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Mischief on the Motorways
Page 81
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BY HANDYMAN INa past Wide some of the benefits arising from our new motorways were discussed, and it would appear that engineers are in for an easier time. However, just as certain old features of mechanical bother have disappeared, so have new ones come along and need to be appreciated. One of these is the effect of vibration from continued full-throttle operation, and in certain instances the results are quite shattering.
With a large fleet it is a little easier to measure effects and thereby separate the odd incident from the regular feature. Thus some steps can be taken to counteract any recurring mechanical expense.
Prominent amongst the defects arising from motorway operation is the frequent one of loosened companion flange bolts, together with occasions where the flange-topinion-shaft nut has eased off also. On certain vehicles this is first noticed when
the differential becomes noisy, and. a close inspection is called for. Then it is found that the splitpin is sheared and the nut has slackened off, permitting the load to come off the inner cone of the outer bearing. If this remains undetected, the pinion-bearinghousing studs can ease back, followed by the pinion starting to move out of mesh.
After several instances of this trouble in various stages, closer attention was paid to the prop-shaft itself, and on four occasions this was found to be either bent or out of balance. On another model where a damper is fitted, the damper linings can wear eccentric and bring on an out-of-balance condition that will worsen rapidly if not detected.
From these motorway vibration defects there arose the need to lay on a closer inspection of all long prop-shaft models by jacking up and running in gear. One cause of the bent prop-shaft is, unfortunately, laid at the door of the repair shop. This can occur when the gearbox is removed and the vehicle pushed aside by hand to park or wash down. Then, unless the long shaft has been removed or carefully lashed in a central position, it can thrash around when the vehicle is man-handled and can be shocked on the chassis side and distorted; very little distortion is needed to produce vibration at maximum r.p.m.
A further series of events with valve and piston trouble drew attention to air cleaners, particularly the horizontal dry filter, and following upon several bent valves, damaged
seats and bruised pistons, the fault was located in the air cleaner. Parts of the vanes or framing had fractured and disappeared down the airtake and in all instances the air cleaner was dancing and loose within its clamps or brackets, or the fixing studs had gone altogether.
Joindess valve covers are frequently loose, and on five vehicles where the air tank is suspended on welded brackets, these had parted at the weld, calling for a modification to incorporate straps instead.
It is now clear that trunk operation over motorways is going to produce more and more of these problems. For those vehicles so engaged the only answer is a rigid, short-period inspection not exceeding fortnightly intervals, paying special attention to the points described above.