For DRIVERS. MECHANICS & FOREMEN.
Page 31
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 publish on this page, and an EXTRA EWA' SHILLH(GS to the sender of the one whi;ch we select as being the best each week. All notes are edited be/are being published. Mention your employer's name, in confidence, as evidence of good faith. Address, D., M. and F., "The "
Commercial Motor " 7-15, .Rosebery Avenue, London, E.C. 3.
Lamps Alight.
.0n. Saturday, January .29th, light your lamps at 5.11 in London, 5.5 in Edinburgh, 5.3 in Newcastle, 5.15 in Liverpool, 5.15 in Birmingham; 5.21 in Bristol, and 5.58 in Dublin.
Replies to "Worried Driver."
We published last week the first of the. letters received in reply to a letter signed "Worried Driver " [December 21st issue, letter No. 2,169] which dealt with an oiling difficulty' on a two-cylinder Thornycroft engine, and we include herewith a further selection from the many letters which have come to hand. Many of these are extremely short, and although we shall publish some of them in our next issue, we shall depart from our usual awards and pay 7s. 6d. to the writer of each letter.
The sender of the following communication has been awarded the extra, payment of 5s. this 'week.
{21-.81] " A.E.K:" (Derby) writes :—" I should like to offer a few.suggestions to 'Worried Driver,' who wrote recently concerning some trouble that he
IA as having with one of the big-ends of a two-cylin der engine. .
"Whenever forced feed lubrication is employed and persistent big-end trouble is encountered, the fault can generally be traced to some defect in the main bearings.
" One case which I had was similar to that mentioned by your correspondent in that it was always the big-end nearest to the flywheel that gave trouble. I never discovered a complete cure in this case, but managed to keep running by almost daily adjustment of the main bearing next to the flywheel.
"Another case of big-end trouble was eventually traced to faulty fitting of the main bearings, the joints of one of them not being brought butt and butt —this is a thing which may very easily happen, particularly after the bearings have been re-metalled, especially if they are re-bored justa shade, on the small side. What. then happens is that, when the bearings are being scraped and bedded-in the. fitter keeps his attention fixed on the body of the bearing,
and is intent on getting a good contact, without noticing whether there is any gap between the two joints. The effect of this particular error is ilhistrate.ci. in Fig. 1 of the accompanying sketch.
"Sometimes, however, trouble of another kind is caused when the bearing-is worn and has become a little -Leo large for the journal. Adjustment is usually effected by filing up the joints between the two halves, and subsequently bedding the bearings in place. 'Unless the filing of the faces of. the joint is very correctly-done, the faces may be filed somewhat round with mi.:effect illustrate.d. in Fig. 2. "in either of the above two eases the result, so far as oiling is concerned, would be that the big-end would be lubricated whilst -the oil was cold and fairly stiff. After a, few miles of running, however, when the engine and the oil had got warm and the latter much thinner, the lubricant would escape through the imperfect joints of the main bearings, thus starving the. big-end. " The same result, will occur if the bearing is fitted to the crankshaft journal, as shown in Fig. a. "Another point to watch when fitting main bearings is the length of the oil grooves. Care should be taken that these do not approach too closely to the outside edge of the bearing, as, if they do, there is a tendency for the oil to run out tinder pressure. "When a. 'big-end or a main bearing has been fitted or adjusted it ie possible, with. a little ingenuity, to test the oil circulation system. before finally erecting the engine. Leave off the bottom half of the bearing, procuring an ordinary hand pump and some light grade oil, and ;pimp this in through some accessible union in the piping system. Arrange for someone to watch the oiling. indicator whilst you manipulate the hand pump until the pressure approaches that Usual when the engine is working Meantime, watch. for the appearance of oil, either at the ends of the main bearing or running from beneath the half of the big-end which 'is in place. If very little leaks from the main bearing and the bigend appears to, be copiously lubricated, you may then rest pretty well assured of the pos.sibilitie.s of the bearings standing up to their work on the roads."
{21821 " E.T.D." (Newcastle-on-Tyne), writes If new main bearings have been fitted itis quite possible that the mechanics have cut some unnecessary oil grooves in the rear end hearing which are allowing the oil to flow away. from the crankshaft bearing instead of feeding the big-end. They should be examined with a view to discovering whether this is the case. Possibly the connecting rod is not iri proper alignment and should be tested for this after being properly fitted and set up on its journal. "The crankpin may have Worn slightly oval so that, when the piston is on either dead centre, the. fit. between .bearing and journal is a little tighter than it is at, an interinediate. point. It. is quite. possible in these circumstances for the journal to overheat to such an extent as to cause the white metal to run.
"'Some mechanics have a habit, when erecting a connecting rod bearing, of turning it out from the shop a Shade on the tight side, the idea being that it will then bed itself in: The result is that the metal, thus ground off the bearing, gets into the oil hole, and stops the flow of lubricant.
"If, on examination, none of these fault § can be discovered, the water circulation should he examined by 'Worried Driver,' particularly in regard to the rear cylinder, so as to make sure that that part of the engine is not overheating."