ROADSIDE AND GARAGE.
Page 73
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Interesting Contributions from Our Driver and Mechanic Readers.
Obstinate Gudgeon Pins and Valve Springs.
wE have at times described various ingenious methods of dealing with obstinate gudgeon pins when removing them; most of these tips, however, related to methods of holding the piston while force was applied to the end of the pin. A correspondent, "T.M.," of Brighton, strikes a new note when he calls attention to the risk that is often run of cracking a piston when the pin is tight in the hole near to the screw that is being used to force the pin out. In such a case the piston has to bear the whole of the compression, the play which usually exists between the smallend boss and the bosses of the piston being such that the connecting rod boss cannot be relied upon to take any compression.
The method used by " T.M." is to measure the play and to make a forked piece which -will fit between the bosses as shown. Armed with this and one of the contrivances recently described, where two chains embrace the piston while a screw acts upon the end of the pin, no harm can be done to the most delicate piston.
When replacing very stiff valve springs, "T.M." has found that in seine engines, especially the Morris, owing to the valve chest being somewhat small, there is difficulty in getting the springs in place. To overcome this he makes a loop of flexible wire—Bowden inner cable will do—and fixes both ends to a piece of wood about 8 ins, long; he then passes the loop through the valve guide and the washer and spring, then he puts a short piece of -P-6-in. rod through the loop and, with the wood as a lever, he draws the wire into its place, and by removing the rod all is ready for the Insertion of the valves.
Fitting Exhaust Pipes to Engines.
ONE of our correspondents, "II.J.G.,"
of Highgate, who is engaged on the repair of all sorts of commercial vehicle and has also had long experience in the shops of manufacturing firms, calls latention to the difficulty of ensuring a gas-tight joint between the exhaust Pipe and the flange on the engine pipe.
It is not an uncommon thing to see a flange broken through being bolted up against the flange of a pipe that was not bent to exactly the right angle to allow the two flanges to meet properly.
Our informant tells us how he haa seen time wasted by men carrying pipes backwards and forwards to the forge to have them bent to the exact angle. He contrasts this waste of time with what he has seen in a factory where the flanges of exhaust pipes were made as shown in his sketch on the left, where a spherical projection is provided to engage with a recess in the flange of the engine pipe. With this arrangement no gasket is used, the projection being turned with a gauge tool and the recess being bored with the cutter shown, producing a gas-tight joint which is to a large extent self-aligning, as shown in an exaggerated form in his sketch.
Our correspondent tells us how he has altered existing pipes which require accurate alignment, to self-aligning joints as shown in the right-hand view. The rose cutter is inserted in both flanges to form a seating for the spherical nipple.
In bus and coach work it is very annoying to passengers to hear the noise of a leaky exhaust when a gasket blows out, as they do sometimes. The plan' be recommends appears to offer such advantages over the usual method that we are surprised that it should not have been more generally adopted, especially when it is taken into consideration that it has given satisfaction on one make for so many years.
Fitting Cardan Shafts and Couplings.
A CORRESPONDENT, "E.W.Y.," of Cardiff, writes as follows :—" There are some points worthy of consideration when fitting up cardan shafts and couplings. The life of a flexible disc depends to a great extent on the align
ment of the shaft, for the slightest whirling will throw an unequal strain on the fabric and very quickly increase the running out of truth, rapidly ending in the rupture of the disc.
"The sliding end of the cardan shaft, which allows for the difference in length due to the rear-spring movement, should be fitted so that it can work freely and be provided with ample means for lubrication, as it will be seen that should this plunger joint become seized the discs will be called upon to take a thrust.
"The forks or spiders on the shaft should be fitted so that they do not distort the discs when the bolts are tightened. It is always advisable te try the bolts in the discs and spider holes before erecting and to ensure that they are a nice tapping fit. Great care must be taken when tightening up the nuts not to squeeze in the fabric, as in doing so it would set up unequal stresses and quickly deteriorate the material around the bolt holes."
The Easy Starting of a Stiff Engine.
SO many suggestions have been given us on the subject of the difficult starting of large engines that we should have thought that our correspondents must have run the whole gamut of possible remedies. A writer, "J.R.G.," of Battersea, however, raises a new point when he suggests that instead of allowing the mixture to be drawn into the cylinders he gets some one else to turn the crankshaft while he blows down a rubber pipe held over the needle boss of the carburetter.
A sharp pull up whilst blowing, he tells us, appears to have the desired effect. He attributes the fact to the warm breath having an effect in vaporizing the petrol, but we can hardly follow this, as all that would take place would be to put a pressure on the petrol in the float chamber, which would make the petrol rise from the jet in the form of a spray.
Our correspondent says that all other parts should be in order.