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http://www.luxurycoachlifestyle.com/...checklist.html ( Inspection Checklist)
Displacement 391 cu in (6.4 L)
Bore 4.052 in (102.9 mm)
Stroke 3.784 in (96.1 mm)
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[TD="class: copy"]There is a field problem with two popular engines in the medium duty field. They are the Ford truck 361 and 391 cubic inch displacement engines.
The 361 and 391 are the same engine, with a slight increase in stroke accounting for the difference in displacement. There have been two problems that have come to our attention. The first is an overheating condition that shortens the life of the engine below normal expectations, and the second is excessive oil consumption past the valves.
OVERHEATING PROBLEM
In regard to the overheating problem, extreme care should be taken to maintain 100% efficiency in the cooling system at all times, as it is evident that this is barely sufficient in many cases, even when in the best possible condition. The radiator should be kept entirely clean of insects, debris, and dirt which may affect the flow of air through the radiator core, and be flushed regularly, and protected with a rust inhibitor (Stop-Rust) at all times.
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Where the climate is extremely warm, a low temperature thermostat should be installed. Retarded timing also contributes to overheating, so engine timing must be periodically checked. Of course all the usual cooling system parts - water pump, fan belts, and hoses--should also be watched and kept in good repair. Due to the heat problem these engines should not be rebored over .030.
VALVE GUIDE OIL PUMPING
The oil going down the guides is a simpler matter. The installation of our P.S. valve seals will completely eliminate the excess oil going down the guides. We have found some engines consuming a startling amount of oil past the guides. At the time of seal installation the intake manifold gaskets should also be carefully checked, as this is also a potential source of oil entering the combustion chamber in the valve area.
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