High mileage doesn't necessarily require a major overhaul, while low mileage doesn't guarantee you won't need one.
Heavy oil consumption indicates that attention should be given to piston rings, valve seals and/or valve guides. Before deciding that rings and/or guides are bad, make sure there are no leaks.
Check the oil pressure with the gauge installed in the oil pressure test assembly and compare it with the value specified in the specification.
If it is too low, the bearings and/or oil pump may be worn out. Loss of power, noticeable valve noise and high oil and fuel consumption can also indicate the need for an overhaul, especially if all of these problems are present at the same time.
In the process of overhaul, the pistons are removed, and the holes are drilled and honed. New pistons are required to enlarge the bores. The main bearing, the bearing of the upper head of the connecting rod and the camshaft bearings are usually replaced with new ones, if necessary, the crankshaft is ground to restore the journal surfaces. Valves are also serviced if their condition is noticeably worse compared to other nodes. When overhauling the engine, other units should also be sorted out - a generator, a starter, a distributor.
Note: unreliable elements of the cooling system - hoses, drive belts, thermostat, water pump must be replaced with new ones during engine overhaul. The radiator should be carefully checked. It is not recommended to repair the oil pump (except 3.8L) - a new one should be installed when the engine is overhauled.
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