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road and
Page 80
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workshop by Handyman
Details that save down-time (7)
Watch out for silencer trouble caused by idling in winter queues: hard carbon is best tackled by immersion in hot caustic soda
NOT all diesels can run for any length of time slowly and cleanly, and by slowly I mean at tick-over speeds, as one of the results of this is a steady build-up of either soft, greasy or hard carbon in the manifold fall pipe and silencer which can eventually cause overheating, back pressure and reduced performance. Certain short-stroke engines can even begin to let oil past the rings and deposit this in the exhaust system.
During cold weather long tick-over periods can be expected; in dockside and works queues a driver obviously has no wish to sit with his engine cold and his windows either steamed or iced up. Therefore you can gamble that even when instructed against idling their engines many will still keep their cabs at a reasonable temperature and screens clear so that they can move forward in their queues. When this is followed by a trip with plenty of open throttle, the engine usually cleans itself, often emitting a shower of sparks and soot from the tail pipe.
If, however, a vehicle is on local or town work and this idling occurs on most days, the exhaust system can begin to close up and not clear itself and the engine can go right off tune. I have seen some odd attempts made to clear choked up manifolds, including a young mechanic steadily tapping along manifold and fall pipe with a spanner. This risks cracking the cast iron manifold, and certainly achieves little more than dents in the steel fall pipe.
Where this choked-up condition is found to be severe the first task is to determine whether it is caused by hard carbon or a greasy deposit. Hard carbon is best tackled in the manifold by immersion in a bath of hot caustic soda solution. Arrange the mixture at about 3Ib soda per gall of water and soak for an hour or so to loosen off the hard carbon; for manifolds with tight bends or angles more time may be needed. The action will be faster and more thorough if the mixture is kept hot.
Protective clothing On removal from the bath the manifold should be thoroughly rinsed out with cold water. Remember, however, to wear protective clothing with boots and gloves, and that industrial goggles are an added safeguard against splash. A power-driven flexible wire brush can also help to clear the manifold ports. Most silencers are now of all-welded construction and cannot be opened; many are straight-through types with a slag wool-type packing around the centre passage or pipe. Holes through this pipe enable the exhaust not to be damped to a bearable level.
When the exhaust has to pass more oi smoke than usual these holes in the centre pip, steadily fill up — when they close up altogethe the noise level rises above the legal maximum Different methods have been tried out ti remove this clogging layer of carbon. One is ti fit several balls of steel wool on to a rope an pull this lot backwards and forwards severa times through the silencer and this can b effective if the carbon is not too hard. I hay heard of mechanics using a welding torch flam through the tube to burn off the oil coating an thus setting the slag or glass-wool packin alight. Nothing seems to put such a fire ou until the material is all burned up, and whe you finally shake out the debris all you nos have is a worthless item that is no longer silencer.
The best method is the hot caustic sod solution in the bath, and two or thre immersions may be needed in order to softe the carbon where it is through the holes in th tube. However, with the packed silencer an the use of caustic soda, some little time i needed to dry out the silencer and get the wate away from the inside of the shell; hot air wi help if available, but not flame. A good tins with cold water, then compressed air can b used with the silencer vertical. If the silencer i going straight on to the vehicle to operate, di drying out process will take care of itself — but do remember to give it that cold water rins after using the soda solution.
Next week in CM:
. . . a road test report on a new 16-ton vehicle fitted with a demountable body; it is described by Gibb Grace as "a vehicle with much potential in the door-to-door delivery field".
0 The Technical Editor is also dealing with that important, and often neglected subject, vehicle selection; and in Technitopics Paul Brockington takes another look at road tankers.
0 "Are your passengers sitting comfortably?" That's the question which Martin Hayes poses in an article which should be read by every psv man. 0 And European Scene takes its monthly look across the Channel.