Jaguar XK8 Timing Chain Tensioner Problems
On the 4.0 V8 built before mid-August 2001, the plastic upper (secondary) chain tensioners crack and drop their shoe, and the chain can jump or snap with no warning at all. I'd read the engine number first, then take a cam cover off and look — fitting metal-bodied tensioners costs a fraction of an engine.
How bad is it · Garage, carefully
Drive gently and book it in — don't put it off
When an upper tensioner lets go, the chain jumps teeth or breaks and the engine can be scrap. Often there is no noise beforehand, so a quiet engine proves nothing.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
Plastic upper tensioners cracking and losing their shoe
The bodies of the original upper tensioners are plastic. Heat cycles make them brittle; they crack at the barrel and the shoe breaks away, then the chain runs on metal, slackens, jumps a tooth or snaps — and a loose piece can wedge between chain and sprocket.
A rattle lasting a second or two after a night standing, gone once oil pressure builds; rough running from timing knocked out. Just as often nothing at all until it fails, at anything from about 30,000 to 130,000 miles. When there is a warning it can be a rattle each time the revs fall back to idle, rough idle below about 1,000 rpm or stalling in traffic once a tooth has jumped, or the oil pressure light flickering for a second a week before the engine stops with a metallic bang.
Take off the cam covers and look at the upper tensioners: red, brown or white plastic bodies need replacing, metal bodies are the later design. Look for cracks at the barrel and a missing shoe. Look before you buy parts: on a car with an unknown past, metal tensioners may already be fitted.
Fit metal-bodied tensioners, C2A 1511 and C2A 1512, with the shorter bolts JFB10607E and new cam cover gaskets. For example about $250 doing it yourself with cam locking tools, or about £300 at an independent — against about $10,000 for an engine. New cam cover gaskets go on with the job and also stop oil collecting round the rear plugs. If the engine has stalled and won't restart, move it on a flatbed, not on a sling. After a chain has jumped, a dealer's new-engine verdict isn't final: chains, tensioners and the bent valves can be renewed by an independent for far less.
Cracked chain guides and lower (primary) tensioners
The guide rails are a metal core in plastic, and the lower tensioner blades are plastic too; both crack with age, even when the engine sounds perfect. They are less often catastrophic than the uppers, but a broken guide can jam a chain.
A rattle that is still there after new upper tensioners; a slack lower chain; or nothing, found only with the front open.
The lower tensioners can be glimpsed with a telescopic mirror through the cam cover openings. There must be no slack in the primary chain.
With the front cover off, renew the lower tensioners, guides and rails at the same time — labour dominates the bill. For example about $2,000 for all chains and tensioners with a water pump.
A chain job put together wrong
New parts don't help if the cam timing is off a tooth, the bolts don't clamp, or the parts are cheap. The long bolts for plastic tensioners bottom out before they tighten a metal one.
Trouble that starts after the work: a misfire on one cylinder at idle, a check engine light, P1396, tapping that grows into a rattle, or a chain that breaks within a few hundred miles.
Have the cam timing on the affected bank checked against the locking tools, and the tensioner bolts checked for length and torque. Look at the variable valve timing solenoid pins for damage. While the sprocket bolt is tightened, the run on the fixed-shoe side of the tensioner must be held tight — the top on the right bank, the bottom on the left.
Correct the cam timing on that bank, refit the tensioner with the correct bolts and thread-locker, and use one-piece chains rather than ones with a joining link. If the shoe had already gone and the chain ran on metal, a new tensioner on the old chain is a gamble — the chain can break within weeks.
Cam tick or a belt, not the tensioners
Not every cold-start noise is the chain. The cams tick when cold, and the accessory or supercharger belts can tick in time with the revs.
A light, even ticking that follows engine speed and fades as it warms, with tensioners known to be new or metal.
Listen with the belts off for a moment, or have the noise heard from cold — it has to be cold to be heard. Ask to see the old tensioners after any job.
New accessory and supercharger belts can stop a front-of-engine tick. Cam tick is harmless; a fully synthetic 5W-30 can quieten cold-start chatter.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Read the engine number, not the VIN or model year
Engines numbered 0108130000 and later (built from 13 August 2001) left the factory with metal-bodied tensioners; the number is a date code, YYMMDDHHMM. Model year isn't a guide — many 2002 cars have them, some don't, and engines get swapped.
freeListen to a dead-cold start
After a night standing, a rattle for a second or two before oil pressure comes up points at tensioners. Silence does not clear them.
freeTake a cam cover off and look
Remove the intake to the throttle body, the coil cover and coils, then the cam cover bolts from the outside in. Plastic upper tensioners get replaced; metal bodies are fine, though their shoe is still plastic.
a cam cover gasketFit metal-bodied upper tensioners
Ask for C2A 1511 and C2A 1512 with the shorter bolts. Plastic-bodied tensioners are still sold as new — refuse them. The uppers come out with the cam covers off and the cams locked; book time is about four hours. Plastic versions carry part numbers starting NCA, the metal-bodied ones C2A — check the box before it goes in.
about $250 DIY, $800 at a shopOnly with the front open, do the lot
If the rattle survives new uppers or a chain must come out, renew lower tensioners, guides and chains together. If a shoe was lost and metal touched the chain, change the chain, oil and filter too. With no rattle and sound chains, uppers alone have carried an engine from 60,000 to 190,000 miles.
around $2,000What it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XK8 Turns Over But Won't StartIf the engine cranks but will not fire — a snapped upper chain is one of the causes.
- Jaguar XK8 Restricted Performance, Limp ModeIf a misfire or Restricted Performance came on and the timing is known good.
- Jaguar XK8 Nikasil Engine ProblemsThe same early engines have Nikasil bores until August 2000 — the engine number tells you which.
- Jaguar XK8 OverheatingIf the engine runs hot or loses coolant — the water pump is often renewed along with the chains.
- Jaguar XK8 Oil LeakThe tensioner job means new cam cover gaskets — and a leaking cam cover is the usual XK8 oil leak.
- Jaguar XK8 Misfire, Coil Packs and Spark PlugsIf the engine misfires but compression is even on both banks — coils, plug wells and plugs come first.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.
