The North American version of this engine suffered from several serious reliability issues over its lifespan.
Cylinder head cracking was very common in early models, but affected all model years. Compared to the relatively stout European heads, the North American 2.9 had apparently been subject to a reduction of material around the valve stem guides and rocker shaft mounting pedestals. Some engines would suffer from this failure after overheating only once, while some would fail without overheating at all.
The block and heads underwent a redesign for the 1989 model year
, receiving additional material in some problem areas. This helped to reduce the chances of this specific failure, but it was still an issue. Some of these head castings are supposedly printed with the "89TM" designation, but there has been no verification of these claims as the "86TM" designation is usually found on the 1989 and newer heads as well. The redesigned heads also have larger diameter bosses for accessory mounting than the 1st design heads.
After-market heads are also available from World Products, with better design improvements to the early OEM design. These heads use the early model narrow bosses for accessory mounting, so fitment of 1989 and newer accessory brackets will require modification.
Hope this helps.