Detergent Oils and Chromium Rings Double Engine Life
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DETERGENT oils and chromium-plated piston rings have extended cylinder life to double the pre-war length. Coupled with the larger bearing areas of modern engines of 9-10 litres, derated by 10-20 per cent. beloW maximum output, these developments have approximately doubled the mileage between overhauls.
These are some of the findings of a report, "Economies in Motorbus Maintenance," by a sub-committee of the motorbus committee of the Municipal Passenger Transport Association, released On Wednesday.
Under prevailing conditions of double-deckers, there was no major improvement in fuel economy compared with pre-war • experience. The substantial advance in overall weight had countered the increase in power, and only maximum engine output improved performance, says the report.
Progress was being made in reducing body weights. "With the advent of medium-weight power units a 121-percent. reduced weight of vehicle is a reasonable prediction. Modern versions of a 7-8-litre capacity engine under these loading conditions will not necessarily need to work to maximum capacity, and there is every indication that fuel-cost reduction will be appreciable," it is stated
Overcoming Abuse Epicyclie gearboxes were being used increasingly. Recent development of such units should limit abuse of changespeed bands and improve transmission characteristics. Extensive developments were likely with brakes, which accounted for the second highest single item of maintenance expenditure.
Supplement 1 oil extended cylinderbore wear by half and it was thus possible to lengthen the intervals between inspections. "In assessing economies of detergent oil it must be borne in mind that the straight oil can be filtered quite satisfactorily by an operator, whereas the additive oil would have to be returned to the manufacturers for refining and retreating," it is pointed out, More Evidence Needed There was insufficient evidence to prove that detergent oils improved crankshaft and bearing wear, and further experience was required with thin-shell bearings before they could be compared with the older thick-shell type. Slip-fit cylinder liners had given much trouble because of flange breakages and were often difficult to remove.
Hardened liners usually gave better wear, but their higher cost had to be considered, There was no advantage in using chromium-plated piston rings with hardened liners, but a chromiumplated top ring with a normal liner gave excellent results.
Detachable valve seats were satisfactory, but rocker-gear wear was excessive. Rocker pads should be initially hard-faced. An elaborate air cleanersilencer was not needed on vehicles with forward engines, and there was no evi
dence that • fuelconsumption was iffiproyed•by fitting an external cold-air induction system.
A 10-15. per. cent. reduction in idling speeds saved fuel, but many enginemounting systems were incapable of dealing with the vibration at such speeds.
The ordinary constant-mesh gearbox wore well and was easy to maintain. The synchromesh gearbox relieved the driver of gear-changing problems to an extent, but required more attention. Fuel consumption with the latest types was better than with a combination of fluid flywheel and preselective gearbox. . Chromium-plated king-pins, automatically lubricated, gave satisfactory life. Worm-and-nut steering systems appeared to wear better than others, but difficulty might be experienced in mating worm and nut after periods of running. Rubber spring shackles could cause difficulty in passing the tilt test.
Curing Brake Squeal There did not appear to be a universal cure for brake squeal, although drums fitted with liners were less prone to this defect. Moulded facings had a more stable coefficient of friction, but were more brittle than woven materials and caused heavy drum wear and heatcrazing.
Tyres with steel-wire casings lessened the incidence of punctures and could be remoulded four or five times. Remoulds could safely be used on front axles. Valve caps were too easily lost and should be made more captive.
The alkaline battery appeared to be a promising source of economy. P.V.C. insulation was recommended for starter cables, which could be more flexible. Semaphore direction indicators were costly to maintain, but further service experience was needed to determine whether the more reliable winking-light type was better.
FIRST TESTING CENTRE
THE first voluntary comprehensive vehicle-testing centre in this country is to be opened by Mr. Hugh Molspn, Joint Parliamentary Secretary to the Ministry of Transport, next Monday, at the Territorial Drill Hall, Uxbridge Road, Slough.
FUEL TAX CUT
AREDUCTION of 6d. a gallon in the tax on petrol and oil fuel was proposed by the Manx Chancellor of the Exchequer in the Isle of Man budget on Tuesday. '