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Cummins boost for engine life
Page 47
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A NUMBER of design improvements and modifications have been built into the Cummins V6 and V8 range of engines.
To quieten the V504, which was developed from the V470, the rocker covers are split and rejoined with a special bond. This reduces the perceived noise by 2DBA.
Another noise reduction method which also cuts the sound by 2 DBA is the use of a clip-on acoustic panel fitted around the sump.
Cummins engineers found that using a perforated steel shell with glass wool bonded to the inside was the most effective construction.
More fundamentally, the crankshaft forgings have been revised to raise the degree of measured dynamic balance from 94 per cent to 100 per cent.
The once standard steel joints between the heads and block are replaced by laminat ed hard asbestos gaskets which have a steel bead. These McCord part-cured gaskets are said to retain their hardness despite the effects of heat, oil and pressure, and to eliminate leakage of gases or coolant.
To improve the performance . of its PTD injectors, Cummins has altered the outside cone angle of the cup.
This is said to reduce the carbon build-up and increase injector down-time intervals.
Changes to the cone angle of the plunger and the use of harder steel for the injector tip are said to improve the injectors' resistance to heat and pressure fatigue.
An impressive use of electro discharge machining at Darlington ensures that the injector spray holes are accurately made which, Cummins says, allows better fuel consumption while producing more complete and even combustion. It also brings compliance with British and EEC output ratings and emission controls.
Crankshaft oil sealing has been improved by using Polytetraflouroethylene (PTFE), for the composition of the crankshaft oil seal.
A longer life with better sealing quantities is claimed for the new seal. Longer life has also been given to the V engines' water pumps.
These are now using carbon which makes contact with a silicon carbide element in a steel housing to prevent leakage and protect the pump shaft and bearings from corrosion.
Oil consumption is improved on the V engines by more precise liner honing, and a closer matching of piston rings.
A stepped land piston is now used below the second ring of the three-ring pack. The liners themselves are further •protected by the use of a removable multi-purpose corrosion inhibitor. • To avoid the risk of oil leakage and contamination, a screw-on oil filter element is being used in place of the bolt-on type.
Oil circulation time when starting has been speeded up by fitting a larger diameter suction tube.
Cummins has modified its PT fuel pump, to eliminate the risk of air being drawn into the low-pressure fuel line via the tachometer drive take-off. The drive point is now located outside the pump body. New bushes and better sealing are also used on the throttle shaft.
To prove the design changes do work — and it's claimed engine life can reach 250,000 miles — Cummins has been showing two stripped down engines which have covered well over 200,000 miles.