Sounds a bit off.
Where is the oil leak?
Front, back or side of engine.
If in the front then mechanic didn't get a good seal on the oil pan/timing chain cover gasket or on the front main seal.
Why was the timing chain replaced?
That is one thing on the 4.0l OHV engine that rarely needs to be replaced.
Water pumps do need to be replaced as normal wear and tear
Radiators can last the life of the vehicle if coolant is changed every 2 years, but still not an expensive repair.
Bearings have nothing to do with 'lack of power' they will make a knocking sound similar to exhaust leak, but engine will still have normal power.
Same with harmonic balancer, it won't effect power.
First sign of a bad balancer is a squealing from the fan belt(serpentine belt), and if you look at the balancer with engine running you can often see it wobbling, or look at the belt tensioner and you will see if 'jumping' up and down
If timing chain was installed one or two teeth off then you would have a lack of power since compression would be lower, slow to rev and general lack of power at all RPMs.
Compression test should show 160+psi per cylinder, if you get 120psi or less then timing chain is wrong
Mechanic could have broken harmonic balancer when removing it to do the timing chain, have seen some use the wrong type of puller(jaw puller) to get a balancer off which can break it.
Harmonic balancer is made up of two pieces of steel, a center hub and an outside ring, these two pieces are held together by a hard rubber "gasket", this rubber absorbs the engine vibrations, when you need to remove a balancer you must pull it off using the hub, there are threaded holes in the hub just for that purpose, if you use a Jaw type puller on the outside ring you can break the rubber gasket holding the two pieces together, when it is re-installed it is no longer "balanced" and causes a wobble and vibration, which could cause front main seal to start leaking.
I doubt he could hurt the bearings, but unless you noticed a knocking I doubt there is a bearing problem.
Last edited by RonD; 08-17-2014 at 12:01 PM.