For DRIVERS, MECHANICS, & FOREMEN.
Page 35
If you've noticed an error in this article please click here to report it so we can fix it.
TEN SHILLINGS is paid to the sender of any letter which we vublish on this page, and an EXTRA FIVE SHILLINGS to the sender of the ins which we select as being the best each week. At notes are edited before being published. Mention your employer's name, in conAdence, as evidence of good faith, Address, D., M. and F., "The Commercial Motor," 7-15, Rosebery Avenue, London, B.C. I.
Lamps Alight.
On Saturday, February 5th, light your lamps at 5.24 in London, 5.16 in Edinburgh, 5.14 in Newcastle, 5.26 in Liverpool, 5.26 in Birmingham, 5.32 in Bristol, and 6.9 in Dublin Re.pries to "Worried Driver." •
The following short letters are taken from many we have received offering suggestions and advice to "Worried Driveir," whose letter, dealing with an oiling difficulty on a two-cylinder Thornycroft engine, appeared in our issue for December 21st. As stated last week, we are departing from our usual awards on this occasion, paying the gender of each letter 7s. 6d. ; we shall revert, however, to our usual rates, as enumerated at the top of this page, as soon as the remainder of these letters has been published.
[2183] " S.W." (York) writes :—" I had just the same trouble myself as W Or rie d Driver' about 12 months ago—a bearing running out every 100 miles or so, and usually the same one gave trouble on each occasion. Once, however' I happened to remove the bottom half of the main bearing for examination, and found the oil hole of the shaft to be half blocked up with white metal. The consequence was that, although the main bearing got plenty of oil and was well lubricated, little, if any, ran through to the bigend. I cleaned this hole and slightly counter-sunk, and have not had any trouble for the last six months."
[The trouble referred to is shown diagrammatically in No. 3 of our group of illustrations.] [2184] " II.G." (Southampton) writes :—" Some time ago we had a lorry repaired as an emergency at a wayside garage. Amongst other things, new main bearing brasses were supplied and fitted. Qn, completion, the lorry was driven home, a. matter of 50 mites, and a short journey next day—perhaps another 50—total 100 in all. A big-end went, and subsequent examination disclosed the Cause. It should be noted that, while Worried Driver's' sketch was substantially correct, he omitted to point out that the oil hole in the main bearing is not in the centre of its length, but is slightly to one side [ea shown diagrammatically in sketch No. 1]. Ei.idently, in the case of our wagon, when erecting the engine after repair, the fitter had overlooked this point, and had put the brasses in the wrong way round, so that the holes in the brass and in the body of the bearing were not in line. The consequence was that neither a • big-end bearing nor main bearing received any oil. T h e • connecting rod, however, being more highly stressed, gave out first.
"Another point to which he might direct his attention at the same time is in connection with the packlags or shims between the halves of the big-end bearing. These arc about 3-16th of an inch thick, being cut away in the centre in the usual way, thus forming oil pockets which receive their supply from the drilled crankshaft, as the hole in the journal comes opposite to them. Now, if the ends of these shims do not fit closely to the crank-pin, the oil has the opportunity to escape there quickly [as shoan in diagram No. 41 instead of distributing itself over the whale bearing surface. It is subsequently thrown off by the centrifugal effect of the quickly revolving crankshaft," [2185] ",G.W.G." (King's Lynn) writes :—" I suggest that 'Worried Driver ' examines the oil grooves in the main bearings to make sure that they are not cut too near the end of the brasses [as shown in diagram No. 21 thus allowing the oil to escape. If they are itwill be necessary to re-metal the brasses and re-cut the grooves to within half an inch of the end of the bearing."
[2186] " L.E.R." (Liverpool) writes :— "'Worried Driver' should remove tee bottom half of his crankcase, take out the caps of the big-end bearings and fit them wait oil scoops. He should ascertain a suitable level of oil into which these se.00ps would just dip and, having done so, he should drill a hole in the crankcase at that level and fit it with a small tap., The crankcase must then be filled with oil to the level of the tap each morning."
[2187] " Experienced " (Leeds) writes :—" I have had a fair amount of experience with twin-cylinder Thorny-croft engines and am of the opinion that, if Worried Driver's oil pump is in good order, one or other of the following will be found to be the source of his misfortunes. (1) The main bearing at the flywheel end of the crankshaft is cracked [as shown in 'diagram No. 3]. (2) The main bearings are worn to such an extent that they are allowing the oil to rim out at the ends. (3) The big-ands are being badly fitted.. His trouble will continue-until the engine is taken down completely, main and bigends properly fitted, crankshaft ovorhauled, straightened if necessary, and reground' if required. Finally, all oil holes must be thoroughly cleaned out with paraffin or petrol.," [Further letters on this subject will be published • next week.—Enn5.?3