OPINIONS FROM OTHERS.
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The Editor invites eorreepandence on all subjects connected with the use of commercial motors. Lette's should be on one side ot the pafier only and typewritten, by preference. The right of abbreviation is reserved, and no responsibility „tor views
expressed is accepted.
Big-ends and Their Troubles.
The Editor, THE COMMERCIAL MOTOR.
[2,650] Sir,—With reference to the page in the issue of The Commercial Motor for December 6111 on ends and their Troubles" I notice that not one of your contributors has mentioned the fact that failure is sometimes due to bad fitting.
If a big-end be fitted very tight the white metal tends to spread outwards to the side of the bearing and, to allow for this, sufficient clearance must be left on the radius.
Those of your contributors who have had experience of "burning in" machines no doubt will have noticed the plastic metal trying to squeeze its way out of the side of the bearing.
_Another fault in fitting bearings—and one which isall too common—is that the crankpin and the bearing are both well oiled prior to tightening up the cap. This is obviously wrong, as, in a case when a bearing is fitted with a number of shims, all surfaces of these become coated with a film of oil and when the big-end bolts are tightened up this film is not totally expelled. The best method, of course, to obviate this is to assemble the bearing dry, or, if this be impracticable, a small amount of oil should be put on the crown of the bearing only before assembling.
The sole point your contributors seem to raise is that the bearing should be left to stand slightly proud of its keep. This, of course, is, or should be, clearly understood bi even the average mechanic. Another fairly common cause of failure In a big-end is the use of an oil having too high a viscosity. It is a peculiar thing that this is not generally recognized. Some users appear to think that if the oil film breaks the viscosity of their oil is too low, whereas, generally speaking, it is the reverse.
I think the trouble is that users fail to grasp the fact that the oil Man does not roll over the. metal, but adheres to the metal and .rolls over itself, and at high speeds, if the oil be of too high a viscosity, the film is liable to rupture.
In the above stateraent on lubrication I have, of course, not taken into consideration the question of pressure on the bearing. .
Other and more generally acknowledged causes Of failures of big-ends are mal-aligninent of the connecting rod ; the neglect to mark the bearing § correctly when fitting (this is fatal in the case of a taper crankpin), and the fitting of bearings to an oval shaft. This is very often done with the idea that, provided the bearing is reasonably tight, everything will be all right, but so long as users continue the practice their big-ends will always be punching out.—Yours faithfully, London. JAMES EESKINE-SHAW.
The Problem of the Wheel Arch in Buses.
The Editor, THE COMMERCIAL Moron.
[2,6511 Sir,—As an owner of a number of motor coaches and buses, I was interested in the articles which appeared in Ties Commercial Motor concerning bodywork and the ideas of bodybuilders for the new vehicles that are coming on the road.
There is one point in your articleswhich induces me to write to you, and this refers 6) the problem regarding the wheel arch and its effect upon seating accommodation, which seems to be of concern for the coachbuilder. My contention is that too much is made of the intrusion of the wheel arch into the body space, and that the passengers do not consider this intrusion so serious as do the,goachbuilders and the coach owners:
We all of us like to rest our feet. At home we put them on the fender ; at the kinema people put their feet on the seats in front of,them, and children will always rest their feet onethe staves of Chairs.
After a lot of discussion I recently got a local coachbuilder to make for me a motor coach with the seats 229
only 9 ins. high. The only real defect was that parcels could not be placed under the seats, whilst the outlook from the windowS was lower, but the seats were very comfortable in which to sit.
I think that body designers must be very tall men and that they plan the seats to suit themselves. The average height above the floor level is 14 ins. or 15 ins., but if a small elderly lady be asked to sit in a seat of that height her feet will then he off the ground. The weight of the legs should not be allowed to come on to the Inside of the thighs, its the flow of the blood is thereby restricted. My experience of coach and bus operation is that lady passengers especially like to sit In the seats over the wheel arches because then they can rest their feet upon the wheel-easing arch.
My latest idea is to equip every seat with a plated rail underneath, upon which the passenger behind may rest his feet and thus obtain more comfort. Easy chairs are made low, and in public-service vehicles the comfort from this low Seating can he obtained by raising the feet in the Manner I have recently adoptect—Yours
faithfully, C. W. HUNT. Hawkinge,-Kent.
Fabric-lined versus All-metal Brakes.
The Editor, THE COMMERCIAL MOTOR.
[2,6,2] Sir,—Being careful and interested readers of your journal, we have not failed to note the letters from certain of your correspondents on the subject of metal brake lining and refer in particular to the letter from Mr. A. W. Seagrief in the issue of The Commercial Motor for October 11th.
To the uninitiated it may appear that metal brake linings are something In the nature of a novelty. In this regard we may remark that probably every individual manufacturer of motor vehicles has thoroughly tried out metal, the net result being overwhelmingly in favour of aS6estos-fabric lining. Discussing the matter with a member of a firm which specializes in the conversion of all metal to fabric-lined brake shoes, the peal-.
tion was summed up neatly in the remark : "The more people who adopt all-metal brake shoes the better it will be for our business."
We believe we are correct in stating that in no business is greater attention given to working efficiency, safety, detail expenditure, or greater keenness exhibited in reducing costs, than in the industry of passenger ransportation, and if any advantage, however small, in ervice or cost were forthcoming from the use of allmetal brake shoes, the interests of the brake-lining rade would be affected seriously ; but what do we find?
After exhaustive trials, asbestos-fabric lining of the best quality has proved—incontestably proved— superior to metal in all essential requirements. Hence, it has practically eliminated metal and has become, with few exceptions, the standard fitment for brake shoes of light and heavy motor vehicles.
We are aware that the trend, if it can be so described, n the direction of metal lining emanates from the 'U.S.A.The quality of much of the home-produced mile lining may be held accountable for the natural lesire to get something better. On this we can remark hat our Ferodo factory in New Jersey Is kept working s.t full pressure producing high-quality fabric lining to eplace metal.
We agree that Mr. Seagrief is entitled to express' his particular views, and we take no exception to his remarks, but submit he is in error in his facts and that us opinion is entirely unsupported by practical evidence.
We wish we could state with equal conviction what the ultimate issue will be, but this is certain—that the system, of brakes in general use to-day is byno means the last word, but neither this consideration nor the prediction of Mr. Seagrief will deter us from pressing on with the extensions of our works, which are necessary to cope with the ever-increasing demand for fabric brake lining.--Yours faithfully, FEnono, LTD., F. J. Field, Chief Engineer, Chapel-en-le-Frith,