OPINIONS FROM OTHERS.
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The Editor invites correspondence on ail subjects connected with the use of commercial motors; Letters should be en OM side of the paPer only and typewritten by preference. The right of abbreviation is reserved, and no respansibility for views
expressed is accepted.
The Inflation of Giant Pneumatic Tyres.
The Editor, TEE COMMERCIAL Moron, 124611 Sir,—The several letters Which have appeared In the "Opinions from Others" columns of The C OMmercial Motor in connection with the notes I sent you on my experience with pneumatic tyres are undoubtedly interesting and informative, and they are bound to be appreciated by the people interested in this very vital subject. An operator of a large fleet of omnibuses cannot to-day indulge in personal fancies, for the balancestet is so very largely concerned with •low running costs.
The information I sent you is based on my experience as a practical operator of omnibuses and not as a manufacturer of air compressers. The great disadvantage of the small air compressor fixed to the chassis and driven from the gearbox is that, whenever air pressure is required from that compressor the engine has to be started up and run. Only those people who have started up hea,vy motorbus engines, with Carburetters set very finely, during cold weather, know the difficulty one has to gel a cold engine to run steadily enough at slow speeds to carry out the work of operating the air compressor. In addition, most of these compressors are fitted behind the gearbox, and in cold weather the cold gearbox oil has also to be churned up. * I think my brother operators will agree with me on this point; and, furthermore, without an air bottle working at 1,800 lb. per .sq. in., or a low-pressure cylinder working at about 350 lb. per sq. in., it is not possible In larger garages to carry out testing and " topping-up " of tyres during the night by the night staff. I am convinced that whatever method is finally adopted for maintaining the air pressure in the tyres of a. fleet of buses, there must be some portable facility for quick topping-up of tyres which have lost air pressure during the day. Again, there must be some reserve compressed air supply available whereby a number of tyres may be quickly inflated in garages where there is a big fleet of vehicles. • I myself am still examining and following up the different methods which are coming on the market for providing compressed air supplies, such as the portable electrically driven pump, the portable electrically driven pump and air tank, the low compression air tank charged from a central fixed compressor, the provision of air supply lines from a central compressor and similar ideas.
In conclusion, let me say that I pointed out several times in my article that the opinions expressed were personal opinions, based on hard-running experience, and I have not yet seen, heard or tried out any apparatus which has to-day altered those views.—Yours f al thfullY, L. G. *W/NDITAM SHIRE, Chief 'Engineer.
BIRMINGHAM AND. MIDLAND MOTOR OMNIECS CO., LTD. Smethwick, Staffs.
Warning Lights on Cycles.
The Editor, THE COMMERCIAL MOTOR.
124621 Sir,—On the Continent, in France in particular, cyclists carry a small folding candle lantern that gives them a light ahead and shows to all overtaking traffic a good red light, thus safeguarding themselves from possible accidents, which might result in loss of life.
These small lanterns are made of cloth, and fold similarly to a pocket-book. We understand they can he bought for 2s. fid. As they are so cheap and satisfactory, is it too much to ask all cyclists who are on the road at night to have such a light. They would thus greatly assist in making the road safe.—Yours faithfully, LIME STREET GARAGES (LIVERPOOL), LTD.
Th3 Correct Grinding of Cylinder Bores.
The Editor, THE COMMERCIAL MOTOR, [24631 Sir,—The device shown by " W.A.S.W." on page 89 of the issue The Commercial Motor of the 2nd inst. is quite good: I often hear of wear of cylinders lately and reflect on the factthat many 1905-1909 Talbots are still running with their original pistons, cylinders and valves. Now, all the new cylinders of that period were lapped somewhat spirally—almost vertically. An overhead countershaft had a disc and Ml
crank pin, and the cylinders were slowly revolved under the reciprocating lapping piston.
Cylinders are often ground, but all grinding for reciprocating motion should be lapped or polished lengthwise after the first grinding; this refers to pistons, valve stems, etc. In this connection all sewingmachine needle bars are finished lengthwise ; they are never ground circularly, Q.E.D.—Yours faithfully, C. R. GARRARD. Winchester Ball Bearing Works, Sydenham.
The Editor, THE COMMERCIAL MOTOR.
[2464] Sir,—In the issue of The Commercial Motor for January 19th there was published on page 795 a contribution to your columns of "Useful Ideas for Lathe Operators" from "R.H.," of Trowbridge.
A few years ago the method of repair therein described would have been the only practical alternative to a new screw, but when It is remembered that the worn thread is not only distorted and out of pitch, but of varying thickness of thread, it is plain to see that
when the misshapen thread is " run in" as described, with sand, etc., there must still remain considerable play or backlash, at the points where the thin threads engage the thread in the nut.
; Therefore, it is at best a very unsatisfactory repair. If the worn thread, is built up by the cold process known as the Fescol process, whereby pure nickel is deposited of sufficient depth to allow, the thread to be recut to standard original size, the resultant job will be a thoroughly mechanical one, providing a thread which, in addition • to giving considerably longer 'wear than in the first instance, will be perfectly rustless, a useful feature on lathe work where water for cooling purposes is so often used.
After such rebuilding, the thread is accurately recut, thus being of correct formation and pitch and a 'good fit to the nut for its whole length.
We should much appreciate mention of this in your columns, as the tip may prove of service to your many readers in the future.—Yours faithfully,
London. FESCOL, LTD.