inspection of the tensioners and the upgrade if appropriate; it was.

I found information (a lot is Landrover) but couldn't find an account from someone who had changed just the tensioners specifically on an XK. So here's one to help other DIY mechanics, or maybe guide them towards sending it off to a specialist.

My decision to go ahead was based on there being no outward signs of chain slack, a modest mileage of 83000, history of regular yearly servicing. On inspection I found all the timing components looking good except for an indentation worn about a millimetre deep into the back of each tensioner blade by the plunger. The tensioners were the earliest type.
The tensioners had not adjusted much and were still effective, the chain had not stretched and sprockets were in good condition. I therefore decided on changing just the tensioners and guide blades to the latest versions.
(If the chains were stretched and sprockets worn it would be worth removing the rocker covers for a complete renewal)

The special tool I needed was the crankshaft pulley and bolt removal kit which was about £100 on ebay. I already had a 200Nm torque wrench, ¾ drive ratchet wrench and a length of suitable pipe to achieve 600Nm torque. In order to hold the crankshaft when undoing screws on the pulley Jaguar specify a tool that bolts in place of the starter motor and locks the starter ring; alternatively, I used a flat steel bar with holes drilled to hold the pulley by two of its screw heads.

Crankshaft pulley holder from 8 x 40 steel bar.

Parts bought were two new tensioners plus guide blades, front seal and new crankshaft pulley bolt for a bit over £400 including tax. I bought the corresponding Landrover parts from John Craddock: LR095472, LR051013, LR010706 and LR011952.

Guided by the workshop manual, the attached Jaguar procedure and a recollection of internet stuff, this is how I proceeded :

Reference to Left or Right means the side as viewed from the driving seat.

1, Preparation -
Unlock, open boot and trip the latch so it won't relatch accidentally, now disconnect the battery negative lead.
Jack up the front and secure with stands to give good working space beneath, about 8 inches space under the wheels was enough for me.
Open the bonnet, detach the struts and insert 8mm bolts to hold the bonnet in the service position. Use something to cover and protect the wings.

Towel and leather from an old sofa.


A lot of stuff needs removing to get decent access to the front of the engine..
Have your phone handy to record where things were before dismantling. Label hoses and connectors, bag up fasteners and keep with whatever they held on. Store everything carefully so not to miss anything on reassembly - it might not be for a few weeks if a delivery is delayed or other priorities crop up.

2, Covers and undertrays:
Unclip the engine cover, plastic cover and flexible injector cover on Right side and the radiator shroud. Underneath, remove the undertray, the front (semicircular) piece in front of the wheels and tray beneath the radiator.

3, Inlet tract:
Remove the two pipes and T junction to the throttle (T piece can stay attached to the small pipe and moved out the way).

4, Cooling:
Drain into a clean 10 litre bucket to reuse or measure it to ensure the same amount goes back in later.
Remove thermostat and pipes in front of the engine. This was hard as space is tight, the spring clips are hard to get to and rubber pipes stick. I used angled water pump pliers to release clips. A brake bleeding vacuum pump is handy to remove coolant left in pipes that otherwise ends up on the floor.

5, radiator fan:
Remove the steel tubular X brace. Unclip the wiring loom from the aluminium cross brace disconnecting the crash sensors and a temperature sensor and move the loom out of way. Detach brackets for headlights, steering fluid reservoir and radiator from the cross brace and remove it. My fan unit is fastened by just one small screw and then slides up and out after disconnecting.


6, Radiator:
The top hose can be easily unclipped now. The bottom hose stayed but I taped the open end in case I dropped something in. The attached condenser and steering fluid cooler have enough slack pipe for the assembly to be carefully lifted out of two lower mounting sockets and manoeuvred forwards and downwards. Tie it in place to provide as much space as possible in front of the subframe crossmember. You should be able to poke your head and shoulder up from below to get a good look at the engine front. I wrapped card around the radiator for protection.

You can just about get a head, shoulder and arm up between the radiator and subframe!!


7. Front pulley:
Drain about 4 litres of oil into a clean receptacle (if it's going back in). In case of memory loss, I leave a note saying “oil and coolant… “ on the driving seat.
Slacken the three screws fastening the steering pump pulley, remove the serpentine belt, steering pump pulley, idler pulleys and tensioner.
I cleaned the front of the engine again before the next step.
Two of the torx screws on the crankshaft pulley need undoing to attach the crankshaft bolt removal tool. I used a home made pulley holder to stop the pulley rotating (later I use the same to rotate the engine).
Check your crankshaft bolt has “12.9” on its head meaning it's clockwise to undo.

Crankshaft bolt removal tool. The free end is supported in the forked end of steel bar.

Fasten the special tool to the pulley with its free end supported securely. I believe the downwards force will approach 300kg. My tool came with a ¾ drive socket and I used a six foot tube over the handle to undo it. Once the bolt is out, the puller bolts onto the pulley with four bolts so you need to remove two more torx screws without rotating the pulley clockwise. The puller is straight forward to use.

8. Timing covers:
Make sure all their edges are clean so debris doesn't drop inside when taking them off. Remove the brake vacuum pump then the lower timing cover.

Original Right tensioner. The tensioner has not moved far so I'm confident the chain has lots of life still. The plunger has worn a mm or two into the rear of the blade.

The tensioners are now visible, you can get a fair idea of condition and decide whether just tensioners need upgrading or also chains and sprockets.
Remove the crankshaft friction washer.
Before removing the upper covers I positioned a rag to stop any dropped screws ending up in the sump, then removed the sensors and solenoids. As well as five torx screws holding the upper Left cover on there's a not so obvious sixth screw attaching the cooling pipe. The three fasteners at the front of the rocker cover must also be totally removed. There are two locating dowels and prizing points for levering.
On the Right side, the central rocker cover fastener also holds the fuel pipes and cannot be removed without first undoing the fuel pipe unions and clamps to lift the pipe bracket off.

Right upper cover removed. Note position of two dowels.

9, changing the tensioners:
I replaced the crankshaft pulley (using the puller/pusher tool) so I could rotate the engine to the position shown in the Jaguar procedure for changing the Left side tensioner (rearmost chain). Presumably this is a position where the camshafts are not inclined to turn. After removing the pulley. I use a carb or brake cleaner aerosol to clean then paint alignment marks on all six sprockets and chain to check the chain doesn't jump a tooth. I tied the chains to the crankshaft sprocket and tie wrapped to camshaft sprockets as shown in the Jaguar procedure.

Left tensioner first, this chain is behind the Right one. I found I couldn't extract the Left guide blade because the Right fixed guide and lubricating jet is in the way. I'm not sure if I done something wrong or the Jaguar procedure is wrong but I couldn't find a way to wiggle the Left tensioner blade out. I therefore removed the Right tensioner and fixed guide (after securing the chain and tie-wrapping the cam sprockets in place) to allow changing the Left ones. The Right tensioner blade changes without a problem.

A note about the tensioner: this is fitted with a release pin to pull out once fitted, you then check it operates by trying to depress the tensioner blade and it should only move a small amount before stopping against an internal ratchet mechanism. If you can depress the plunger all the way in then the mechanism hasn't deployed. You will need to take the tensioner off and reset it by allowing it to extend fully, then compressing it enough to reinsert the pin and then push the plunger a bit further into its body to reset the ratchet. Water pump pliers are ideal for compressing the plunger. Refit and deploy it again.
I said earlier that I couldn't follow the Jaguar procedure, the crankshaft wasn't repositioned prior to changing the Right tensioner. Probably as a result, I found the Right exhaust cam sprocket had retarded by slipping the chain one tooth. I can tell you it's not easy moving the chain back and much better to avoid that happening.
If I were to do the job again I would take more care to ensure the chain can't jump (maybe wedge small wooden chocks between the chain and rocker cover). I'd also love to know why I couldn't extract the Left guide easily.

10. Reassembly:
Reverse the disassembly order: the following notes concern bits I found tricky.
Obviously joint faces need cleaning. O rings and seals lubricated.
Jaguar say to renew the lower timing cover. If reusing, consider using a gasket sealant. The seal must be centralised whilst fitting the pulley so fit the cover loosely until the pulley is in place.
I wouldn't reuse the crankshaft bolt. I compared old and new ones, the permanent stretch was already about half a thread pitch: it's not worth risking it breaking on a second use. I read a recall notice concerning these bolts failing and causing catastrophic failure as the crankshaft end breaks.

Fitting upper timing covers needs care to make sure the rocker cover seals are not displaced, the locating dowels make it a bit tricky. Greasing the seal and a gently persuasive thump upwards with a hide or rubber hammer puts them in place.

The seal under the rocker cover is easily pushed out of place and into the engine when sliding the timing cover on. You can see it's ok here, all covered on oil.

A thin smear of silicone grease helps reassemble coolant pipes and thermostat. Refilling, the bleeding vacuum pump gets most of the air locks out, first attached to the small pipe going from the top of the engine to the reservoir and then attached airtight to the filler. Most, or all the removed coolant should fit back, recheck the level after running it though.

11. Conclusion:
The end result: the car sounds and drives exactly as before, which is absolutely fine. But, I shan't be worried about timing chains.

12. Comparing old and new:
I laid the old and new tensioner/guide sets out on a piece of card to compare.
The early tensioner plunger pushes the guide at an angle to its pivot that means the plunger must slide along the tensioner as it moves in and out. As the plunger wears itself into a hole it's movement will become impeded and eventually it will become stuck and no longer push the guide. When this occurs the chain will start to slap around.

Plunger movement is approx 60 degrees to the blade pivot. The contact area will slide 50% of the movement distance.

[img alt="Wear from the plunger is elongated by about 0.5mm. Due to the 60 degree angle with the pivot point the plunger must slide. As the hole wears deeper I think the plunger movement will become impeded.
The tensioners must be able move continuously to allow the relatively different rates of thermal expansion between the aluminium engine and steel timing components. "]https://cimg5.ibsrv.net/gimg/www.jaguarforums.com-vbulletin/1500x2000/img20250323110120_debfda4ec9195afde2a3b7c8bad8716c 56e79d3d.jpg[/img]
Wear from the plunger is elongated by about 0.5mm. Due to the 60 degree angle with the pivot point the plunger must slide. As the hole wears deeper I think the plunger movement will become impeded. The tensioners must be able move continuously to allow the relatively different rates of thermal expansion between the aluminium engine and steel timing components.

The latest tensioner has the plunger at a better angle so there is very little sliding action. The latest guide's steel insert will also resist wear much better.

New tensioner and blade. Plunger action is close to 90 degrees from the blade pivot so very little sliding at the contact point.


Please let me know about your experiences if you've followed this particular Jaguar Procedure.

 

There should be an image showing plunger wear on the tensioner blades towards the end of the previous post. It disappears between editing and posting it up. Weird.