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Silencers: prevent
Page 44
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failures save brass
TWO OF the surest ways to attract the attention of the transport antagonists are to allow your vehicle to be either noisy or emit excessive volumes of black smoke.
The first of these sins is caused most often by thoughtless handling but also by failure of the vehicle's silencing system. The second can only be caused by faulty equipment of one sort of another or misuse of the cold-start excess fuel device.
Whatever the cause, however, both failures to endear the vehicle to the general public cost you, the operator, money as well as reputation and should never be allowed to persist for any period of time. Eventually, of course, either fault will inevitably attract the arm of the law with a GV9 as the end result, issued either on an immediate or delayed basis and duly logged on your operator's licence.
In many cases the failure of the vehicle's silencer can be attributed to the lack of attention to the bracketry of the exhaust system as a whole. How often do we see vehicles on the road with half the system waggling about, just simply relying on the strength of the exhaust pipe to hold it up? And remember that the effective weight of the system hanging on only by the manifold flang, is multiplied many times over by the mechanical advantage of the length of the pipe, times the weight of the assembly divided by the dimension of the manifold flange.
Stresses
Then the stresses that are applied to the manifold are not only in one plane but in every conceivable plane, placing all sorts of stresses on the casting for which it was not designed. The end results are most usually loosening of the manifold flange or cracking of the pipe at the point of the highest bending moment, but quite often there is also substantial damage to the manifold itself, through cracking or continuing blow-by of the exhaust gases which eventually destroy the accuracy of the mating faces and so make it impossible to retain a gas-tight joint.
Preventive maintenance is, we all know very well, an essential item in the upkeep of a vehicle. In many companies, however, this is restricted to the engine and other major units which, records show, do not account for the majority of unscheduled failures_ The keeping of a history sheet which highlights not only the failure which causes a vehicle to break down, but also the reason behind that failure, can prove to be a very enlightening document. And with no shadow of a doubt it will add to the activities of your preventive maintenance programme and become an essential part of your future planning of vehicle specification.
On my own vehicle, for instance, I found that at 86,000 miles approximately, the front bulkhead of the silencer cracked around the input pipe.I noticed it soon enough for a satisfactory welding repair to be carried out. But within a further 4,500 miles the crack appeared again, but this time it ran into the body of the unit.
Tests
I repaired it a second time and when it was refitted, ran a series of tests at varying engine revs to ascertain how the assembly behaved. At 500 rpm and over, the whole unit kept practically still, but when the engine revolutions were momentarily pulled down below the 500 mark — when engaging the clutch for instance — the whole lot danced up and down between the silencer mount and the manifold flange, putting the forward bulkhead of the silencer into a severe state of flex. The solution was to fi metalastic-type mounting on the exhaust pipe just in from the silencer (Figure 1) to act steady. The cost of the corn p1 repair which has now remair intact for over 100,000 mil was £18.80.
The cost of a replacemi silencer would have been E6-, the time and I think I could N looked forward to a similar f ure at around 170,000 mi That silencer today has a price of El 12, and it is proba not of as good quality as • original unit.
A little time spent think about why something happi can often prevent the same f ure occurring a second time C save quite a bit of brass at same time.