This is about the upper timing chain tensioner on the AJ6/AJ16 6 cylinder inline engines (X300/XJ40/XJS), NOT about the upper timing chain tensioners on the AJ26/27 V-8 engines (X308/X100/X200).

I read a number of comments on the Internet where people assumed that just because they have the updated upper tensioner (on the AJ6 or AJ16 6 cylinder engines) that those tensioners would not fail...

I have a 1996 XJR with the AJ16S supercharged engine. A few months ago it started to rattle sometimes when being started (cold or hot). Also I noticed a sound when going up the hill at 1500-2000 RPM - like many other people. In my case, the sound only occurred when the engine was loaded (the XJR not cruising). Since then I had minimized the number of starts (used the XJR mainly for long distance driving) as not to wear out the timing chain guides, in case the upper tensioner was defective.

So - two likely culprits:

Exhaust system - mainly catalyst heat shields. This was the initial suspect as the engine load, and thus exhaust volume and velocity, made a difference in the occurrence of the buzzing sound.
The front catalysts do not have heat shields, but the center one does. This heat shield (in my case) was tack welded on the front, but was floating at the rear (no support), meaning that it could resonate and create a buzzing sound. I inserted three small spacers made of exhaust fiberglass wrap, keeping the heat shield separated and isolated at the rear of the catalyst while preventing it from resonating. This resulted in some reduction in the sound going up the hill.

Upper timing chain tensioner - Having an engineering/science background I thought about whether the engine load should affect timing chain slap. Initially I though that this would be a minor effect, only due to the difference in the actuation of the valve train (more air flowing in/out via the valves -> very minor difference in the power required to turn the camshafts). Thinking more about this, I realized that the resonance in the chain (causing chain slap) is most likely created by the force pulses of the engine. Under light load (cruising/deceleration), the force pulses from the combustion part of the cycle get absorbed rather well by the flywheel/flexplate/harmonic damper and drive train rotational inertia. However, under load, the force pulse become much more powerful and thus the harmonic distortions (-> crankshaft flexing torsionally as well as longitudinally) increase also. This can set up a resonance / standing waves in the timing chain (which already naturally resonate to some degree). -> engine load can definitely affect timing chain noise.

I removed the camshaft cover (since the XJR already has the updated tensioner from the factory -> cannot retract and secure the piston, danger of it dropping into the crankcase/timing cover - see TSB). I then removed the camshaft position sensor/CPS (making sure that the engine was with cyl. 1 at TDC -> round area is visible through the sight glass bubble, and marking where the retaining bolt was holding the CPS).
I then carefully removed the upper tensioner, pushing the upper timing chain guide toward the outside of the engine (right side) and extracted the upper timing chain tensioner with the piston in it from the engine.
The upper timing chain tensioner had very little wear, probably due to me not driving/starting the car much with this issue.
I then installed a new tensioner, using Hylomar (not Hylosil) on its gasket and then assembled the parts back together. Finally, I removed the fuel pump relays (per the TSB) and cranked the engine to get the tensioner to 'activate'. After I reinstalled the fuel pump relays, I started the engine: no timing chain noise whatsoever. Not a loud rattle, not a slight buzz. I still have a minor buzz at 1500-2000 RPM - others who updated the tensioner (and in some cases all of the timing chain related parts) also still have that sound. This may simply be the nature of the AJ16 engines -> some timing chain resonance at that RPM range. But I would say it's 80-90% quieter (1/5th to 1/10th as noisy).

I inspected the tensioner -> the piston has visible score marks near the end, possible from being deflected by the timing chain guide pressing against it at an angle (the tensioner should really have been mounted orthogonally/right angle to the guide, but it's at a right angle to the engine block face, while the guide is at a 'sloping' angle). The scoring means that the piston does not freely move in the tensioner bore and can stick.

So while the original tensioner design (with the Allen bolt in the center and the hold down clamp) had issues with its oil supply, both (new/redesigned (up arrow visible on tensioner) and old) appear to encounter mechanical failure due to scoring of the piston.

Higher quality oil (mostly mixed fleet 5W-40 synthetics (Delvac 1, Rotella T6, etc) and other synthetics such as Mobil 1 0W-40, GC Castrol 0W-30, Pennzoil Ultra 5W-40) may reduce the scoring, but I think that this is a minor design defect with the otherwise great and indestructible AJ16 (and AJ6) engines. I think replacing the upper tensioner every 60-70 K miles may not be a bad idea.

I will upload pictures of the scored piston in the next few days.

Christian

Also check out this article:
"Cam Chains – Cam chains can take a beating from the torsion peaks. Same for cam
gear drives. The vibration motion tries to make the cam drive do the same motion and
jerks the chain back and forth. If this motion gets through to the cam, it doesn’t help
cam dynamics and can also show up in the spark scatter with cam driven distributors."
Author: William C. Sisco, for BHJ Dynamics
http://www.bhjdynamics.com/downloads...amper_Info.pdf

 

Thanks for the feedback.

Photos of the tear-down (i.e., how to replace) would be more beneficial than the scored pistion

Did you replace the lower tensioner, along with the piston and upper tensioner?

 

Since I only replaced the upper tensioner not much of a tear down was required. I did not take pictures, but here are the steps in order:

1. Place traction control cable (if equipped) out of the way
2. Disconnect breather hose from camshaft cover
3. Disconnect air hoses from electric secondary air injection pump
4. Unbolt secondary air injection pump and place out of the way
5. Rotate engine (I used starter, can use socket on crankshaft/balancer/pulley bolt instead - only rotate engine in normal direction of rotation, NOT backwards) until cylinder 1 is at top dead center -> round depression is visible inside circle of camshaft position sensor (below where the air injection pump sits)

Do not rotate engine after this step.

6. Unplug electrical connector and remove hold-down bolt from camshaft position sensor - mark position on sensor using a Sharpie or other felt tip pen first. Rotate camshaft position sensor (without pulling it out) so that it will clear engine block and components. Pull camshaft position sensor straight up -> the round depression will rotate - this is expected. Place camshaft position sensor in a clear location, without rotating the gear. Optional (I did) coat gear with moly based assembly lube (shouldn't be necessary since gears should be broken in, but can't hurt)
7. Remove top plastic cover from camshaft cover (three torx bolts)
8. Unbolt coils from camshaft cover (6*2 hex bolts). Unclip wiring from retainers (on camshaft cover). Place coils and wiring harness out of the way - no need to disconnect coils from harness. No need to remove spark plugs - if spark plug change is desired, then perform following reassembly or plug spark plug holes with clean shop towels to avoid dropping items into the combustion chambers.
9. Remove 13 hold down bolts (torx - different torx size that the three torx bolts mentioned above)
10. Carefully break the seal of the camshaft cover to the cylinder head (it will be stuck, don't hammer it and don't score the mating surfaces). Remove the camshaft cover.
11. Unbolt and remove the two hex bolts on the upper timing chain tensioner.
12. Using a long screwdriver carefully push the upper timing chain guide toward the outside of the engine (right side as when looking toward the front of the car)
13. Very carefully and gently (making sure that the piston comes along and does NOT fall out) remove the upper timing chain tensioner.
14. Lubricate new timing chain tensioner - I pulled the piston out, and covered it with a mixture of fresh engine oil and moly based break-in lube (did not want to use 'full strength' moly lube - it is sticky and might prevent the piston from moving, though the oil pressure should really force the piston out, regardless). Optional: Paint outside of new timing chain tensioner (making sure that no paint gets on the inside parts (mating surface, outside of cylinder including O-Ring, piston) - I did paint it, since they do start to develop surface rust (cast iron part)
15. Cover upper timing chain tensioner gasket on both sides with a thin film of (blue) Hylomar gasket/flange dressing, then place on engine block.
16. Carefully insert new upper timing chain tensioner into engine block, making sure that arrow points up. Also, the guides on the piston need to be vertical with respect to the engine (not the tensioner) to ensure that it engages the timing chain guide properly. Tighten bolts using torque wrench to specified settings.
17. Reinstall camshaft position sensor. Place it in the same position that you used the pull it out. Once seated, rotate it back to align the marks (made with the felt tip pen) with the hold down bolt. The round depression should now be visible through the circle on the sight glass.
Reconnect electric connector - if you forget this, the engine will take a few rotations before it starts as the ECU tries to figure out combustion/exhaust stroke timing - which it can't from the crankshaft position sensor alone.
18. Turn camshaft cover upside down - use engine flush or similar solvent to clean (hidden) breather wire mesh filter (perfect opportunity since camshaft cover is off). Pour solvent out of camshaft cover (let it all drip out). Dispose of solvent responsibly and in an environmentally friendly manner - one solution may be to mix and recycle it with use oil.
19. Replace camshaft cover gasket/seal (1), camshaft cover spark plug seals (6), and camshaft hold down bolt seals (13). Reassembly is reverse of disassembly. Use Hylosil or equivalent on the half-moon seals at the back of the cover. Clean/degrease all mounting surfaces first using solvent. Use torque wrench to tighten to specifications. Follow (other TSB or shop manual) for tightening sequence of camshaft cover hold down bolts. This other TSB also has updated torque values for the camshaft cover hold down bolts. Do NOT overtighten. Note: The camshaft cover gasket/seal may be difficult to install. I ended up placing it on the cylinder head, and then lowered the camshaft cover staring from the back (where the half-moon seals are) positioning the gasket top (inverted T shape) into the channel on the camshaft cover. This was no fun, but I got it in properly after about 20 minutes or so.

If you want to replace the spark plugs, then now is a good time. Though I prefer to fix one thing at a time to reduce issues that may need to be tracked down.

20. Install new (or reuse if still good) coil gaskets. Install coils and tighten hold down bolts to spec. Do NOT overtighten. Place wiring harness back into retaining clips.
21. Replace plastic cover. Tighten torx bolts to spec. Do NOT overtighten.
22. Reposition traction control actuator cable. Reinstall air injection pump, reconnect hoses.
23. Remove fuel pump relay (or two relays for XJR6 - should not need to remove second one, since it only turns the fuel pump on above 4000 RPM, but better to be save). Crank engine over until oil warning light turns off. If you hear any noises, stop immediately and investigate.
If no noise, crank engine over a few more times to ensure that piston releases ('pops') pushing the timing chain guide against the chain
24. Reinstall fuel pump relay(s)
25. Crank engine over - engine should now start smoothly without any timing chain rattle.
26. Drive the car! Two reasons: a) Enjoy your quiet AJ16 engine and b) a hot engine will help evaporate any remaining solvent in the breather mesh filter in the camshaft cover -> get's burned with the blow-by/oil fumes.

I think that's about it. If anybody sees something that I might have missed, please let me know.

I am intentionally not listing the torque values and tightening sequences. Please make sure to have a copy of appropriate TSBs (available on AllDataDIY.com and other web sites) and preferably the shop manual as well.

And, again, do not overtighten the bolts. The only bolts that have a relatively high torque are those holding the tensioner in place. All of the other bolts have a rather low torque spec.

I did not replace the lower tensioner or any of the guides. The guides that I could inspect had minimal wear. Replacing any of the guides (apart from the top horizontal damper) or the lower tensioner requires removing the timing cover -> all belts, alternator (I think), pulleys/balancer, etc. have to come off. Some people did this and replaced the timing chain (to completely eliminate the resonance at 1500-2000 RPM) only to find out that it did not help (see above post for potential reason as to why). On the other hand, some people found damaged components/loose bolts when they removed the timing cover.
I anticipate redoing the entire timing setup in another 60-70K miles (together with another new upper tensioner) - My XJR right now has slightly of 70K miles on it.

P.S.: AJ6 engines similar, but minor differences due to ignition system (distributor instead of camshaft position sensor and spark plug wires instead of coils-on-plugs) and camshaft cover design

Christian

 

Well written Christian.

I did mine at 168000kms, and it also was the "update" unit, and very sad internals.

Very silent also for about 5000kms, then back again, bugga.

Notrd the blades visible from above being very sad, so timing cover off, and found the oil pump chain damper set tooooo far from that chain, by a long setting gap, so reset that, removed the lower tensioner, and replaced the piston assembly (very sad also) and ALL the guides and dampers. Chains replaced other than the single row oil pump chain, due to sump off to do that, NAH.

Quiet as you could wish.

Mine was plain and simple very shoddy oil change scheduling, although the books are all duly stamped and the PO charged for Semi-Synthetic oil etc, but alas no such fluids in this engine up until my owhership. The huge amounts of carbon/dried sludge were almost unbelievable, so "elcheapo oil" I suspect.

Now 181000kms and no noises apart from a slight power steer pump "whir", which I will live with. NO 1500rpm type noise at all.

I run 10W/40 Synthetic oil and 8k kms change intervals.

 

The piston (see attached pictures or pictures in my photo album) shows a variety of wear scars.

a) short deep scars and pitting near the 'inside' edge of the piston - possibly due to being deflected by being 'pushed' down by the angled timing chain guide

b) long scars - possibly due to the internal ratcheting mechanism failing (piston retracts completely when oil pressure bleeds down)

c) a deep and wide scar/gouge in the piston face - likely from the timing chain guide being not being orthogonal to the piston face, but instead at a oblique angle

So, without an in-depth failure analysis I have the following hypothesis.

Two separate failure modes.
1. The piston ratcheting mechanism potentially failed, causing the long wear scars (piston extending/retracting completely on repeated startups). This extension/retraction may also have contributed to the gouging of the piston face by the timing chain guide.

2. The timing chain guide deflecting the piston, causing the short scars and pitting at the inside edge of the piston.

I noticed that the fit between cylinder and piston is not extremely tight on both the old and new tensioner assemblies. This contributes to the piston cocking in the cylinder bore. The reason for the not so tight fit may be either not the highest quality manufacturing, or it may be intentional to handle thermal expansion difference between the piston and the cylinder bore (different materials).

 

Awesome write-up, Christian.


This thread should qualify as a sticky ... Moderator???

 

Yup, good call . I will add them into the FAQs

 

Thanks for the feedback on my post. Btw. do you want to also add it to the FAQs for the XJ40 and XJS? - those with the AJ6/AJ16 engines of course have the same tensioner (issue)

 

Thanks for the reply , I didn't realize these engines also use same tensioner .Then it makes sense to add this into their FAQs

 

Hi,

Firstly thanks to Christian for this thread as it is very informative. I am about to replace my upper tensioner (the original type) with the new updated tensioner (part NBC2031AA) so I have been trying to do as much research as possible before doing the job. I've also read the TSB that was issued.

The main bit I am not sure about is the release of the tensioner piston. The TSB says to turn the starter and the movement of the chain against the tensioner blade and piston will release the mechanical tensioner. And in Christian's post above he refers to the piston release (or pop).

I have attached a photo of my new tensioner. Obviously there is a piston that goes in the housing. Firstly I am a bit worried the piston could just fall out inside the engine or maybe this can't happen because it will too close to the tensioner blade. And secondly does something mechanical 'release' from the bottom of the piston once the motor is turned over? Otherwise what will hold the piston out when there is no oil pressure? And how will I know if it has released - does it make a definite sound?

Any comments would be appreciated.

Regards
Mark

 

Sorry it seems my picture did not load correctly

 

Marke,

Either way will work to "fire" that piston.

Since the cam cover is off I would use a LARGE screwdriver and simply "pre-fire" the piston.

With all the in and out of my "new" tensioner in the early days, I simple got "lazy", and let the slap of the chain actually fire the piston, BUT, the rattle was certainly scary as hell for that split second.

 

Hi Grant, thanks for the reply. I have previously read your posts regarding the work you did replacing all your timing gear.

At this stage I hoping to be a bit lazy and replace the tensioner without removing the cam cover as I have the original tensioner that can be wound back. My start up rattle is fairly intermittent but i do get the 'buzz' at 1500-2000 rpm under load as you described.

I have purchased the full kit of chains and dampers etc but if the upper tensioner replacement solves most of my noise the rest of the job might get put off for a year or so.

So just as a final question, I assume I don't have to undo anything at the base of the new piston before installation? I note there is a small Allen Key hole at the piston base and wondered if I have to turn anything there to ensure it 'fires'

Regards
Mark

 

MARK, sorry for the "e", old age.

NO, nothing to do, simply slide it in, with a NEW o/ring and gasket.

DONT touch that allen key bit, as it will FIRE the piston, and if you are not ready for it, bits MAY fly all over the lounge room. There is a stop peg inside the outer casing to stop it coming all the way out, but mine jumped that once in all the fiddling I did, so be careful.

The allen key is used to "prime" the assembly, that is all.

The cam angle sensor (that wizzy thing where a dizzy used to live) will have to come out to do that tensioner, so lift the lid and mark the spinning plate with a texta at the window position, so refitting is as it was. OR, rotate the engine so the factory imprint in that spinning plate is in the window BEFORE dissmantling the engine.

Put a rag in the hole of the cam sensor, coz if something falls inside, you will we impressed, NOT.

Once in and secured, hit the starter, and if its like most AJ16's and cranks about 3 turns before firing that may be enough to fire the piston, so the death rattle may be minimal. The silence when it fires will give you that warm and fuazzy feeling, trust me, haha.

 

Ok thanks very much Grant. Hoping to get it done next weekend it time permits. Will let you know how it goes.

 

Job done. It turned out to be easier than expected. When removing the old original tensioner the TSB said to remove valve clamp and remove valve. Well I removed the valve clamp but wasn't sure whether the valve just pulled out or screwed out. After a google searched I realised it just needed a good pull.

Before removing the old tensioner I removed the fuel pump fuse and started the car until it run out of fuel. Then when the new tensioner was installed I cranked the car until it had oil pressure several times to be sure the tensioner fired. I wasn't game to have the car start without having already fired the tensioner.

When I started the car all was quiet. I still have the 'buzz' under load at around 1500-2000rpm which is a bit of a disappointment, maybe it has reduced a bit, it's hard to tell. But the intermittent rattle on start up seems to have gone.

Thanks Grant for your advice and Christian for starting this thread

 

Sweet.

That buzzing will be the rest of the dampers/blades in a sad state.

Sadly the buzzing may get worse, coz once these things start to wear, replacement is the only sure fire fix.

Using a good quality synthetic oil will definately keep that job on the bottom of any "to do" list.

 

Hi Grant or anyone else that has replaced their timing chains,

I am planning to replace my timing chains and dampers in the next few months. I replaced the upper chain tensioner a couple of years ago but never eliminated some of the buzz I have at 1500-2000rpm under load. I'm trying to sort out everything I need in advance to limit the time the car is parked up.

The kit I've been sitting on for 2 years has all the required chains, dampers and crank oil seal included. I intend to re-use the upper tensioner as it is only a couple of years old. I'm also going to buy a new woodruff key in advance in case I damage the old one getting it out and new cam cover seals.

I was wondering if the lower tensioner should also be replaced? Looking at the part numbers it seems there are 3 main components in the lower tensioner that may need replacing. The piston, non-return valve and o-ring. The lower tensioner never seems to get talked about as a problem like the upper one.

I've read the job description on Jim Butterworth's web page and he required a new crankshaft spacer as the old one was grooved from wear. Is this common to most cars or do you think it is a rare issue? A new spacer is not cheap.

Are there any other parts I should have on hand? The car has done 201,000km but still looks great and is used everyday

Thanks in advance

 

Marke,

The lower tentioner is different to the top unit, as in it is NOT oil pressure fed. The housing has a "funnel" type casting that collects oil from the "wet side" of the chain. The pulsing of the chain causes a build up of pressure that assists the spring to dampen that chain.

What I found was the hole that allows oil into the housing from that funnel gets clogged, so make sure it is cleaned out.

My lower piston was a tad sad, so I used the OLD piston from the top tentioner (bear in mind that mine had the update in the top prior to my intervention), and although worn, was much better than the lower old piston.

I also added a 2mm washer to the internal spring for added tention, MY decission, and NO regrets.

Firing that lower piston is a fair mongrel, so really, and I mean REALLY, take your time and make 100% sure it is fired off, coz there is NO way of getting at it once the timing cover is back on, and the chain "slap" that fires the top one will not work here. I messed it the first time.

The wear sleeve being grooved is "normal", and I strongly suggest a new one, and yes they are $$.

Polishing that ring with 1500 wet and dry paper using oil as a lube will eliminate small imperfections, and may well be satisfactory, as mine was.

Hi_Temp RTV in Grey will be needed to reseal the cover etc. Carby cleaner will be also needed for 100% cleaning of the cover etc prior to refitting.

 

Thanks for your feedback Grant, much appreciated. I will have a few more questions but I need some time to think about it all!