TRIMMING WORN JOURNALS.
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ONE OF THE difficulties which is met with during the repair or overhaul of motor vehicles, and particularly in the case of crankshafts, is ovality of the journals. In course ef time a crankshaft, however true it may have been at the commencement, wears out of bale owing
to the u i unequal pressures to which it s subjected whilst in service.
When the ovality is beyond a few thousandths of an inch it is useless wasting time in fitting new bearings to the journals, as they will never give eatisfaetion for any length of time. If they are fitted te the " narrow" side of the oval journal they will., be too -tight on the ' broad," and if hey are fitted to the "broad " they will be too slack on the
" narrow." In 'addition the journals often wear unequally in the longitudinal direction and sometimes score.
In small repair shops it has been the custom to file the journal approximately round and then to lap it with either a lead lap and emery or carboninduan powder, or by means of emery tape, in which case the tape is wound once round the journal and the ends given an upand-down and sideways, movement, so that the tape travels from end to end of the_ journal whilst rotating.
This 'tether] is not very satisfactory and requires considerable labour. An alternative method is to turn down the journal in a lathe, but in the case of large crankrhafts lathes sufficiently large are not always available and the jourual face is often so hard that it is difficult to skim the surface. Grihding the journals is perhaps the hest method of all, but requires the use of an expensive -machine tool.
An interesting little device has rrcently been brought, to our notice ; it is known as the Porerl crank-haft grinder, though grindrr " is somewhat of a misnomer, as it is more of a cutter than a grinder. The instrument consists of an aluminium casting split into two halves and hinged at one end. The halves are not quite equal, because one half acts as a handle, to which the other half is bolted.
The drawing which we reproduce shows how the cutters are positioned. • The holder for each cutter has a circular shank, which passes threugh a hole leading from the inner periphery of the casting to the outer. At the outer end of the shank is fixed. a key, which is free to travel in slots cut in the hole in the casting, thus preventing the shank from turning. Skew teeth are cut on one side of the shank, and these engage with the face threads of an adjusting ring. This adjusting ring is also splitem two halves SO that it can be opened with the two halves of the casting without interfering with the adjustment. The adjusting ring is providrd with two holes, in which a special spanner provided with the device engages. Incidentally, to lengthen the life of the adjusting ring it is strongly made in la.onze. The cutters are Made of tool steal.
The cutter can be used on journals from 121; in. diameter up to 24 ms. diameter, and is intended to be operated by hand. To use the tool, the adjusting ring is turned dntil the entting edges are separated by rather more than the diameter of the journal to be cut. The tool is than opened and slid over the journal, after which it is closed and the two halves held together by the nut and bolt provided. The adjusting ring is then turned in the reverse direction until the cutters press against the journal.
After taking a cut over the journal, the cutting edges are again closed in arid further cuts taken until the journal is perfectly trne It will be readily understood that a 'tool of this description is an invaluable adjunct to any small enginereing shop not well provided with machine tools.
The cutters can be easily replaced at a small cost, but they are capable of being ground several times before this replacemerit is necessary. The device is sold complete with a special shaped spanner for turning the adjusting ring.
The price of this little tool is £15, and it can be obtained from T. B Andre and Co., Ltd., 5, Daring Street, New Bond Street, London, W. 1. This company can also give quick delivery of the well-known Wisconsin rear axles, which are said to be the best constructed worm-driven axles in the U.S.A.
The worm gearing and differential form a unit with the axle cover and can be readily removed to facilitate inspection or repair.