It is a very complex structure to work with and in particularly with the 
Timing Chains, only special tools designed for working on the 3.7L engine will suffice to undertake the task in order not to damage the engine. As an interference engine the timing chain if snapped this can lead to valve and possibly piston damage, it requires 
Cylinder Head removal. Due to the complexity of the timing system, a slight mistake can cause a lot of damage to the engine, thus, they should only be done by highly qualified personnel, and it is always good to cross check all the repairs done before starting the engine. Two special camshaft holding tools (manufacturer tool no. 303-1248) are required for the operations described). Before camshafts can be taken out, the valve clearance should be checked, at the same time the primary timing chain and camshaft VCT unit is to be taken out. To examine hydraulic lifters, one has to first remove camshaft caps while paying attention to their arrangement; after this, camshafts can be pulled out of the cylinder head. Lifters should be removed with magnet and the same placed in a container marked for assembly after the end of the test. After camshaft removal they should be cleaned and checked for wear or damage before Guage dimensions are taken to determine if they meet their specifications. If one finds the camshaft lobes intact and in good condition then it is possible to reuse them. Proper alignment of the crankshaft before application of lubricants on the lifters and camshafts as well as re-fixing the seals that go well with lifters and camshafts. This is done by tightening the camshaft bearing caps in the correct order and also by further adjustments of the valve clearance. Before going ahead with the VCT units and the primary timing chain, the camshaft holding tools must be fitted. The same is true for the 4.0L engine procedure which is quite elaborate and involves the use of special tools and engine pull out. It entails such tasks as, dismantling involving taking off of valve covers, measuring of camshaft end play, loosening of bearing cap screws, and making sure all parts are replaced in their respective positions. During inspection, horn and camshaft journals and lobes are inspected for signs of wear and when this is done, camshaft journals and lobes are measured in relation to their specified measurements and replaced if not as required. Oil clearance checks are made with the use of Plastigage, and should the clearances be large, then the cylinder head has to be replaced. If any had been taken out, they had to be replaced on the same position and then lubricated before having the camshaft caps tightened to the recommended torque setting.