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THE ILLS WHEELS

10th September 1943
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Page 26, 10th September 1943 — THE ILLS WHEELS
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Which of the following most accurately describes the problem?

Although Comparatively. Rare, Wheel Troubles are Likely to Increase Owing to the Greatly Extended VehicleMileages and the Difficulty Attendant

Upon Renewal Following an Investigation by This Journal, We Are Now Able to Give Much Useful Advice to Operators From Wheel Makers in Respect of Inspection and Maintenance

AT the request of the leacling tyre makers of this country, and with most satisfactory co-operation

from vehicle-wheel manufacturers, " The Commercial Motor " has conducted an investigation into the troubles Which may occur with wheels, particularly those used on the heavier classes of goods and passenger vehicles, what should be looked for, and how breakdown and accident may be avoided.

In the course of our inquiries, we visited the works of the following four wheel makers:—Dunlop Rim and Wheel Co., Ltd.; Kelsey-Hayes . Wheel Co., Ltd.; Joseph Sankey-and Sons, Ltd.; and Steel Stampings, Ltd.; also, we made contact with the Technical Branch of the Society of Motor Manufacturers and Traders, to all of which we would like, at this point, to express our appreciation of their willing collaboration We would emphasize that, so far, the faults occurring in wheels, whilst they may be serious in individual P. cases, are not widespread—in fact, it is estimated that failures take place at the rate of only about one in 10,000 wheels. The chief cause is, apparently, fatigue resulting from operating vehiaes for much greater mileages owing to the difficulty of replacement. This must necessarily be combined with the exceptional conditions of usage due to the war, such as heavier loading, reduced or less-expert maintenance and, sometimes,the changing-over of wheels from old vehicles to newer ones. Hitherto, wheels have given so little trouble that they are now apt to be neglected, attention being concentrated upon tyres.

-Few' people realize the variety and extent of the stresses thrown ',upon the wheels of a vehicle. There is, primarily, the vertical loading, but more important is the. " rocking stress set up when a vehicle is cornering at speed. Then there is the force thrown on each flange of the rim by the pressure. within the tyre, and this is accentuated on the inner flange when a wheel, particularly at the near-side front, is forced against the kerb.

There is often a concentration of stresses at some

point between the nave and the rim due to inherent differences in design. The wheel maker cannot always have his own way in this matter. He has to allow for the requirements of the vehicle designer in respect of brake drums, etc., and whilst he may do his best to distribute the 'strength so that it will bear a true relationship to the stresses, this cannot always be

achieved. .

In addition, work-hardening of the material may occur at certgin points during stamping and punching, and thus reduce the capacity for deformation in some ' areas. Also, at some points, such as the riihs, the bends must necessarily be of small radii.

However, some of these problems, as well as others, are discussed in the comments made by the authorities . mentioned. These views from the wheel rnakers are, purposely, not given in the same order as their names.' but there is surprisingly little variation between them

Wheel Maintenance and Insliection are Vital

T0 avoid wheel failures which mEw result in tyre damage and other losses, it is suggested that there should be a routine inspection of the wheels on all commercial vehicles. This might well be on the following lines, with . possible modifications to.. suit special cases. DAILY.—Test the wheel nutS for tightness. WE.F-KLY.—Make a close scrutiny of each wheel as it stands on the vehicle, to detect any signs of cracks. MotiTin,y.—,Remove each wheel from the vehicle, for a more thorough examination than the weekly one, which will permit examination of the hubs, and hub studs at the same time. QUARTERLY.—Remove the tyres from the wheels for a very careful examination. In the case of used stock in the operator's pbssession, the inspection should be similar to that of the quarterly examination. As this may be an important factor, all old wheels already in stock might well be submitted for such examination at once, so that they shall be immediately

available for use. . •

• By way of guidance for the routine inspection, the following notes should be helpful:— Elongation of the stud hole, is usuall§ easy to detect and it constitutes a serioul.fault, Commonly it is caused by wheel nuts not being thoroughly tight, but it ca.n arise also from other causes. The studs themselves May be loose in the hubs, so that even when the nuts are tight some movement. occuts between wheel and hub. Again, if dirt or grit he present between wheel and hub when the

nuts are tightened, this foreign matter is likely to crush or spread later, so that the wheel becomes loose 'on its mounting In the case of twin wheels, the inner one seats on conical shoulders in the studs, and it is not unknown for wear and elongation to occur there, even when the miter stud holes are not damaged. The inner holes, therefore, must be examined carefully every month.

A further common wheel fault is due to the possibility that careless removal of the spring ring may have overstrained it. When installed on the wheel there should. be only a small gap between the two ends of this ring, which retains the loose flange. In its free position, whtal removed from the rim, the two ends should definitely overlap. During removal of this ring, no attempt should be made to " peel " it off, So to speak, over the whole circumference of the gutter simultaneously.. Commencing at one end of the gap it must he levered gently out of its' channel

all the way round until it comes freely away. This process is not ctifficult and 'it will avoid overstraining the ring, tfut when a ring has been strained to that it does not contract properly into its channel it should be returned to its maker for resetting or replacement 'as necessary: Apart from the commoner faults so far described, and which are largely capable of avoidance by normal maintenance, there is a further class of failure which has occasionally been encountered on 'wheels which are known to have been in arduous service over an extended period of rime. This takes the form of cracks in the disc or in the rim. The former usually occur from a stud hole to a nearby lightening hole, but sotnetirnes can appear between two adjacent boltholes or lightening holes. In general, such cracks will show through the paint practically " as soon as they form in -the metal. Provided the wheel be clean, detection is not difficult.. Frequently, too, they can be detected as a slight but distinct tap for every , revolution of the wheel, this being caused by the impact of the two surfaces of the crack when that part of the wheel comes under load.

Another point at which a crack may develop is at the depression formed in the circumference of the disc to accommodate the tyre valve. This, too, is usually easy to see and, unlike most other, wheel faults, it can be cured by careful welding.

In the rim itself, any tendency towards cracking is usually confined to the root of the fixed flange. This may be caused by incorrect inflation pressure (under-inflation as Well a.s Over-inflation), by the fitting of a wrong size•of tyre or by over-loading, but in the unlikely event of its occurring, despite all other factors being correct, it may start as one or more corrosion spots from which hair cracks develop. At that stage it is exceedingly difficult to detect without special equipment.

These hair cracks later join up to form a larger crack which may result in complete failure of the rirrY. Cracks of this kind, when they occur, are almost always in 'the inside of the, rim and therefore they can .be detected only when the tyre is removed. Tapping with a hammer is 'not found to provide satisfactory indication of the presence of a crack.

Commonly, the crack is concealed by dirt or rust and any attempt to rub this off usually makes the fault still more difficult to see. The rim should therefore be examined first as it is when. the tyre is removed, perhaps using a magnifying glass as an* aid, Possibly the thorough uSe of a wire brush might then be tried and it has been suggested that a small crack might be shown up by smearing the area with thin oil and, after an interval, wiping it as clean as possible. Oil contained in the crack might then exude and show up the fault, but it must be emphasized that this is by no means a certain test.

A much surer way is to shot-blast.or sand-blast the rim and then to examine it with a good magnifier. In the maker's laboratory the shot-blylwn surface would be etched and then inspected by microscope, hut this process is probably outside the scope of the normal operator.

Fortunately, it is true that these rim cracks usually take sonic time to pass threttgh the various stages of development. Admittedly, even in the, early stages, the rim loses some of its strength and might fail in an emergency, but generally it does not become dangerous until the crack is large enough to be seen under careful inspection on .the lines suggested in the preceding paragraph, and the examination is therefore well worth making.

. Where Particular Attention is Needed

ONE of the most important points is that vehiclernaintenance engineers should make sure that wheels are thoroughly examined when the tyres are changed! Particular attention should be paid to the following points:—

The eirrts should be checked for flaws or tracks, and any rivets examined to see if they be tight. The gutter into Which the spring ring fits rhay be distorted or broken, and the ring itself may be distorted or strained. Examination should also be made of the nave, to see that the 'spherical ' nuts can seat properly and that there is nn ilongation of

the holes. The ,latter feature' alone is -proof of some cdovement. This elongation means that the spherical nuts cannot possibly fit properly and have their correct area of contact, so that tightness is not ensured.

In some wheels, the nave is made slightly concave in preference to being flat, so that when twin wheels are together the two naves act as a spring. In any case, the

faces should be perfectly clean; any dirt picked up, say,•by laying the wheel in the road, particularly on tar

macadam, may result in grit being picked up. This may also prevent the spherical nuts from seating truly. It is important to remember that if one wheel of a pair becomes cracked, the other will take the bulk of the load, as the defective wheel will give. In any case, owing to road camber, the inner wheel nearly always takes the • bigger share.

It is also important that twin tyres should have equal pressure.Some authorities recommend that the outer tyre should be slightly harder, but any difference is apt to encourage mistakes.

We are not' greatly in favour of the welding of wheels as a general practice, as this requires proper equipment and really expert attention. Vor instance, in the case of any weld near the bolt holes, correct machining is essential. It is, however, possible, in the initial stages, to arrest the progress of a very short crack stretching, say, from a hand hole towards a bolt hole, in which case the crack should be cut into a '" V," welded and dressed.

Creaking of a wheel when'the vehicle is running with the engine switched off is ,almost a sure indication of trouble; likewise, if a wheel be covered with mud except for a clear space, movement in it is indicated.

Red 'dust around rivets, or clean spaces in the same positions, often show movement.

Cracks sometimes occur in the rim between the end of the slot or depression for the valve stem, towards the fixed flafige. In wheel centres, cracks are usually between the bolt holes.

Some types of wheel are fitted with what is generally known as four-piece rims. With this type, in place of the usual fixed flange a loose one is slipped on and abuts against the raised edge of the rim proper. Eiy virtue Of its heavier „construction it seldom gives trouble..

This particular maker carries out very drastic tests to ensure that wheels are up to standard and capable of carrying the required loads. One of these tests. is to damp the wheel rigidly by the tyre or rim, a stout bar is then fitted into the hub, the other end of this bar being weighted; thus, when the wheel is revolved, alternating stress is thrown upon .it.

. No, new type or design of wheel-is allowed to go into production until it has withstood a predetermined number of revolutions with a given load; in most cases this is in the region of 200,000 revolutions, whereas a defective wheel may fail at 50,000.

Hardness of the materials is also tested at different points; likewise 'measurements for thickness of section.

.Be Suspicious of Any Old Wheels

THERE is a widespread belief that a wheel will last for I ever, but it will not. This point was emphasized by one important concern; which deprecated the practice of bringing. any old wheel back into service without a thorough inspection. There are two 'particular parts of a wheel which call especially for examination before it is -entrusted with a further spell of duty. . In this connection it must be mentioned that the number of wheel failures is very small indeed when compared with the number pf wheels in use—it has been estimated as about one in 10,00,0—but any such failure may result in foss of life and almost invariably it will cause a waste both of vehicle hours and of precious tyre rubber. No reasonable precautions should be omitted to avoid these possibilities. Apparently only individual care can guard against the use of faulty old wheels already in the possession of operators or obtainable from the numerous breakers' yards all over the country. , Of the two features alling particularly for inspection, _one is casy, to examine. Stud holes in old wheels often are elongated as a result of the retaining nuts not being tightened sufficiently. [1'his deformation of the metal is liable to start cracks, which may result in failure of the wheel. Apart from that, the wheel cannot be held firmly when the 'holes are in this condition, because the nuts cannbt seat properly.

Ow-some wheels returned to this maker it has been noted occasionally that attempts have been made to build up elongated holes by welding, but apparently this. rarely makes a satisfactory job. It -is sometimes possible for the manufacturer to fit a new disc to the original rim of a riveted-type wheel it that be in good condition, although even this repair. is .not one which this company ,views with complete approval, from technical considerations concerned with the riveting.

In the rim itself, long and arduous use is apt to start a crack at the met of the fixed flange. This is, in effect, a fatigue failure. It -can be detected sometimes by visual examination. An alternative and probably more searching test is to tap the wheel with -a hammer—much as railway wheels are, tested regularly. A cracked run emits a sound which is quite different from that of an undamaged one. [Other makers do not place much reliance upon this test....

ED.] .• P°

. This fault is caused, of course, by the lateral forces acting on the flange, both when cornering and when the normal load on the tyre squeezes its walls outwards. In the experience of this concern, the fitting of oversize tyres increases these lateral forces and is likely to cause such failures.

It has been noticed, too, that the near-side front wheel, 'particularly on public-service vehicles, is especially liable to develop a crack at the flange root. This is attributed to a tendency on the part of drivers to stop with that wheel against the kerb, a result being that the lateral forces are reversed and probably increased considerably at the same time.

-In view of the variety of conditions under which a wheel can operate, obviously• it is not possible to state its probable life in terms of miles. Some wheels can and do outlast the vehicle they carry. Others, equally strong, but subject

to more arduous work, cannot. Especially, now that vehicles are being retained in service at a greater age than usual, is 'it necessaryto remember that wheels, like most other chassis parts, may need replacement. The rule, therefore, should be to examine every wheel carefully before a new or reconditioned tyre -is fitted to it, and to be particularly suspieions of any old wheel which it is proposed to put back into service.

Problems Mainly Effect of WarConditions • rIF necessity, vehicles are being kept running-far beyond is–/their estimated economic mileage, and the conditions under which wheels, are now operating are particularly _severe. Refearing particularly to public-service vehicles, these are now carrying far greater loads than they' did in pre-war. days. The conditions of roads have deteriorated somewhat, and skilled maintenance ambinspection have not been kept up to-pro-war Standards.

However, despite these abnormal conditions, 'with which all operators are familiar, wheels generally have been proved to be very satisfactory and little trouble has been experienced with them. The number of wheels which has been replaced for any reason whatever is very small, but any failure of a wheel may be the cause •of -premature failure of the tyre or other serious damage to the vehicle or components. In the interests of public safety and in Order to conserve rubber the Wheel manufacturers consider that they cannot emphasize too strongly the need for operators to enlarge and intensify their wheel-maintenaace systems. With this thought in mind, it is considered necessary that the following actions should be taken:— (1) Check studs and nuts, which .secure the wheels to the hubs, daily, for tightness of assembly. Note:—Make sure that the wheel is tightly-'gripped by the nose of the nut. It has been found in some cases that, although the wheel has been apparently tightly secured to the hub, owing to excessive wear of the bolt holes and the nose portions of nuts, the nuts have been binding on the shoulders of the studs before tightly gripping the wheel; a typical example is shown in an accompanying illustration. (2) If the bolt h6les of wheels show signs of excessive wear or elongation of the bolt boles, check studs for tightness ht hub, replace with new wheel and ensure that the wheels be fitted tightly to the hubs. If the nose portions of thenuts be worn badly, also replace these.. (3) Check tyres for pressure at regular periods, as recom .

mended by their makers. It is important that they should not be appreciably more or less than the standard pressures quoted.

(4) Examine wheel discs weekly to make certain that r o cracks have started to develop. Usually such cracks are found to develop from one bolt pole to another, or from one bolt 'hole to a lightening hole, or along the depression in vihich the tyre valve seats Generally these cracks develop. some time previously to complete failure, and • regular inspection should, therefore, eliminate the possibility of failure on the road.

" (5) At monthly intervals each wheel should be dismounted from its hub, the tyre removed and the wheel thoroughly cleaned . down A -very close examination of the/inside-of the rim, near the fixed Ilange, should be made to ensure that no cracks have begun. to develop. These cracks usually occur circumferentially around the rim, and if not detected will result in the complete destruction of the inner tube, also, possibly, the cover of the tyre.

(6) Keep wheels free from dirt and rust.

It should here be noted that, from the safety aspect, it is important to give a more careful inspection to the .front wheels than to those at -the rear. It Will be realized that failure of a rear wheel (particularly when twin wheels are fitted at thern rear of the vehicle), whilst, possibly, causing other mechanical troubles, is not so dangerous, for the reason that the'steering is not affected. The following general remarks which may refer to all types of wheel are .worthy of note:—

Spring flanges or lock rings: These are the spring rings which fit into grooves and retain the tyre in position on

the rim. To remove these they must becarefully levered over the. edge of the groove inch by inch to avoid distortion. When removed the ends of these spring rings should

overlap. Should this not be the case, they should be immediately replaced by new ones. When correctly fitted in the groove of the rim of the wheel a small gap should be apparent between the ends of this ring. Do not Lit any spring flange or locking ring from which an end hai been broken On some makes of vehicle it will be found that the wheel. hub stud and securing nut are made from two or more parts. Care should be taken to ensure that these parts be assembled correctly, and that if any of these parts be lost the vehicle shall not be operated until new fittings are assembled

Finally., this maker considers that if the foregoing sug. gestions be carried out they• will have a considerable bearing on the satisfactory operation of the wheels. Thr . company does not recommend that any wheels which are badly damaged, cracked or which have stud holes badly worn, should be repaired by welding or other methods, but such wheels should be replaced immediately by new ones.

If and when new wheels be required the maker would welcome, in addition to the usual details to enable them to supply, any information which can be given of the conditions under which the wheels are to operate, e.g., the gross load of the vehicle without passengers (or load), the number of passengers (or weight of load) carried at peak periods, and the pressures to which the tyres.(size of which should be stated) are inflated.

In connection with this last point, --a further important factor is whether the combination of rim size of wheel and tyre size is in accordance with the S.M.M.T, Recommended Standards. If this be not 'so, the possibility of changing the size of rim in order to bring about that

condition is recommended. .


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