US2289941A - Method of expanding pistons - Google Patents

Description

y 14, 1942- H. K. SWITZER METHOD OF EXPANDING PISTONS Original Filed Aug. 3, 1940 2 Sheets-Sheet l INVENTOR.

a/m lw y 4, 1942 H. K. SWITZER 2,289,941

METHOD OF EXPANDING PISTONS Original Filed Aug. 3, 1940 2 Sheets-Sheet 2 g l W INVENTOR. BY WKWL. 4/775 Aim ATTORNEYJ i atented 'July 14, 1942 UNITED STATES PATENT OFFICE 2,zs9,941 I METHOD OF EXPANDING rrs'rons Hamid K Switzer, Newport, Ky.

Original application August a, 1940, Serial No.

350,426. Divided and this application April 17, 1941, Serial No. 389,045 Claims. (01. so-5) This invention relates to the art of expanding -.or reshaping pistons which do not fit tightl in the cylinder. Specifically, it relates to a method of expanding the circumference of a worn piston to completely restore or closely approximate the original contour.

In the operation of internal combustion en-' gines, all types of pistons invariably become collapsed or misshapen after a time due to the repeated expansion and contraction to which they are subjected under varying temperature conditions. The lack of a tight fit between the piston and the cylinder resulting from the collaps or distortion of the piston is objectionable, primarily, because it materially decreases the efliciency of the engine and has a marked eiIect on the economy of operation. The objectionable piston "slap commonly heard in older engines is a characteristic symptom of the defect.

Methods of expanding pistons heretofore practiced have been open to a number of objections.

First of all, there has been no method which could be used effectively with each of the many types of pistons now in common use. In addition, the only really effectiv methods have required cumbersome and expensive machinery and equipment. In all prior known methods. it

has been necessary to dismantle the engine and remove the pistons before they could be properly expanded.

In contrast, one object of the present invention has been to provide a very simple method by which pistons can be reshaped and expanded while they are still inthe engine. The same method can also be practiced after removal of the pistons but with a material saving in time and effort over prior methods. The method of the present invention is adapted to be practiced effectively on each of the various types of pistons now in commercial use.

In substance, the present invention contemplates a method in which the piston skirt is subjected to pressure, preferably rolling pressure, along a plurality of lines extending longitudinally of the skirt. This pressure is applied both on the inside and outside of the skirt and must be sutliciently strong actually to deform or displace slightly the metal of the skirt. Pressure applied in this manner squeezes the displaced metal circumferentially away from the lin of contact, The result is an over all increase in thd external circumference of the piston sufllcient to provide a tight flt between the piston and the cylinder wall.

In accordance with the practice of the method,

ation of these two wheels.

the pressure applied along any single line is relatively slight so that it is very easy to gauge the amount of expansion required in anyparticular piston. The type of pressure applied in the preferred practice of the invention is a rolling pressure in which a rolling element such as a wheel having a rounded or tapered periphery is placed against the interior of the piston wall. Simultaneously, a second wheel may contact the outer surface of the piston wall along a line directly opposite, through'the piston wall, the line contact d by th first wheel. A pressing or squeezing operation is performed by the cooper- The outer wheel tends to flatten the metal forced outwardly by the inner wheel and thereby provides a more uniform expansion of the metal.

For use in the practice of the method, the invention contemplates a simple and inexpensive tool which is the subject matter of my co-pending application S, N. 350,426, filed August 3, 1940. All claims to this tool per se have been included in this co-pending application. However, in order to illustrate the practice of the method, I have illustrated herein a tool similar to that illustrated in my co-pending application as a representative'instrumentality useful in the practice of the method of this invention.

This tool includes a pair of hardened metal wheels. one of whch may have a fiat periphery of substantial width. The other wheel may have a periphery which relatively thin and'either rounded or slightly tapered. These two wheels may be arranged to cooperate with one another to exert a pressing or swaging action to thin the metal of a piston skirt placed between them.

As the tool is normally used, the narrow wheel may roll on the interior of the piston skirt and the broad wheel on the exterior. A handle may be attached to parallel metal bars on which the wheels are journalled. Means may be provid:d for directing these bars to and from on another in order to provide greater or less clearance between the wheels thereby to adjust the pressure which the wheels exert upon the metal.

One of the important advantages of the method involving the use of this tool is that it is possible to expand pistons without dismantling th pistons from the engine block. For instance, with the oil pan and the connecting rods and bearings removed, the piston which is to be operated upon is drawn downwardly to a point at which the piston skirt is disposed beneath the block. The skirtis thenaccessible and may be readily reshaped and expanded.

Another important virtue of the method is that it is applicable to substantially all types of pistons: those made of cast iron and semi-steel Figure 1 is a perspectiveview showing the practice of the process by a simple hand tool of the type hereinbefore described.

ened, while the other, 23, has a periphery which is wide slid flat.

Figure 2 is a fragmentary sectional view taken longitudinally through the piston.

Figure 3 is a sectional view taken on line 3-3 in Figure 2.

Figure 4 isa side view of the tool shown in Figure 1 with the details of .construction shown in section.

Figure 5 is a view similar to Figure 2 showing the practice of th method by a slightly modifled tool on a piston having a strengthening ridge near the lower edge of the skirt.

Figure 6 illustrates a modified form of the tool in which a stationary swage block has been substituted for the wheel having th thinner Deriphery.

, Figure 7 is a sectional view taken on line 88, Figure 6, further illustrating thi particular modification.

Figure 8 is a diagrammatic sectional view taken laterally-through one of the cylinders of an internal combustion engine illustrating the method or expanding a piston without removing it from the cylinder.

Figure 9 is a perspective view showing 'a method of using the tool to expand a piston that has been removed from the engine;

Figures 10- inclusive represent side elevations of various types of pistons in which the practice of the invention has been diagrammatically illustrated, the lines I in each figure representing pressure lines. These various types of pistons are as follows: Figure 10, T-slot skirt;

Figure 11, split skirt; Figure 12, U-shaped slot;

Figure 13, solid skirt; Figure 14, slipper piston; Figure 15, lower ring skirt.

In the drawings, Figures 1-9 inclusive, the piston illustrated is a more or less conventional aluminum alloy piston having a T-slot skirt. The application of the present method to the other common types of pistons will be discussed, however, at a later point in this specification. The thin walled portion of the piston, termed the skirt, has been indicated throughout as IS.

The tool illustrated in the drawings combines two arms [6 and II. The arms are secured to a bracket I 8 by nuts which engage threaded end portions I 9 extending, through holes in the bracket. from the ends of the arms. The arms extend substantially parallel to one another from the bracket. The bracket is bent downwardly at an angle to the arms as at and is secured to-a handle 2| by a bolt or other means. A pair of wheels 22 and 23 is mounted in slots in the.

ends of the arms respectively. These wheels may be journalled on pins 24 press fitted in appropriate holes in the respective ends of the brackets. One of the wheels 22 has a periphery which is narrow and rounded or sl shtly sharppiston from the cylinder.

the position of the arms.

one another. The adjustmentmeans disclosed comprises a screw 25 which is threaded into one of the arms and looked therein by a nut 28.- This screw extends at right angles to the arm and passes through a hole in the other arm. Beyond the second arm the screw is engaged by a wing nut 21. Thus, by tightening the wing nut the two arms will be drawn together. A slight sprinsiness in the arms is of material assistance in producing evenness in the operation of the col.

The expanding operation may be performed as has been the practice heretofore by removing the When this is done the piston may be clamped in a vice 28 (see Figure 9) with the connecting rod 28 still attached. When an aluminum alloy type of piston is being expanded the wheels of the tool are first rolled up and down the skirt on both sides of the slot as near the pin bosses as is practical. The wheels should be rolled longitudinally of the piston in substantially straight lines, with the thinner or rounded wheel on the inside of the skirt. After each stroke, the tool may be moved nearer the slot. In pistons of this type it is only necessary to roll an area of approximately of an inch from each pin boss. Five or six strokes of the tool at each point are usually suillcient to expand the piston about four to six one-thousandths of an inch. In aluminum alloy pistons,

. the tool should be adjusted so that the wheels exert only a light squeezing pressure on the metal of the piston skirt since it is not necessary or desirable to gouge the metal.

The same procedure may be used on semi-steel pistons, that is, the skirt may be rolled or squeezed near the pin bosses on the side opposite to the one on which the thrust occurs.

In the various types of pistons illustrated in Figures 10-15 inclusive the point or points of application of the pressure lines are illustrated diagrammatically. In the slotted pistons, such as Figures 10, 11 and 12, the rolling or squee operation is performed as near the pin bosses as practical, and in the case of the T-slot skirt and split skirt shown in Figures 10 and 11, between the slot and the pin bosses. In the U-shaped slot shown in Figure 12, it is impractical to roll between the pin bosses and the outer arms of the slot so that the operation is performed between the extremities of the arms of the slot and the edge of the skirt. In the slot type pistons the practice of the method of the invention ever, the bulging is outwardly so that the result in all cases is to spread the slot to apoint where it approximates its original shape even though in many cases the slot has become completely closed by the collapse of the piston.

In the lower ring skirt type of pistons the result of the practice of the method is substantialiy the same, although the operation is slightly different due to the fact that the rolling operation must be performed on both sides of the groove. In the use of the tool illustrated, this can readily be accomplished by adjustment of Only a very light pressure is required below the groove, 32.

In the solid skirt type of pistons illustrated in Figures 13 and 14, the pressure 'is applied over the skirt in the area directly oppodte the center of the thrust. As distinguished from the effect of the method on slotted aluminum pistons, the same operation performed on solid skirt cast iron pistons causes the metal to bulge out at the exact points where the pressure is apphed.

In Figures 6 and 7 a modified form of the tool is shown. In this modification a stationary block has been substituted for the inner wheel. This block may be secured in a slot in the end of one of the arms by a pin 30. The operating surface of the block comprises a rounded ridge 3| similar to the rounded peripheral ridge of, the wheel.

One of the principal advantages of the present method is that in many instances pistons may be expanded without completely removin them from the cylinders. The manner in which this is accomplished is disclosed in Figure 8. This method is not applicable to V-type or radial engines. To prepare the piston, the oil pan and the connecting rod bearings'are removed. The

piston to be expanded is then pulled down to expose the skirt, and the connecting rod 29 and crankshaft 32 are moved to one side as shown in Figure 9. In most engines the piston can be brought down to rest on the throws of the crankshaft. The method of expanding the piston can then be practiced as previously described. The piston may be slipped back in place to check the fit as the expanding operation proceeds.

From the foregoing description the method of displace the metal of the piston along a plurality oi continuous lines longitudinally of the piston skirt.

2. The method of expanding pistons which comprises the application or pressure sufiicient to displace the metal of the piston along a series of narrow continuous lines longitudinally of the piston skirt and on the interior surface thereof.

3. The method of expanding collapsed pistons which comprises squeezing the wall of the piston skirt with suflicient pressure to displace the metal along a series of narrow unbroken lines longitudinally of the skirt and disposed generally on the side of the skirt opposite the thrust.

4. The method of restoring the shape of slotted pistons which comprises squeezing the skirt portion of the pistons with suflicient pressure to u displace the metal along a series of unbroken longitudinal lines between the pin bosses and the slot.

5. The method of expandingcircumferentially a collapsed piston which method comprises the application of a rolling pressure suflicient to displace the metal along a series of narrow lines on the interior of the piston skirt, said lines being generally longitudinally disposed.

6.'A method of reshaping a piston comprising compressing the skirt portion in the areas adjacent the pin bosses on the side of the piston opposite the thrust, between two wheels as they are rolled longitudinally of the piston, the outside wheel having a substantially wide flat tread and the inside wheel having a narrow rounded tread.

7. A method of reshaping a cast iron piston comprising compressing the skirt portion in the area opposite the thrust side of the piston between two wheels as they are rolled longitudinally of the piston, the outside wheel having a substantially wide flat tread and the inside wheel having a narrow rounded tread.

8. A method for reshaping a piston skirt which comprises swaging the metal of the piston skirt by contacting the metal of the skirt under pressure along a plurality of continuous adjacent lines extending in a direction longitudinally oi the piston.

9. The method of expanding a piston which comprises the application of pressure progressively along the wall of thepiston skirt in substantial parallelism with the axis of the piston; said pressure being suihcient to displace the metal of the piston skirt circumferentially.

10. The method of expanding a worn piston which comprises the application of pressure suflicient to displace the metal 0! the piston lineally along the piston skirt and longitudinally of the axis of the piston.

HAROLD K. SWITZER.

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