Engineering reminiscences contributed to "Power" and "American machinist"

by Charles T. Porter

The solid end connecting-rod appears in this engine. This was shown to me by Mr. James Gulland, a Scotch draftsman at Ormerod, Grierson & Co.’s. He did not claim to have originated it, but only told me that it was designed in Scotland. I saw at once its peculiar value for high-speed engines. Every locomotive designer knows the pains that must be taken to prevent the straps on the crank-pins from spreading at high speeds, under the pressure exerted by the transverse fling of the connecting-rod. This solid end renders the connecting-rod safe in this respect, even at thousands of revolutions per minute. For single-crank engines, on which only it can be applied, it is invaluable. This solid rod-end possesses also another advantage. The wear of the crank-pin boxes and that of the cross-head-pin boxes are both taken up in the same direction, so the position of the piston in the cylinder will be varied only by the difference, if any, between the two. With a strap on both ends, the connecting-rod is always shortened by the sum of the wear in the two boxes. The solid rod-end enabled me to reduce the clearance in the cylinder to one eighth of an inch with entire safety. The piston never touched the head.

As this construction was shown to me, the wedge was tapered on both sides. It seemed that this would be difficult to fit up truly, and it also involved the necessity of elongating the bolt-holes in the rod, so that the wedge might slide along in taking up the wear. I changed it by putting all the taper of the wedge on the side next to the brass, making the other side parallel with the bolt-holes. This enabled the opening in the rod-end to be slotted out in a rectangular form, and made it easy for the wedge-block to be truly fitted.

While on this subject I may as well dispose of the connecting-rod, although the other changes were made subsequently, and I do not recollect exactly when. The [following] shows the rod and strap as they have been made for a long time. The taper of the rod, giving to it a great strength at the crank-pin neck to resist the transverse fling, was, I presume, copied by me from a locomotive rod. The rounded end of the strap originated in this way. I had often heard of the tendency of the cross-head-pin straps to spread. This was in the old days, when these pins were not hardened, indeed were always part of the iron casting. The brasses, always used without babbitt lining, would wear these pins on the opposite acting sides only. Brass, I learned afterwards, will wear away any pin, even hardened steel, and not be worn itself. When this wear would be taken up, the brasses would bind at the ends of their vibration, coming in contact there with the unworn sides of the pin. To relieve this binding it was common for engineers to file these sides away. All I knew at that time was that the straps would yield and spread. It occurred to me to observe this deflection in a spring brass wire bent to the form of a strap. The pressure being applied on the line of the pin center, the deflection appeared to take place mostly at the back, and so I stiffened it. Since the introduction of the flats on the pin, which prevent the exertion of any force to spread the strap, this form seems to be rather ornamental than useful.

Connecting-rod and Strap.

To this strap I added a wiper for lubricating the cross-head pin automatically. The drop of oil hung from the center of a convex surface provided above the wiper. The latter was inclined forward, and its edge partook of the vibration of the connecting-rod. On the backward stroke this edge cleared the drop. At the commencement of the forward stroke it rose to take it off.

A note of the change then made by me in stop-valves will conclude the record of these changes. The valve and its seat had always been made of brass. The latter was fitted in a cast-iron chamber, and, expanding more than the iron, was apt to work loose. I disused brass entirely, employing a cast-iron valve in the cast-iron seat. These always remained perfectly tight, showing the additional cost and trouble of brass to be unnecessary.

At the meeting of the British Association for the Advancement of Science in 1863, held in Newcastle, I read before the Mechanical Section a paper on the Richards indicator, illustrated by one of the instruments and diagrams taken by it from locomotives. The paper was very favorably received. The description of the action of the arms, in preventing by their elasticity in combination with a stop any more than a light pressure being applied to the paper, called out especial applause. The president of the Mechanical Section that year was Professor Willis, of Cambridge, the designer of the odontograph form of tooth, which enables gear-wheels of the same pitch to run together equally well, whatever may be the difference in their diameters. I felt very deeply impressed at standing before a large assembly of the leading mechanical engineers of Great Britain, and where so many important things had first been presented to the world, where Sir William Armstrong had described his accumulator, by which enormous power is supplied occasionally from small pumps running continuously, and where Joule had explained his practical demonstration of the mechanical equivalent of heat.

On my journeys to Newcastle and back to London I met two strangers, each of whom gave me something to think about. It happened that each time we were the only occupants of the compartment. Englishmen, I observed, were always ready to converse with Americans. Soon after leaving London, my fellow-passenger, a young gentleman, said to me, “Did you observe that young fellow and young woman who bade me good-by at the carriage door? He is my brother, and they are engaged. He is first mate on a ship, and sails to-morrow for Calcutta. He hopes on his next voyage to have command of a ship himself, and then they expect to be married.” I did not learn who he was, but he said they were making large preparations to welcome the scientists, and added that he owned about six hundred houses in Newcastle. Evidently he was the eldest son.

On my return my companion was an elderly gentleman, a typical Tory. He waxed eloquent on the inhumanity of educating the laboring classes, saying that its only effect must be to make them discontented with the position which they must always occupy.