Aluminium twin-cam straight six built from 1984 to 1996 in 2.9, 3.2, 3.6 and 4.0 litre forms for the XJ-S and the XJ40 saloons. Like the V12 it is a bare-alloy engine with black cam covers, but it adds a black painted inlet manifold. This is the thinnest of the three Jaguar pages: one judging guide covers the 3.6 in the XJ-S and nothing found covers the XJ40 at all.
Also known as: AJ6, AJ16
Records
Bare natural aluminium
AJ6 3.6 · 1984–1991 · block, unpainted
Awaiting measurementB · Club verifiedLast verified 2026-09-20
Awaiting measurement
Not yet measured. The patch will appear once a spectrophotometer reading is recorded.
The judging guide's phrase for all types covers the V12 and the 3.6 six it shared the XJ-S engine bay with, so the block, cylinder head and timing chain cover are all bare aluminium and no separate component records have been made for them. The record's range stops at 1991 because the guide does, and starts at 1984 because that is when the guide's 3.6 entries begin. No judging guide or club technical page covering the XJ40 was found, so nothing on this page is sourced for the saloon; the models are listed in applicability because a retailer's parts list shows the same camshaft cover gasket serving both cars, which establishes a shared engine and not a shared finish. The retailer's own date range for the XJ-S AJ6 starts in 1982, two years before Wikipedia's, and their page carries a disclaimer that its year ranges are a guide.
Sources
judging-standard:JCNA, XJ-S 1976 to 1991 Judging Guide, Engine Block, Head, Intake and Plumbing — Gives block colour as natural finish aluminium for all types and cylinder head colour as natural aluminium for all types, the guide's types being the V12 and the 3.6 six; the timing chain cover is natural aluminium, the six-cylinder water pump aluminium, and the block core plugs cadmium plated rather than painted
community:Wikipedia, Jaguar AJ6 engine — Gives the 1984 to 1996 span, the 2.9, 3.2, 3.6 and 4.0 capacities, the cars and years each went into, and confirms the block is aluminium
retailer: Ashwood Jag Parts, camshaft cover gasket EAC2912 — Lists one gasket as fitting XJ40 XJ6 3.2, 3.6 and 4.0 from 1987 to 1994 and XJS 3.6 and 4.0 AJ6 engines from 1982 to 1994, used here for model applicability only and not for any colour
History
2026-09-05 · Draft researched from public sources; unverified
2026-09-20 · Judging guide claims checked against the guides' own text; published
Machined ribs, not painted ones: as on the V12 and the ribbed XK six covers, only the background is black. No sheen is stated for the AJ6 cover anywhere found, so gloss is this site's default and not a sourced fact; note that the JCNA Series 3 E-type guide does commit to semi-gloss for the V12 cover, which makes gloss here a guess rather than a likelihood. The badge changed at some point from the C35732 label the judging guide records to the EBC3888 emblem a retailer lists for the 4.0, and nothing found dates that change. The 4.0 cover is not described by any fetched source.
Sources
judging-standard:JCNA, XJ-S 1976 to 1991 Judging Guide, Cam Covers — Gives the 1984 3.6 cover as black with machined ribs and a Jaguar label, part number C35732, at the front centre, held on by six cadmium plated Pozidriv screws with copper washers; the V12 covers in the same guide take the same label part number
retailer: XJRover, cam cover emblem EBC3888 — Lists a cam cover emblem for the 4.0 AJ6 engine in the XJS, XJ6 and XJ40, used here for applicability only; the listing gives no colour or finish
History
2026-09-05 · Draft researched from public sources; unverified
2026-09-20 · Judging guide claims checked against the guides' own text; published
This is the one place where the AJ6 differs from the V12 it shared a showroom with, and the guide states both in the same sentence, which is as clean a comparison as this research produced. It is an inlet manifold, not an exhaust manifold; the schema has one component for both. The record covers the XJ-S 3.6 only, because that is the only car the source describes. No shade, code or sheen is given for the black and none has been guessed.
One judging guide carries this page, and it is worth saying so before anything else. The JCNA XJ-S guide covering 1976 to 1991 was written for a car that could be had with a V12 or with the 3.6 litre AJ6, so it describes both engines side by side, and it is the only document we have found that describes an AJ6 at all.
What it says is that the block is natural finish aluminium and the cylinder head natural aluminium, for all types, by which it means the V12 and the six. The timing chain cover is natural aluminium, the six-cylinder water pump is aluminium, and the block core plugs are cadmium plated rather than painted. So on an AJ6, as on the V12, the castings are bare.
The cam covers are black with machined ribs and a Jaguar label, part number C35732, at the front centre, held on by six cadmium plated Pozidriv screws with copper washers. The same label part number serves the V12 covers in the same guide.
The one genuine difference between the two engines is the inlet manifold. The guide gives it in a single sentence: the V12 manifold is natural aluminium and the 3.6 manifold is black painted aluminium. That is the only painted casting on an AJ6 besides the cam covers.
What changed, and when
Nothing that any source dates. The AJ6 ran from 1984 to 1996 in 2.9, 3.2, 3.6 and 4.0 litre forms, and the only change we can point at is on the cam cover badge: the judging guide records a Jaguar label with part number C35732, while a UK parts supplier lists a cam cover emblem, EBC3888, for the 4.0 engine in the XJS, XJ6 and XJ40. Something changed between those two part numbers and nothing found says when or why.
The 4.0 litre engine that replaced the 3.6 in 1989 is not described by any source we have found, and neither is the 2.9 or the 3.2.
Common mistakes
Painting the block and head. The same reflex that gets alloy V12s painted black gets AJ6s painted black, and for the same reason: a bare alloy casting that has been hot for thirty years looks unfinished. A black AJ6 block is somebody's decision, not Jaguar's.
Painting the ribs on the cam cover. They are machined bare; only the background is black.
Assuming the inlet manifold matches the V12. It does not, and this is the one place where a six and a twelve sitting in the same model of car were finished differently.
Assuming an XJ40 is an XJ-S under the bonnet. It may well be, and the parts catalogues suggest the engines are close enough to share a camshaft cover gasket. But sharing a gasket is not evidence of sharing a finish, and nothing on this page is sourced for the saloon.
What to buy
Black, for two parts: the cam cover background and, on the XJ-S 3.6, the inlet manifold. No source states a sheen for either. The V12 guide gives semi-gloss for the equivalent cam covers, so satin is the better bet, and both satin and gloss engine enamels are listed on the records above. An inlet manifold runs far cooler than an exhaust manifold, and ordinary engine enamel is well within its rating there.
Leave the block, the head and the timing cover bare, and clean them.
Nothing is disputed here, because there is not enough published to disagree with. What this page has instead is a hole where the XJ40 should be.
No JCNA judging guide for the XJ40 was found. The Jaguar Enthusiasts' Club offers technical support through named experts rather than a public technical library. Forum threads on the AJ6 that turned up in searching are about gaskets, bolt torques and oil leaks, and none of the ones read discusses the original finish of anything. So the XJ40 appears in the applicability lists on this page only because a retailer's parts list shows the same camshaft cover gasket serving the saloon and the XJ-S, which establishes a shared engine and nothing more.
Two smaller gaps are worth flagging. The sheen of the cam cover black is not stated anywhere for the AJ6, and this page defaults it to gloss even though the equivalent V12 guide commits to semi-gloss, so that default is a guess rather than a likelihood. And the guide's coverage stops in 1991, five years before the AJ6 did.
Finding original paint on your own engine
The AJ6 was still being built when the cars it went into were ordinary used cars, so the paint you find is more likely to be someone's tidying-up than a period respray. Look at the inlet manifold first. An original black manifold shows crisp casting numbers and clean machined faces; a repainted one has black in the lettering and over the flange edges.
On the cam cover, the machined rib faces are the tell. Original black stops at the machining and does not creep onto it. Where a cover has been sprayed on the car, the black usually runs into the rib valleys unevenly and covers the label surround.
Because this page is thin, a photograph of an unmolested low-mileage XJ40 engine bay, or a page from an XJ40 parts catalogue giving cam cover part numbers with finishes, would be worth more than anything currently on it.
If you own an unrestored XJ40 or a late AJ6 car, a photograph of the engine bay would fill the largest gap on this page. Send it to us.
Every record above has a correction link. Applied corrections are logged on the record and on the changelog with their source and date.