Jaguar AJ34 (AJ-V8, 4.0 and 4.2)

Jaguar's 4.2-litre V8, naturally aspirated and supercharged — the engine of the XJ, XK, S-Type R and early XF, and the direct predecessor of the 5.0 AJ133 that replaced it.

Its known weakness is the timing chain tensioners, which on the earlier 4.0 and 4.2 engines were plastic and degraded, allowing the chain to slacken. The presentation is a rattle at start-up progressing to timing codes and, if ignored, a jumped chain. Revised metal-bodied tensioners exist, and whether they have been fitted is the most valuable single fact about a given engine.

The second item is the Nikasil cylinder-bore coating on the earliest V8s, which the high-sulphur fuel of some markets attacked — the same problem BMW's M52 had, and largely historical now since affected engines were replaced. On the supercharged versions the intercooler pump and the supercharger's coupling are the two items that determine whether the car makes its power.

⚑ The AJ26 and AJ27 are 4.0 and the AJ34 is 4.2, and this page carries all three. A capacity quoted for the AJ-V8 is quoting one of them, which is worth settling before any parts search.