ROAD AND WORKSHOP by Handyman
Page 39
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Tackling Bush-to-spindle Wear
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• WEAR IN ITS various foriris tends to fall into two categoriescritical, or just annoyinv but whether you clear up the problem in one swoop annually, or treat it as you meet .it, does mit alter its nuisance value. There is nothing more annoying to driver and engineer than parts that are worn and wobbly and for which there is no quick or simple cure. Some examples are: the hinge point of many handbrakes. control pedals and linkages of many kinds, and that evertroublesome second steering drop arm„ Most of these items are mounted on plain bushes with steel spindles and as wear becomes excessive so must the bush be Changed and the spindle built up and machined. There is a steadyround of this class of work in transport repair.
Taking the larger item, the second Steering drop arm: on many models this is a plain bronze bush on a steel shaft, Secured by either slotted nut and split pin, or split collar and pinch bolt In either case, it seems a short time only, from new or after overhaul, before the arm is free enough on. its shaft to give an impression of excessive wear, noted at the bottom of the arm when the steering is moved. So much so that during any Ministry inspection invariably this is one of the items listed for attentien; yet in actual measurernent, bush-to-shaft clearance rarely exceeds 0.015 in. • Also, this particular wear condition is not an amount of metal removed equally along one area of the bush, hut tends to be exaggerated at each end. Thus, attempts to stop the rocking movement Of the arm . by adding shims or packings usually make little difference; end play can be temOved, but the rocking motion is still here. .
.Although not in any way dangerous,
,ii , iS problem has such a nuisance value, particUlarly when no easy adjustment is possible, that: another method has been ' ried, not just on steering drop arms, but
. Ori several other semi-rotating items also. With the drop arm the first task is to countersink both sides of the hush area at the standard twist drill angle of 59°. Select for this job a drill of an oversize that will' countersink both the bush and the surrounding area of arm an equal amount by the time the drill has completely buried its cutting face.
TO simplify this operation, as the bush would be eccentric, it is advisable to press a hardwood plug firmly into the bush. mark off a correct centre, mount the item securely on the drill stand and feed down the drill lightly. We now-have a concave seating at both sides of the bushed item, and this seating registers equally in both bronze bush and steel arm. The fact that . the seating will be-part bronze and part steel will have little effect On the rate of ,wear. A pair. of cones are now required to replace the original rubber washers, and these can be machined in pairs from the one steel rod, but one of them should be bored out for an interference fit on the shaft inner end.
If the drop arm had been previously secured with a 'slotted nut and pin, this nut can be discarded in favour of a plain one, the outer cone now being welded to this nut and a second one obtained for a lock nut. On the model using the split collar and pinch bolt, it is necessary to dowel the cone to the collar to take up future wear. This method makes the steering drop arm adjustable' in a menu of minutes, compared with the earlier need to rebush and machine items that were not so worn as they appeared. The grease nipple is changed from the shaft end to the centre of the bush via the arm, and the close fit of the cones retain the grease satisfactorily.
West Country Winner '-"ri-flS week's prize-winner is Mr. P. G. I Mark, of Pinhoe. Exeter, Devon. When vehicles are regularly serviced by skilled staff trouble from U-bolts and centre bolts is rare, he says, as early warning of movement is given by broken dirt and rust streaks. An experienced fitter will rernove and free each nut and retighten, keeping an eye open when the vehicle comes in again and possibly retightening, preferably whilst the vehicle is loaded.
Accidents will happen, however, and it is not uncommon for movement to shear off the head of a centre bolt. These are sometimes quite a snug fit in the axle, or there may be a slight countersink or "lead " on the hole which becomes filled up with the burred head of the shearedoff bolt. Sometimes the axle platform is polished to the extent that it is quite
difficult to locate the filled-up hole. It can be located by tapping with 'a hammer and punch in the centre of the platform, depressing the stub slightly. The best method of dealing with this situation is to leave the wheels in place and chock them .well; after removing the slack U-bolts jack up the chassis and spring with care and patience (as near horizontal as possible) until a space is provided between axle and spring equal at least, to. the depth of the spring — this will usually provide working space. If the sheared-off head is really stuck it can usually he picked out with a dab of heavy grease. If it is tight the first step is to drill a pilot hole 0-25 in. right through it. If drilling has not freed it, grease again. Roll some water-pump grease into a pencil and insert in the pilot hole, tamp it down with a bolt until the space under the head is filled, cut a short length (about 1 in.) of 0-25 in. rod and insert into the hole. A smart blow with a heavy hammer will usually lift the head by hydraulic pressure This is worth trying, otherwise, it means that the stub is firm enough to he threaded; a bolt can then be screwed in to jack it out.
Put a lead on the new centre bolt and use it to gently tap the broken one out, lower jacks until centre bolt ,head rests beside its hole, then put the nut on and tighten carefully. The rest is easy.